Fast Food Online Delivery Purchase Behaviour in the Presence and Absence of Price-based Incentives
Phase: NA
Conditions: Food Purchases, Eating Behaviour
Sponsor: University of Liverpool

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Title: Fast food online delivery purchase behaviour 
in the presence and absence of price-based 
incentives.  
 
 
Date: 19/01/2026 
 
 
 
 
 
 
 
 
 
 
 

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Description: A study examining differences in food purchasing behaviour when price-
based incentives are present (control) vs removed.  
Contributors: Amy Finlay, Rebecca Evans, Andrew Jones, Martin O’Flaherty, Zoé 
Colombet, Nick Townsend, Zoi Toumpakari & Eric Robinson 
Category: Project 
Affiliated institutions: University of Liverpool, Liverpool John Moores University, 
University of Bristol 
License: CC-By Attribution 4.0 International 
Subjects: Psychology, Life Sciences, Health Psychology, Nutrition, Obesity Policy 
Background 
Consumption of out-of-home (OOH) food is associated with significantly greater energy 
and less-healthy nutrient (i.e. fats, salt and sugar) intake(1). Specifically, OOH eating 
occasions contain 197 additional kcal compared to non-OOH eating occasions. This 
increase appears to persist into daily energy intake with only minor compensation(1). 
Consumption of OOH food therefore contributes to obesity and associated ill-health.  
The price of food is a key consideration of food choice, particularly for individuals of 
lower socioeconomic position (SEP)(2). It is estimated that 23% of money spent on food 
is consumed OOH for UK adults(3), where financial incentives appear to be more widely 
available for less-healthy foods than healthier foods (4, 5), and have been shown to 
increase the likelihood of purchase of promoted items(5). Research by Public Health 
England estimated that approximately one-third of foods purchased in supermarkets 
were on price promotion in 2018(6). Equally, recent evidence suggests that 66% of 
outlets on food delivery platforms in the UK offer at least one type of price promotion(7), 
with more promotions offered in outlets in more deprived areas. Due to the existing 
evidence of negative impacts of price-based incentives on dietary quality, the 
government in England have implemented restrictions on volume-based promotions 
(i.e. buy one get one free) in supermarket settings(8). No such restrictions have yet been 
considered for the OOH food sector.   
There are a range of different types of price-based incentive in OOH settings. Three 
common incentives include value pricing, price reductions and bulk-buy reductions(9). 
Value pricing can be applied to items available in multiple sizes, whereby the increase 
in price is disproportionate to the increase in size (i.e. size up for £1 and receive an extra 
50%)(10, 11). Price reductions often refer to a percentage discount, and are frequently 
applied to full menus on food delivery platforms(7). Bulk-buy reductions relate to meal 
deal or bundle options whereby a group of items are provided together at a discounted 
price(12).  

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Little research to date has examined the causal effect of removing price-based 
incentives on purchasing behaviour in OOH food settings. One online randomised 
controlled trial explored the effect of removing three types of price-based incentives 
individually and in combination, on food choice through a virtual food delivery 
platform(9). This study found that energy selection was 7-8% lower when price 
incentives were removed. While not statistically significant, Bayes factors indicted that 
data comparing control vs “all promotions removed” conditions were inconclusive 
(BF10 = 0.55) and therefore could not provide support for the alternative or null 
hypotheses. A limitation of this study is that the outcome was hypothetical food choice. 
As participants would not pay for or receive their selected meals, the prices of foods 
may have been less salient, thus reducing the potential for impact. Studying real-world 
consumer behaviour (as opposed to hypothetical choice) will better determine the 
potential impact of removing price-based incentives in the OOH food sector.  
Hypotheses 
Removal of price-based incentives will be associated with reduced energy purchased 
by households and consumed by household members.  
Evidence suggests that price-based incentives are used more frequently by lower SEP 
individuals(13), therefore we hypothesise that any effects of removing price-based 
incentives will be greater for individuals from lower SEP groups. 
Design Plan 
Study type Experiment – participants will be randomly assigned to one of two 
conditions. 
Blinding Participants will not know the treatment group to which they have been 
assigned. Researchers will also be blinded. Participants will be told they are taking part 
in a study of food choice and diet-related health beliefs to disguise the true aims of the 
study.   
Is there any additional blinding in this study? N/A 
Study design Participants will be recruited online through social media to complete a 
study of food choice and health beliefs, where they will be required to place a real order 
with a specified outlet for themselves, and other adults in their household.  
The study will be conducted online. Participants will complete a short screening 
questionnaire to ensure they meet the eligibility criteria and provided access to the 
study platform. Participants will be randomised to one of two conditions (control vs 
price incentives removed) and then order a meal for themselves, and on behalf of their 
household, through an online platform resembling a food delivery app for a pizza outlet.  

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Participants will then be transferred to an outlet’s payment and delivery scheduling 
system to schedule their order for the same day or the following day and then return to 
the study platform. Participants will be asked to upload proof of purchase (i.e. a receipt 
from the food outlet) and any reasons for deviation from the original order selected, as 
well as the scheduled date and time of delivery. 
If ordering for a multi-person household, participants will provide the email addresses 
for other adults in the household who will have the option to become participants in the 
study. A follow-up questionnaire will be completed by all adults in the household who 
consent to taking part. The study will be created on the online research platform 
Qualtrics(14). 
Menus 
Local franchise outlets of a large UK chain outlet Tops Pizza was approached  as this 
chain offers common financial incentives used by other chains and identified in 
previous research(9): 
1) Product price reductions (e.g. 20% off orders – available through a voucher code) 
2) Bulk buy reductions (e.g. meal deal for one person/family bundles) 
3) Value pricing (e.g. size up for a small price increase) 
Multiple of the chain’s franchises (outlets) based in England will be used in the present 
study, as it provides a range of postcodes eligible for food delivery. Food menus will be 
presented to participants in the form of a virtual food delivery platform resembling the 
Tops Pizza website.  
For both conditions, all available items on the Tops Pizza menu for the selected 
franchises will be presented. This menu consists of n=29 pizzas (available in small, 
medium, large size), n=24 side dishes, n=7 dips (available in small and large size), n=16 
desserts, n=12 drinks and n=7 meal deal/bundle options.  
Baseline size, price and calorie information are taken from the Tops Pizza website. The 
menu items and prices will be frequently monitored to ensure the virtual platform 
resembles the real website at all times. On all menu pages, a statement at the bottom 
of the screen will read “a 50p service charge will be added to all orders”.  
Price-based incentives 
The control condition will have all price-based incentives present (resembling the 
current chain’s pricing structure and promotions), and the intervention condition will 
have all price-based incentives removed. 
Product price reductions 
In the control menu, at the top of each page a message will describe the price reduction 
available (e.g. “20% off order with code XXX”). All original prices will be shown crossed 

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out, with discounted prices next to them. In the price incentives removed condition, all 
items will be shown with their non-discounted prices, and no discount code will be 
made available. 
Bulk buy price reductions 
N=7 bulk buy (meal deal/bundle) options will be offered for personalisation (listed in 
Table 1). For the food choice task, the menu category will be called ‘set meals’. In the 
control condition, these will be offered at discounted prices. In the price incentive 
removed condition, the same options will be provided, but with no discounted price.  
Table 1: Meal deal & bundle offers available  
Name 
Description 
Personalisation  
The Hungry Man 
Any melt & Garlic Bread or 
Fries  
Choice of n=5 melts, n=2 
side dishes, n=3 drinks at an 
extra price 
Party Pack Deal 
 
Sharing pizza + 2 sides + any 
1.5L drink  
Choice of n=4 sides at a 
regular price, n=9 sides at an 
additional price, n=4 drinks 
The Family Besties 
2 sharing pizzas + 2 sides + 
1.5L drink  
Choice of n=4 sides at a 
regular price, n=9 sides at an 
additional price, n=4 drinks 
The Flying Wiiings 
2 sharing pizzas + 2 sides + 2 
desserts + 1.5L drink  
Choice of n=4 sides at a 
regular price, n=9 sides at an 
additional price, n=4 drinks, 
n=5 desserts 
The Great Double  
3 sharing pizzas + 2 1.5L 
drinks 
Choice of n=4 drinks 
The Home Alone 
 
Vegan individual pizza + 
vegan side + 500ml drink 
Choice of n=3 pizzas, n=2 
sides, n=3 drinks 
 
Volume value pricing 
Pizzas will be available at three portion size options. Existing value pricing (i.e. the price 
increase is disproportionately small compared to the size increase) will be used in the 
control condition. In the price incentives removed condition, proportional pricing will be 
calculated based on the medium size option. This is demonstrated in calculations 
below. This will be applied to all pizzas on menus (35% of menu items). 
 
 
 
 
Randomization: Computer-based random assignment of participants to one of the two 
conditions will be applied upon signing up to the study. The order in which the 
Proportional pricing calculation - Margherita:  
Small = £6.99; Medium = £12.99; Large= £13.99 
Medium to Small size change = - 43.5% 
Medium to Large size change = + 49.68% 

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food/beverage items are presented will be the same order shown on food delivery 
platforms at the time of virtual app creation.  
Sampling Plan 
Existing Data: Registration prior to creation of data 
Explanation of existing data: N/A 
Data collection procedures: Data collection will take place through Qualtrics.  
Participants will be recruited online, including through the use of social media 
advertising, targeted by postcode. Other adults in the same household will have the 
opportunity to join the study as a participant and complete the follow-up questionnaire. 
All participants will be reimbursed for their participation (£15 per person). 
Inclusion criteria: 
• Able to order and pay for a takeaway pizza for delivery today or tomorrow 
• Currently reside in select postcode areas 
o Manchester (M13 store): M1, M2, M3, M4, M5, M11, M12, M13, M14, M15, 
M16, M18, M19 
o Liverpool (L3 store): L1, L2, L3, L4, L5, L6, L8, L13, L15 
o Birmingham (B27 store): B9, B10, B11, B12, B13, B25, B26, B27, B28, B33, 
B90, B91, B92 
• Over the age of 18 years 
• Report having used food delivery services in the last year 
Exclusion criteria:  
• Partaking in a fast or other restrictive eating (e.g. for religious or health reasons) 
at time of participation  
• A previous eating disorder diagnosis 
• Currently on appetite-suppressing medication 
• Dietary restrictions/intolerances including:  
o Gluten-free 
o Dairy-free 
o Sugar-free 
 
Stratification  
To ensure that we have a sample that is diverse in SEP and balanced for other key 
demographics, where possible, we will attempt to recruit a sample that has equal 
numbers of males vs. females, at representative levels of household income and age 
group. 

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Quintiles of average disposable household income in the UK in 2023/2024 were 
obtained from the Office for National Statistics(15). Midpoints of quintiles were 
determined and rounded to the nearest £10,000 to define thresholds for 5 groups of 
household income (Table 2).  
Table 2: Calculation of thresholds for income groups representative of UK population 
 
Quintiles of household 
income (from ONS)* 
Ranges based on quintile 
midpoints  
Final income groups for 
data collection 
1st  
£19,799 
< £26,891 
< £30,000 
2nd  
£33,983 
£26,891 - £40,482 
£30,000 – £39,999 
3rd 
£46,981 
£40,482 - £54,853 
£40,000 – £49,999 
4th 
£62,724 
£54,853 – £74,170 
£50,000 – £69,000 
5th 
£85,615 
> £74,170 
> £70,000 
*Total household disposable income (i.e. income post-tax/national insurance) 
Using data from ONS(16), we calculated the age split of UK adults, whereby 
approximately 50% of UK adults are between the ages of 18 and 48, and 50% of adults 
are 49+. Therefore, we will try and recruit an equal proportion of participants across the 
two age groups.   
Procedure 
Participants recruited online, including the use of social media (Appendix A) and taken 
to a short description of the study (Appendix B), asked to read the participant 
information sheet (Appendix C) and provide consent to take part in the study (Appendix 
E). Participants will complete a short screening questionnaire (Appendix G) to ensure 
they are eligible to take part and can order and pay for a takeaway meal the same day 
for themselves, or on behalf of their household.  
Participants will be randomly allocated to one of the following groups:  
• Control menu 
• Price-based incentives removed 
Participants will be asked to select a takeaway meal for themselves, or on behalf of the 
adults in their household that they will then order from the real food outlet website. They 
will be asked to clarify the number of adults that the food order is for (Appendix H).  
In both conditions, participants will be able to view the different menu categories 
without placing an order. When participants have decided what they would like to order 
for themselves, or on behalf of their household they can select an item which will take 
them to a page to make any amendments related to the item. For example, if they select 
a pizza, they will be asked to select a size. Once participants have made any 
specifications, they can add the item to their shopping basket and either continue 
shopping or ‘checkout’. If they select to checkout, they will be taken to a basket page, 
and asked to confirm their order, or start again. 

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Control menu: At the bottom of each menu page, it will describe the price reduction 
available (e.g. “20% off all orders with code XXX”). Meal deal and bundle options will be 
available at discounted prices. All pizzas will be available at value pricing. 
Price incentives removed menu: Participants will not be shown the available discount 
code. Meal deal and bundle options will be presented but not at discounted prices. All 
pizzas will be shown with proportional pricing.  
When orders are confirmed, participants will be asked to follow a link on the page to the 
Tops pizza website to place the same order and schedule delivery for the same day or 
the following day. They will be asked to return to the study page once the order has been 
placed.  
Participants will return to the study, and upload proof of their order (i.e. a screenshot of 
the order confirmation or the receipt). If there are any inconsistencies between the 
order placed on the study platform and the real order, participants will be asked to 
provide reasons for this. Participants will be told they will receive a link via email to 
complete the follow-up questionnaire and to organise study reimbursement in the next 
24 hours.  
Researchers will email all participants (including the additional adults in the household) 
with a link to the follow-up questionnaire after participants receive their food order (as 
noted by the evidence provided by participants). The follow-up questionnaire (Appendix 
I) will collect data including a measure of health beliefs (in line with cover story), 
participant characteristics, consumption of the food ordered, and opinions on price 
incentives. To estimate energy consumption, participants will be asked if they ate 
anything from the following categories: Pizzas, Starters/Side dishes, Desserts, Drinks, 
Dips.  
If a participant has consumed pizza, they will be asked to select the pizza they ate (from 
a dropdown list) and how many slices they ate. They will have the option to select 
multiple pizzas if they sampled more than one. A similar approach will be used for the 
other categories, but participants will be asked to estimate a percentage of the dish 
they consumed rather than a number of slices. 
On completion of the follow-up questionnaire, participants will be asked to confirm 
their email address, and given a choice of reimbursement options:  
• £15 bank transfer from the University of Liverpool  
o Participants will be made aware that payments can take up to 5 weeks to 
appear in bank accounts, due to university procedures.  
• £15 Amazon voucher 
o Typically received within 2 working days 
• £15 JustEat voucher 

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o Typically received within 2 working days 
Attention checks 
Two attention checks will be included: 
o One question in the follow-up questionnaire, will state: “This is an attention 
check. How many times have you visited the planet Mars? Several times / Just 
once / Never”.  
o Correct answer: Never 
 
o In the food choice motives questionnaire (post-food order), an additional item 
states: “This is an attention check. Please select the answer 2 ‘A little 
important’”.  
o Correct answer: 2 ‘A little important’. 
 
Variables 
Manipulated variables: Control vs. intervention condition (see above). 
Measured variables: 
Participant characteristics 
To compare outcomes by individual participant variables, and to aid stratification, 
participants will be asked to report their gender and age and. Self-reported height and 
weight data will also be collected to calculate body mass index (BMI). Ethnicity data will 
also be collected. 
Measures of socioeconomic position 
Three measures of socioeconomic position will be collected:  
• Highest level of education achieved  
• Equivalised household income 
• A subjective measure of socioeconomic position - MacArthur Scale of Subjective 
Social Status (SSS)(17) 
Education level will be recorded, as there is evidence that individuals with a higher level 
of education are more motivated by health when making food decisions(18). Subjective 
social status will be recorded as this measure has been found to have strong 
associations with overweight and obesity(19). Equivalised household income will be 
calculated by gathering participant’s after-tax household income and household 
composition (number of adults and children in the household). This calculation will 
involve dividing the after-tax household income by the sum of the equivalence value of 
all the household members: first adult = 1, additional adult or child aged 14 and over = 

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0.5, child aged 0-13 = 0.3. This method is used by the Office for National Statistics(20) 
and categorises households into ten deciles of SEP.  
Food choice motives 
The Food Choice Questionnaire(21) will be used to assess the factors that may 
influence participants’ food choices. This questionnaire is comprised of nine factors 
(health, mood, convenience, sensory appeal, natural content, price, weight control, 
familiarity & ethical concern).   
We will collect scores for the four food choice motives most relevant to our outcomes of 
interest, specifically price, health, convenience and sensory appeal. 
Aim guessing  
Participants will be asked what they believe the aims of the study to be. Anyone that 
guesses the study aims to be investigating the influence of pricing on food purchases 
will be coded as being aware of study aims. One researcher will code awareness of 
aims and a second researcher will independently verify.  
Outcome variables 
Orders placed through online platform 
o Total energy ordered 
▪ Used to calculate energy ordered per household member 
o Total monetary spend 
▪ Used to calculate monetary spend per household member 
o Total energy consumed per household member  
▪ Estimated using self-reported data 
Additional variables 
In the follow-up questionnaire, participants will be asked to describe how much of the 
takeaway meal they consumed, and if anyone not included in the study ate any of the 
food (e.g. if any children in the house ate some of the meal). They will also be asked 
about their frequency of use of food delivery platforms and whether they thought their 
food choices were typical for them. Participants will complete 3 subscales of the UPPS-
P Impulsivity scale (negative urgency, positive urgency and lack of premeditation). 
These measures will not be used in any formal analyses. Finally, participants will be 
asked how they feel about the removal of price-based incentives, and whether they 
believe this would be a successful approach to improve eating habits in the OOH food 
sector. Within the follow-up questionnaire, there will be a health beliefs measure to 
corroborate the cover story. 
Study Flow 

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RECRUITMENT 
▪ 
Advertisements will be placed online (Appendix A), targeted to 
individuals in set postcodes, which are within range of delivery 
from the Pizza outlets.  
▪ 
Participants will be taken to a landing page which describes the 
study procedure (Appendix B). 
INFORMED 
CONSENT 
(Inquisit) 
▪ 
Participants will read the information sheet (Appendix C) 
▪ 
Participants who wish to proceed will consent to taking part 
(Appendix E). 
▪ 
Participants who believe they meet the inclusion/exclusion 
criteria will follow a link to complete a screening questionnaire 
(Appendix G) which will confirm eligibility and ensure 
participants understand and can comply to the study procedure, 
and that they will order and pay for a meal for that day or the 
following day. If participants do not meet the eligibility criteria, or 
do not wish to continue they will be redirected. 
RANDOMISATION 
(Inquisit) 
▪ 
Participants will be randomized to one of the two experimental 
conditions (computer-based randomisation). 
FOOD CHOICE 
TASK 
(Inquisit) 
▪ 
Control menu 
▪ 
All price-based incentives 
removed 
▪ 
Instructions will be displayed (Appendix H) 
▪ 
Participants will report if they are ordering a meal on behalf of 
other adults and if so, the number of adults.  
▪ 
Participants will be asked to select the food they will order for a 
meal from Tops Pizza for their household.  
▪ 
Once the food choice is confirmed, participants will be asked to 
follow a link to the Tops Pizza website to place the same order.  
FOOD ORDERING 
(Tops Pizza 
website) 
▪ 
Participants will be asked to schedule their food order for the 
same day, or the following day from the Tops Pizza website.  
▪ 
Participants will return to the study and upload evidence of their 
order (a screenshot of the order confirmation or receipt)  
▪ 
If orders deviate from the online food selection, participants will 
be asked to explain the cause.  
 
ADDITIONAL 
RECRUITMENT 
 
Participants will be asked to provide email addresses of other adults in 
the household who would like to take part in the study and confirm that 
the other adults have consented to sharing of email address.   
QUESTIONNAIRES 
(Inquisit) 
▪ 
Follow up questionnaires will be sent to all participants the morning 
following their food order with unique identifier codes to link their 
answers to the food choice task.  
▪ 
Additional participants will be provided with a participant 
information sheet (Appendix E) and consent form (Appendix G). 
▪ 
This questionnaire will collect data on participant characteristics, 
food choice motives, consumption, and thoughts on policy related to 
price incentives (Appendix I). 
▪ 
Aim guessing in an open-ended response format. 
DEBRIEFING 
(Inquisit) 
▪ 
Participants will be debriefed on study aims (Appendix J) 
PAYMENT 
▪ 
Participants will select their preferred method of study payment and 
confirm their email address. All participants will be reimbursed £15 
via bank transfer or gift voucher. 
 

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Analysis Plan 
Analyses will be conducted in R Studio. Results for primary analysis will be considered 
significant at p < 0.05. To account for multiple testing, results for secondary analysis will 
be considered significant at p < 0.0167. Results for exploratory analysis will be 
considered at p < 0.05 due to their exploratory nature.  
Participant characteristics: 
All participants who have completed the follow-up questionnaire in full, and who have 
provided a valid identifier number connecting them to the food ordering task will be 
included in the analysis.  
Participant characteristics overall and by experimental condition will be reported. Data 
will include age, gender, ethnicity, highest educational qualification, equivalised 
household income, subjective social status and BMI. Continuous variables will be 
summarised by means and standard deviations if approximately symmetrical or median 
(IQR) otherwise, categorical variables will be summarised by counts and percentages.  
Primary analysis 
Firstly, we will examine if there is any evidence of clustering of outcomes by household. 
Evidence of clustering will be an ICC value > .05 and a design effect > 2.  
If there is no evidence of clustering:  
We will conduct a one-way ANCOVA to explore differences in self-reported energy 
consumed between the two conditions (control vs price incentives removed). 
Covariates included in the model will be age, gender, SEP (equivalised household 
income and education) and any household composition or ordering variables (e.g., size 
of household order is made by) associated with the primary outcome. If there is 
covariance between the two measures of SEP, only equivalised household income will 
be included in the model. We will explore whether BMI and food choice motives at the 
individual/household level contribute to variance in the outcome variable. If they do, we 
will include these variables as covariates.  
We will also report results with clustering by household as confirmatory analyses (i.e., 
whether size of intervention vs. control effect is similar in size and direction as in non-
clustered analysis, as opposed to null significance testing). 
If there is evidence of clustering by household:  
A linear mixed model will be used to assess the impact of pricing condition (control vs 
price incentives removed) on energy consumed per household member. We will cluster 
analyses by household, by including this as a random effect and the covariates 
described above as fixed effects.  

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Sensitivity analysis 
If there is evidence of clustering, and there are not many participants from single person 
households (e.g. < 10%) then we will omit these participants and re-run the primary 
models as sensitivity analysis.  
We will also re-run the primary models with participants who guess the aim of the study 
removed.  
Secondary analysis 
We will examine whether SEP (equivalised household income, education), moderates 
the effect of study condition on the primary outcome (energy consumed) by including 
interaction terms in the above primary model.  
Energy ordered by households: Because energy ordered data will only be available for 1 
member of each household (i.e. the majority of participants will not have energy ordered 
data, as energy ordered is by household) and sample size calculation is based on total 
number of participants and not total number of households, we will treat energy 
ordered as a secondary outcome and descriptively report the effect of intervention 
condition (% change in energy ordered and effect size). For the subsample of main 
participants who took part in the food choice task and therefore have individual level 
data for energy ordered (i.e. the household member responsible for ordering), we will 
conduct a linear regression model to explore the size of association between study 
condition and total energy ordered per household. We will adjust this model for gender, 
SEP (equivalised household income, education), BMI, food choice motives and any 
household composition or ordering variables. 
Exploratory analysis 
Further to the earlier moderation analysis, we will explore whether additional 
individual/household-level characteristics such as age, gender, BMI and food choice 
motives moderate the relationship between study condition and our primary outcome 
(energy consumption).  
We will also conduct analyses to explore potential mechanisms for any observed 
effects. For example, we will conduct a linear regression model to assess whether 
condition is associated with the number of items selected. We will conduct logistic 
regression models to assess whether condition is associated with the likelihood of 
ordering a food bundle, ordering a large sized pizza, and ordering a small sized pizza. 
The same covariates in the primary analysis will be included.  
Descriptive analyses 

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For descriptive purposes, we will use the energy ordered by households modelling 
approach (see above) to examine difference in money spent (replacement of dependent 
variable from model above) under the two arms of the study. 
One tailed vs. two tailed statistical testing 
We will adopt and power for a one tailed approach for primary analysis, given that there 
is a strong directional hypothesis regarding the effect of removing price incentives (i.e. 
reduces energy consumption) and this approach increases statistical power given the 
available resources. 
Sample size analysis 
We conducted a power analysis for a one-way ANCOVA using the ‘superpower’ package 
in R. Using an ANCOVA with 6 possible covariates (listed above) that explain ~30% of 
variance in the outcome, and an effect size of d = .20, and power of 80% would require 
440 participants (one-tailed).  
 
Assuming a hierarchical structure to the data (individuals nested within households) 
with the average household size = 2 and similar effect size a multilevel model with 
clustering (VPC ~ .10) would have 82% power [95% CI: 73% to 89%] (using the ‘simr’ 
package).  
 
Our aim will be to oversample (max N = 600) in response to uncertainty in both effect 
size estimates and clustering of data (removal of singletons if necessary). This 
oversampling will improve the precision of our estimates.  However, we will also employ 
a stopping rule (described below). 
Stopping rule 
Prior to starting data collection, we do not know with certainty what the rate of 
participant recruitment will be, and effect size estimates have uncertainty. To balance 
the trade-off between costs (e.g., in research time, participant burden) and likelihood of 

15 
 
the study providing convincing evidence, we will conduct interim analyses of our 
primary outcome to assess whether the results are convincing enough to conclude that 
effects on energy consumption are present at interim and if not, if it is justifiable to 
extend data collection to a final endpoint (e.g., N=600 or similar).  
The interim analyses will examine the effect size of the primary outcome and observed 
statistical significance.  Based on simulations by Kowialiewski (2024)(22), we would 
expect some effect size stabilisation of Cohen’s d with > 150 participants. We will also 
calculate Bayes Factors to assess the strength of evidence for the experimental vs null 
hypotheses.  
We will aim to conduct the interim analysis when we have obtained approximately 50% 
of the estimated pre-study sample size (N ~ 300) and aim to choose a stopping point 
based on scheduling of participants and outlet sessions (i.e. end of April 2026). If at this 
point, the data suggests that it is extremely unlikely that the predicted effect would be 
observed up to maximum sample size capacity based on recruitment to date, or if Bayes 
Factors suggest there is strong evidence for the null hypothesis (BF10 < 0.3) then we will 
schedule a study data collection completion date shortly after the interim analysis. 
If the observed effect size suggests that a condition effect will likely be statistically 
detectable at the maximum sample size possible to achieve (based on recruitment to 
date), or Bayes Factors do not provide support for either the null or alternative 
hypothesis (BF10 > 0.3 and < 3) for our primary outcome, we will continue data 
collection to recruit the largest possible sample size with available resources. At interim 
we will determine the maximum sample size possible to achieve given participant 
recruitment rates and specify the end data collection at this point. For final analyses we 
will adjust p values (dividing by 2 for outcomes examined at interim to account for 
multiple analyses) to account for error rate inflation due to the interim analysis 
conducted. 
 
 
 
 
 
 
 
 
 

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References 
1. 
Garbutt J, Townsend N, Johnson L, Jones A, O’Flaherty M, Colombet Z, et al. The 
contribution of the out-of-home food (OOHF) sector to the national diet: a cross-
sectional survey with repeated 24-hour recalls of adults in England (2023-2024). 
medRxiv. 2025:2025.06.30.25330369. 
2. 
Steenhuis IHM, Waterlander WE, de Mul A. Consumer food choices: the role of 
price and pricing strategies. Public Health Nutrition. 2011;14(12):2220-6. 
3. 
Department for Environment Food & Rural Affairs. Family food FYE 2023. UK: 
GOV.UK; 2024. 
4. 
Powell LM, Kumanyika SK, Isgor Z, Rimkus L, Zenk SN, Chaloupka FJ. Price 
promotions for food and beverage products in a nationwide sample of food stores. 
Preventive Medicine. 2016;86:106-13. 
5. 
Bennett R, Zorbas C, Huse O, Peeters A, Cameron AJ, Sacks G, et al. Prevalence 
of healthy and unhealthy food and beverage price promotions and their potential 
influence on shopper purchasing behaviour: A systematic review of the literature. 
Obesity Reviews. 2020;21(1):e12948. 
6. 
Public Health England. An analysis of the role of price promotions on the 
household purchases of food and drinks high in sugar, and purchases of food and drinks 
for out of home consumption. 2020. 
7. 
Huang Y, Weerasinghe N, Adams J, Rippin H, Hetz K, Zhiteneva O, et al. Menu 
item prices and promotions offered on a meal delivery app in the UK and their socio-
economic patterns. Public Health Nutrition. 2025;28(1):e110. 
8. 
Department of Health and Social Care. Restricting promotions of products high 
in fat, sugar or salt by location and by volume price: implementation guidance. 2023. 
9. 
Finlay A, Jones A, O'Flaherty M, Colombet Z, Townsend N, Garbutt J, et al. Out-of-
home food selection behaviour in the presence and absence of price-based incentives 
in a virtual food delivery app: a randomised controlled trial. Appetite. 2025;215:108228. 
10. 
Vermeer WM, Alting E, Steenhuis IHM, Seidell JC. Value for money or making the 
healthy choice: the impact of proportional pricing on consumers’ portion size choices. 
European Journal of Public Health. 2009;20(1):65-9. 
11. 
Finlay A, Boyland E, Jones A, Witkam R, Robinson E. The impact of calorie 
labelling and proportional pricing on out of home food orders: a randomised controlled 
trial study using a virtual food and drink delivery app. International Journal of Behavioral 
Nutrition and Physical Activity. 2023;20(1):112. 
12. 
Sharpe KM, Staelin R. Consumption Effects of Bundling: Consumer Perceptions, 
Firm Actions, and Public Policy Implications. Journal of Public Policy & Marketing. 
2010;29(2):170-88. 
13. 
Davies T, Coyle D, Shahid M, Pettigrew S, Wu JHY, Marklund M. Packaged foods 
purchased on price promotion in Australia. Appetite. 2023;180:106352. 
14. 
Qualtrics. 2025 [Available from: https://www.qualtrics.com/. 
15. 
Office for National Statistics. The effects of taxes and benefits on household 
income, disposable income estimate UK: Office for National Statistics; 2025 [Available 
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https://www.ons.gov.uk/peoplepopulationandcommunity/personalandhouseholdfinan
ces/incomeandwealth/datasets/householddisposableincomeandinequality. 

17 
 
16. 
Office for National Statistics. Estimates of the population for the UK, England, 
Wales, Scotland, and Northern Ireland UK: Office for National Statistics; 2025 [Available 
from: 
https://www.ons.gov.uk/peoplepopulationandcommunity/populationandmigration/pop
ulationestimates/datasets/populationestimatesforukenglandandwalesscotlandandnort
hernireland. 
17. 
Operario D, Adler NE, DR W. Subjective social status: Reliability and predictive 
utility for global health. Psychology & Health. 2004;19(2):237-46. 
18. 
Konttinen H, Sarlio-Lähteenkorva S, Silventoinen K, Männistö S, Haukkala A. 
Socio-economic disparities in the consumption of vegetables, fruit and energy-dense 
foods: the role of motive priorities. Public Health Nutrition. 2013;16(5):873-82. 
19. 
Goodman E, Adler NE, Daniels SR, Morrison JA, Slap GB, Dolan LM. Impact of 
objective and subjective social status on obesity in a biracial cohort of adolescents. 
Obesity Research. 2003;11(8):1018-26. 
20. 
Office for National Statistics. Chapter 3: Equivalised income.  Compendium: 
Family Spending in the UK. UK2015. 
21. 
Steptoe A, Pollard TM, Wardle J. Development of a measure of the motives 
underlying the selection of food: the food choice questionnaire. Appetite. 
1995;25(3):267-84. 
22. 
Kowialiewski B. The power of effect size stabilization. Behavior Research 
Methods. 2024;57(1):7. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

18 
 
Appendix 
Appendix A: Recruitment text for online recruitment 
Researchers at the University of Liverpool are conducting a study exploring health 
beliefs, food choice and purchases through online delivery platforms.  
You will choose a meal for yourself, or on behalf of the adults in your household and 
order and pay for the meal from a real takeaway pizza outlet to eat the same day or the 
following day.  
The day after your food order, you and other adults in your household will be asked to 
complete a short follow-up questionnaire. Any adults who take part in the study by 
completing the follow-up questionnaire will be reimbursed financially for their time.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

19 
 
Appendix B – Landing page  
Thank you for your interest in our study of health beliefs and food delivery!  
If you take part in this study, you will select a takeaway meal for yourself, or on behalf of 
the adults in your household through an online food choice task. You will then order the 
same food items from the Tops pizza website scheduled for today or tomorrow and 
provide evidence of this order.  
Any other adults in your household who eat the food ordered will have the opportunity 
to join the study as participants. All adults who take part in the study and complete the 
follow-up questionnaire will be reimbursed £15 each, via a bank transfer (estimated to 
be 3-5 weeks) or gift voucher (received within 2 working days – Amazon or JustEat).  
 
If you would like to take part, please make sure you meet the criteria below. A detailed 
information sheet and consent form follow on the next pages.  
• Able to order and pay for a takeaway pizza for delivery today or tomorrow 
• Currently reside in select postcode areas 
o Manchester (M13 store): M1, M2, M3, M4, M5, M11, M12, M13, M14, M15, 
M16, M18, M19 
o Liverpool (L3 store): L1, L2, L3, L4, L5, L6, L8, L13, L15 
o Birmingham (L27 store): B9, B10, B11, B12, B13, B25, B26, B27, B28, B33, 
B90, B91, B92 
• Over the age of 18 years 
• Have used food delivery services in the last year 
Exclusion criteria:  
• Partaking in a fast or other restrictive eating (e.g. for religious or health reasons) 
at time of participation  
• A previous eating disorder diagnosis 
• Currently on appetite-supressing medication 
• Dietary restrictions/intolerances including:  
o Gluten-free 
o Dairy-free 
o Sugar-free 
 
 
 
 

20 
 
Appendix C: Participant information sheet for original participant 
 
Health beliefs and food delivery study 
 
You are invited to participate in a research study. Before you decide whether 
to participate, it is important for you to understand why the research is being 
done and what it will involve. Please take time to read the following 
information carefully and feel free to ask us if you would like more 
information or if there is anything that you do not understand. We would like 
to stress that you should only agree to take part if you want to. 
 
What is the purpose of the study? 
The purpose of the study is to understand health beliefs and consumer habits when 
ordering pizza for delivery. 
  
Why have I been chosen to take part? 
We are recruiting volunteers who fulfil the following criteria: 
1. Can schedule and pay for pizza delivery for the day of the study or the 
following day. 
2. Reside in select postcode areas in Liverpool, Manchester or Birmingham 
a. Manchester: M1, M2, M3, M4, M5, M11, M12, M13, M14, M15, M16, M18, 
M19 
b. Liverpool: L1, L2, L3, L4, L5, L6, L8, L13, L15 
c. Birmingham: B9, B10, B11, B12, B13, B25, B26, B27, B28, B33, B90, B91, 
B92 
3. Over the age of 18 
4. Have used food delivery services in the last year 
5. Are not partaking in a fast or other restrictive eating (e.g. for religious or health 
reasons) at time of participation  
6. You have no previous or current diagnosis of an eating disorder 
7. Are not on appetite-supressing medication 
8. Have none of the following dietary restrictions/intolerances:  
a. Gluten-free 
b. Dairy-free 
c. Sugar-free 
 
Do I have to take part? 
No. Participation in this research is completely voluntary. You are free to withdraw 
at any time without explanation and without incurring a disadvantage. 
 
What will happen if I take part? 

21 
 
You will complete a screening questionnaire to confirm you are eligible to take part 
and are happy with the study process. You will complete a short food choice task 
where you will select a meal to order for yourself, or on behalf of the adults in your 
household. You will be asked to report the number of adults in your household and 
their email addresses so they can also take part in the study as participants. You 
will then place your selected food order through the Tops Pizza website and 
schedule this order for delivery the same day or the following day. You will be 
asked to upload evidence of this food order (a screenshot of the order 
confirmation or receipt).  
The following day, you and the other adults in your household will be asked to 
complete a short follow-up questionnaire and select a method of financial 
reimbursement for your participation. All adults who take part in the study and 
complete the follow-up questionnaire will be reimbursed £15 each, via a bank 
transfer (estimated to be 3-5 weeks) or gift voucher (received within 2 working days 
– Amazon or JustEat).  
So that your awareness of the study hypotheses does not affect your behaviour in 
the study we provide more detailed information about the study aims at the end of 
the study. If you feel uncomfortable about this then you are free not to participate 
in this study. Overall, the online aspects of the study will take 10-15 minutes. 
 
How will my data be used? 
The University processes personal data as part of its research and teaching 
activities in accordance with the lawful basis of ‘public task’, and in accordance 
with the University’s purpose of advancing education, learning and research for 
the public benefit. University of Liverpool employee Victoria Heath 
(V.Heath@liverpool.ac.uk) acts as the Data Protection Officer for this study and 
any queries relating to the handling of your personal data can be sent to her. 
Further information on how your data will be used can be found in the table below. 
How will my data be collected? 
Through an online questionnaire and online tasks. 
How will my data be stored? 
On a password protected computer server. 
How long will my data be stored for? 
Your personal data will be stored for up to 28 days and 
then deleted. All other information will be stored 
indefinitely. 
What measures are in place to protect the 
security and confidentiality of my data? 
We will store all data on password protected computer 
servers and we never share any of your personal data 
outside of the research team for this project.  
Will my data be anonymised? 
After the study your personal information will be stored 
separately from your other questionnaire responses to 
create an anonymised data set. After 28 days all personal 
information will be deleted, but up to this point you can 
contact us and ask to see your information or have it 
deleted. 
How will my data be used? 
Your anonymised data will be combined with other 
participants’ data in order to be analysed. 
Who will have access to my data? 
The research team for this project will have access to your 
data. 

22 
 
  
 
Are there any risks in taking part? 
There are no anticipated risks to you if you take part in the study. 
 
Are there any benefits in taking part? 
There are no direct benefits, other than the monetary reimbursement you will 
receive. 
 
What will happen to the results of the study? 
We intend to publish the results from this study in a scientific journal. However, as 
explained above any personal information you provide is deleted before this and 
you would therefore not be identifiable in report. If you are interested in the results 
of the study, please let us know and we will share the results of the study with you 
when we publish it. 
 
What will happen if I want to stop taking part? 
You are under no obligation to take part in this study; it is completely your choice. 
If you do decide to take part, you are free to withdraw at any time and without 
giving any reason or explanation. Data collected up until the period you withdraw 
may be used, but only if you are happy for this to be done. Otherwise you may 
request that your data be destroyed and no further use is made of them. 
 
What if I am unhappy or if there is a problem? 
If you are unhappy, or if there is a problem, please feel free to let us know by 
contacting Amy Finlay or Eric Robinson (contact details below) and we will try to 
help. If you remain unhappy or have a complaint which you feel you cannot come to 
us with then you should contact the Research Governance Officer on 0151 794 
8290 (ethics@liv.ac.uk). Please provide details of the name or description of the 
study (so that it can be identified), the researcher(s) involved, and the details of the 
complaint you wish to make. 
 
Who can I contact if I have further questions? 
Please contact the lead researcher:  
Amy Finlay 
2.79, Eleanor Rathbone Building 
Bedford Street South 
University of Liverpool, 
Will my data be archived for use in other 
research projects in the future? 
After the research team have anonymised your data and 
completed this research project, they will place the 
anonymised data sets on an archive (e.g. Open Science 
Framework) in case any other researchers want to use it 
for future research purposes.  
How will my data be destroyed? 
Your personal data will be destroyed electronically 
(deleting the files and removing them from the computer 
server).  

23 
 
Liverpool,  
L69 7ZA, 
UK 
email: a.finlay@liverpool.ac.uk 
 
or the principal investigator 
Prof. Eric Robinson 
email: robinsoe@liverpool.ac.uk  
 
I confirm I have read the information sheet 
 
o Yes 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

24 
 
Appendix D: Participant information sheet for additional participants 
 
Health beliefs and food delivery study 
 
You are invited to participate in a research study. Before you decide whether 
to participate, it is important for you to understand why the research is being 
done and what it will involve. Please take time to read the following 
information carefully and feel free to ask us if you would like more 
information or if there is anything that you do not understand. We would like 
to stress that you should only agree to take part if you want to. 
 
What is the purpose of the study? 
The purpose of the study is to understand consumer habits when ordering pizza for 
delivery. 
  
Why have I been chosen to take part? 
We are recruiting volunteers who fulfil the following criteria: 
1. Have a household member who participated in the first part of the study 
2. Consumed food ordered in the first part of the study (A meal ordered from 
Tops pizza) 
3. Over the age of 18 
4. Are not partaking in a fast or other restrictive eating (e.g. for religious or health 
reasons) at time of participation  
5. You have no previous or current diagnosis of an eating disorder 
6. Are not on appetite-supressing medication 
7. Have none of the following dietary restrictions/intolerances:  
a. Gluten-free 
b. Dairy-free 
c. Sugar-free 
 
Do I have to take part? 
No. Participation in this research is completely voluntary. You are free to withdraw 
at any time without explanation and without incurring a disadvantage. 
 
What will happen if I take part? 
You will be required to complete a short questionnaire where you will answer 
questions relating to demographic characteristics and our stud outcomes. You will 
be asked to report what you consumed of the food order placed in part one of the 
study. Finally, you will be asked to select your preferred method of study 
reimbursement (£15 via bank transfer (slightly delayed payment) or gift voucher 
(received within 2 working days). So that your awareness of the study hypotheses 

25 
 
does not affect your behaviour in the study we provide more detailed information 
about the study aims at the end of the study. If you feel uncomfortable about this 
then you are free not to participate in this study. The study should take 5-10 
minutes to complete.  
 
How will my data be used? 
The University processes personal data as part of its research and teaching 
activities in accordance with the lawful basis of ‘public task’, and in accordance 
with the University’s purpose of advancing education, learning and research for 
the public benefit. University of Liverpool employee Victoria Heath 
(V.Heath@liverpool.ac.uk) acts as the Data Protection Officer for this study and 
any queries relating to the handling of your personal data can be sent to her. 
Further information on how your data will be used can be found in the table below. 
  
 
Are there any risks in taking part? 
There are no anticipated risks to you if you take part in the study. 
 
Are there any benefits in taking part? 
There are no direct benefits, other than the small monetary payment. 
How will my data be collected? 
Through an online questionnaire and online tasks. 
How will my data be stored? 
On a password protected computer server. 
How long will my data be stored for? 
Your personal data will be stored for up to 28 days and 
then deleted. All other information will be stored 
indefinitely. 
What measures are in place to protect the 
security and confidentiality of my data? 
We will store all data on password protected computer 
servers and we never share any of your personal data 
outside of the research team for this project.  
Will my data be anonymised? 
After the study your personal information will be stored 
separately from your other questionnaire responses to 
create an anonymised data set. After 28 days all personal 
information will be deleted, but up to this point you can 
contact us and ask to see your information or have it 
deleted. 
How will my data be used? 
Your anonymised data will be combined with other 
participants’ data in order to be analysed. 
Who will have access to my data? 
The research team for this project will have access to your 
data. 
Will my data be archived for use in other 
research projects in the future? 
After the research team have anonymised your data and 
completed this research project, they will place the 
anonymised data sets on an archive (e.g. Open Science 
Framework) in case any other researchers want to use it 
for future research purposes.  
How will my data be destroyed? 
Your personal data will be destroyed electronically 
(deleting the files and removing them from the computer 
server).  

26 
 
 
What will happen to the results of the study? 
We intend to publish the results from this study in a scientific journal. However, as 
explained above any personal information you provide is deleted before this and 
you would therefore not be identifiable in report. If you are interested in the results 
of the study, please let us know and we will share the results of the study with you 
when we publish it. 
 
What will happen if I want to stop taking part? 
You are under no obligation to take part in this study; it is completely your choice. 
If you do decide to take part, you are free to withdraw at any time and without 
giving any reason or explanation. Data collected up until the period you withdraw 
may be used, but only if you are happy for this to be done. Otherwise you may 
request that your data be destroyed and no further use is made of them. 
 
What if I am unhappy or if there is a problem? 
If you are unhappy, or if there is a problem, please feel free to let us know by 
contacting Amy Finlay or Eric Robinson (contact details below) and we will try to 
help. If you remain unhappy or have a complaint which you feel you cannot come to 
us with then you should contact the Research Governance Officer on 0151 794 
8290 (ethics@liv.ac.uk). Please provide details of the name or description of the 
study (so that it can be identified), the researcher(s) involved, and the details of the 
complaint you wish to make. 
 
Who can I contact if I have further questions? 
Please contact the lead researcher:  
Amy Finlay 
2.79, Eleanor Rathbone Building 
Bedford Street South 
University of Liverpool, 
Liverpool,  
L69 7ZA, 
UK 
email: a.finlay@liverpool.ac.uk 
 
or the principal investigator: 
Prof. Eric Robinson 
email: robinsoe@liverpool.ac.uk  
 
I confirm I have read the information sheet 
 
o Yes 
 
 
 
 

27 
 
Appendix E: Consent form for original participant  
 
 
Pizza delivery study 
I confirm that I have read and understood the information sheet for the above study. I 
have had the opportunity to consider the information, ask questions and have had these 
answered satisfactorily.  
I understand that taking part in the study involves completing online tasks and 
questionnaires. As part of this study, I will schedule and pay for a meal from a pizza 
delivery outlet. 
I understand that my participation is voluntary and that I am free to stop taking part and 
can withdraw from the study at any time without giving and reason and without my 
rights being affected. I also understand that I have the right to lodge a complaint.  
I understand that the information I provide is for research purposes and it will be held 
securely in line with the data protection requirements at the University of Liverpool. In 
addition, I understand personal information collected about me that can identify me 
will never be shared beyond the study team.  
I understand that shortly after completing the study, researchers will keep my personal 
data and store it separately from my other questionnaire responses for up to 28 days on 
a computer, so that my anonymised questionnaire responses can later be deposited in 
an online data archive for sharing and used by other authorised researchers to support 
research in the future.  
I provide my consent as a legal basis for the processing of my data as detailed 
previously, including the purposes of data processing, recipients of data and the right to 
withdraw my data. 
I agree to the above, and consent to take part in the study 
o Yes 
 
By taking part in this study, you confirm you are happy to order and pay for a meal from a 
pizza outlet for delivery. Depending on your preferred payment method, you may not be 
reimbursed for your study participation for up to 5 weeks (i.e. if bank transfer selected).  
I acknowledge the study processes and confirm to take part in the study  
o Yes 
o No 

28 
 
Appendix F: Consent form for additional participants  
 
 
Pizza delivery study 
I confirm that I have read and understood the information sheet for the above study. I 
have had the opportunity to consider the information, ask questions and have had these 
answered satisfactorily.  
I understand that taking part in the study involves completing online tasks and 
questionnaires.  
I understand that my participation is voluntary and that I am free to stop taking part and 
can withdraw from the study at any time without giving and reason and without my 
rights being affected. I also understand that I have the right to lodge a complaint.  
I understand that the information I provide is for research purposes and it will be held 
securely in line with the data protection requirements at the University of Liverpool. In 
addition, I understand personal information collected about me that can identify me 
will never be shared beyond the study team.  
I understand that shortly after completing the study, researchers will keep my personal 
data and store it separately from my other questionnaire responses for up to 28 days on 
a computer, so that my anonymised questionnaire responses can later be deposited in 
an online data archive for sharing and used by other authorised researchers to support 
research in the future.  
I provide my consent as a legal basis for the processing of my data as detailed 
previously, including the purposes of data processing, recipients of data and the right to 
withdraw my data. 
I agree to the above, and consent to take part in the study 
o Yes 
 
 
 
 
 
 

29 
 
Appendix G: Screening questionnaire  
1. Please select the postcode district where you live, and where your pizza order will be 
delivered to.  
[dropdown list of the following postcode areas: L1, L2, L3, L4, L5, L6, L8, L13, L15, M1, 
M2, M3, M4, M5, M11, M12, M14, M15, M16, M18, M19, B9, B10, B11, B12, B13, B25, 
B26, B27, B28, B33, B90, B91, B92, my postcode is not in this list] 
2. Are you able to order and pay for food from a takeaway pizza outlet (Tops Pizza) to be 
scheduled for delivery today or tomorrow? 
o Yes 
o No 
 
3. Please select your age 
 
[dropdown list 18-99] 
 
4. How frequently do you use food delivery services? (for example, JustEat, Deliveroo, or 
online ordering from a specific food business) 
o Not in the last year 
o Less than once per month 
o 1-3 times per month  
o 1-2 times per week 
o 3 times per week or more 
5. Are you currently fasting or taking part in other restrictive eating (e.g. for religious 
or health reasons)?  
o Yes 
o No 
 
6. Have you ever been diagnosed with an eating disorder? 
o Yes 
o No 
 
7. Are you currently on medication that supresses your appetite? 
o Yes 
o No 
 
8. Do you have any of the following dietary restrictions/intolerances? 
o Gluten-free 
o Dairy-free 
o Sugar-free 
o None of the above  
 
9. Do you, or any other adults you are ordering on behalf of have a food allergy?  
o Yes 

30 
 
o No 
**If Yes** 
Please be aware of the risks of ordering food prepared out of the home for people with 
food allergies. The risks involved in this study are no higher than eating out of the home 
generally. However, please consider this risk before continuing with the study.  
 
Please inform the outlet of any food allergies when you place your order.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

31 
 
Appendix H: Food ordering task instructions.  
Before the task begins: 
“We would like you to select a meal from a UK chain pizza outlet (Tops Pizza) 
using a recorded ordering platform. You can select this meal for yourself, or on 
behalf of all adults in your household.  
 
After your selection, you will place the recorded order through the Tops Pizza 
website. This order can be scheduled for today or tomorrow and must be paid for 
today. 
On the next page you will be transferred to the recorded ordering platform where you 
can look through different options. Once you select an item, you will be asked to select 
any preferences and confirm your choices.” 
 
Once Food order has been selected: 
Please report the number of adults in your household who will be eating some of 
the food ordered: 
[dropdown list 1-10] 
***new page*** 
Are you ordering this food for later today or tomorrow?  
o Later today 
o Tomorrow 
Please report the age, gender and email addresses of all the adults in your 
household (with their consent) including yourself so you can all take part in the 
study as participants. Any adult participants who have eaten some of the ordered meal 
and complete the follow up questionnaire will be financially reimbursed for their 
participation.  
However, if you do not provide correct email addresses, other household members will 
not have the opportunity to complete the follow up questionnaire, and we will not be 
able to provide reimbursement for these household members.  
[textboxes provided, the number of textboxes will be the same number of adults 
reported above] 
***new page*** 
Please now place the following order through the Tops Pizza website by opening 
this link in a new tab https://topspizza.co.uk/ 

32 
 
Please note that individual menu item and overall prices may be slightly different to 
those listed in the completed task. You will need to upload evidence of your order (a 
screenshot of the order confirmation or the receipt) so researchers can validate your 
participation.  
Your order on the Tops website must match your order made earlier to receive 
reimbursement, unless there is a reasonable explanation (i.e. if an item is not available). 
If this is the case, please provide evidence such as a screenshot. This can be sent to 
foodresearch@liverpool.ac.uk. 
When you have placed your order, please screenshot your order confirmation and save 
as a picture on your device. Return to this page.  
[List items selected] 
[In control condition, note discount code available] 
 
Please upload evidence of your food order through the Tops Pizza website. This 
confirmation should look like the example image below.  
[example image of order confirmation] 
[button to upload an image] 
 
Is the order you placed from Tops Pizza different to the order you selected in the 
online task? 
o Yes 
o No 
*if No* 
Please describe why your order from Tops Pizza differs to the order you initially 
selected in the online task. 
 
 
 
 
 

33 
 
Thank you for placing your food order. The day after your food order has been delivered, 
you and the other adults in your household will receive a link via email to complete the 
follow up questionnaire with instructions to receive study payment.  
Please contact the research team if you or other adults in the household do not receive 
an email the day after your food order: foodresearch@liverpool.ac.uk 
Enjoy your meal! 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

34 
 
Appendix I: Follow-up questionnaire 
*email sent to original participants* 
Thank you for your continued participation in our health beliefs and food delivery study! 
We hope you enjoyed your meal yesterday. Please follow the link to complete a short 
follow-up questionnaire. At the end of this questionnaire, you will be able to select your 
study reimbursement preference.  
When prompted, please input the following unique participant code into the 
questionnaire: [insert unique code] 
[insert link to questionnaire] 
*email sent to participants joining the study* 
Thank you for agreeing to take part in our health beliefs and food delivery study! Please 
follow the link to complete a short questionnaire. Before starting the questionnaire, you 
will be asked to read a study information sheet and consent form before consenting to 
take part in the study. At the end of this questionnaire, you will be able to select your 
study reimbursement preference. 
When prompted, please input the following unique participant code into the 
questionnaire: [insert unique code] 
[insert link to questionnaire] 
******************************************************* 
1. Please confirm your participant code (this is the code sent to you via email) 
 
_______________________________________ 
 
2. Please select if you would like us to hold onto your email address so you can be 
invited to take part in future research led by individuals at the University of 
Liverpool. If you select yes, your email will remain on our system for three years, 
after which it will be permanently deleted. 
o Yes 
o No 
 
3. Please think about the meal you ate yesterday. Did you eat anything from the 
following categories:  
Pizzas   
 
 
Yes ☐  
 
No ☐ 
Starters/Side dishes   
Yes ☐  
 
No ☐ 

35 
 
Desserts  
 
 
Yes ☐  
 
No ☐ 
Drinks   
 
 
Yes ☐  
 
No ☐ 
Dips   
 
 
Yes ☐  
 
No ☐ 
**If yes for Pizzas** 
Please select a pizza that you ate last night [dropdown list of all pizzas] 
How many slices of this pizza did you eat? [dropdown list of number of possible slices, 
and ‘full pizza’].  
Did you eat another pizza? [dropdown Yes/No] 
**if Yes, repeat above** 
 
**if Yes for other categories, for example Starters/Side dishes** 
Please select a Starter/Side dish that you ate last night [dropdown list of all starters/side 
dishes] 
Approximately how much of this Starter/Side dish did you eat? [dropdown list: 25%, 
50%, 75%, 100%] 
Did you eat another Starter/Side dish? [dropdown Yes/No] 
**if Yes, repeat above** 
 
4. [insert health beliefs scale] – scale is currently under development. 
 
5. Gender 
- 
Man 
- 
Woman 
- 
Other 
6. Age:  
*dropdown list: 18 – 99* 
 
7. Ethnicity (Choose one option that best describes your ethnic group or 
background) 
*dropdown list:  
White English/Welsh/Scottish/Northern Irish/British 
White Irish 

36 
 
Any other White background 
White and Black Caribbean 
White and Black African 
Any other mixed/multiple ethnic background please describe  
Indian 
Pakistani 
Bangladeshi 
Chinese 
Other Asian 
African 
Caribbean 
Arab 
Any other ethnic group 
 
8. What is your height?  
__ ft __ in 
OR  
___cm 
 
9. What is your weight? 
__ st __ lb 
OR 
___kg 
 
 
10. What is your highest educational qualification? If you are a student please 
select the diploma being studied for. 
o Less than high-school or equivalent (i.e. 1-4 GCSEs or O levels, 
foundation diploma) 
o High-school completion or equivalent (i.e. 5+ GCSEs/O levels, Scottish 
Higher, Scottish advanced higher, intermediate/higher diploma) 
o College or foundation degree or equivalent (i.e. apprenticeships, A-levels, 
progression/advanced diploma) 
o Bachelor’s degree 
o Master’s degree 
o Doctoral or professional degree 

37 
 
 
11. What is your annual household income (after tax), including all earners in your 
household, in GBP (to the nearest £1000)?  
____________ 
12. How many people live at your house, including you? 
___ adult(s) or child(ren) aged 14 and over  
___ child(ren) aged under 14  
13. Think of a ladder (see image) as representing 
where people stand in society. At the top of the 
ladder are the people who are best off—those who 
have the most money, most education and the 
best jobs. At the bottom are the people who are 
worst off—who have the least money, least 
education and the worst jobs or no job. The higher 
up you are on this ladder, the closer you are to 
people at the very top and the lower you are, the 
closer you are to the bottom. Where would you 
place yourself on the ladder?  
 
Choose the number whose position best represents 
where you would be on this ladder: 
*dropdown list: 1 – 10* 
 
14. This is an attention check. How many times have you visited the planet 
Mars? 
o Several times 
o Just once 
o Never 
 
15. How often, on average over the past year have you eaten takeaway pizza? 
o Not in the last year 
o Less than once per month 
o 1-3 times per month 
o 1-2 times per week 
o 3 times per week or more 
 

38 
 
16. [food choice motives questionnaire]  
Several different factors influence our choice of food. Read each item carefully 
and decide how important the item is to you. There are no right or wrong 
answers, we are interested in what is important to you. 
It is important to me that the food I eat on a typical day… 
 
FCM 
no. 
 
Not at all 
important 
1 
A little 
important 
2 
Moderately 
important 
3 
Very 
important 
4 
1 
Is easy to prepare 
o 
 
o 
 
o 
 
o 
 
4 
Tastes good 
o 
 
o 
 
o 
 
o 
 
6 
Is not expensive 
o 
 
o 
 
o 
 
o 
 
9 
Is high in fibre and roughage 
o 
 
o 
 
o 
 
o 
 
10 
Is nutritious 
o 
 
o 
 
o 
 
o 
 
11 
Is easily available in shops and supermarkets 
o 
 
o 
 
o 
 
o 
 
12 
Is good value for money 
o 
 
o 
 
o 
 
o 
 
14 
Smells nice 
o 
 
o 
 
o 
 
o 
 
 
This is an attention check.  
Please select the answer (2) ‘A little important’ 
o 
 
o 
 
o 
 
o 
 
15 
Can be cooked very simply 
o 
 
o 
 
o 
 
o 
 
18 
Has a pleasant texture 
o 
 
o 
 
o 
 
o 
 
22 
Contains a lot of vitamins and minerals 
o 
 
o 
 
o 
 
o 
 
25 
Looks nice 
o 
 
o 
 
o 
 
o 
 
27 
Is high in protein 
o 
 
o 
 
o 
 
o 
 
28 
Takes no time to prepare 
o 
 
o 
 
o 
 
o 
 
29 
Keeps me healthy 
o 
 
o 
 
o 
 
o 
 
30 
Is good for my skin/teeth/hair/nails etc. 
o 
 
o 
 
o 
 
o 
 
35 
Can be bought in shops close to where I live or work 
o 
 
o 
 
o 
 
o 
 
36 
Is cheap 
o 
 
o 
 
o 
 
o 
 
 
17. UPPS-P subscales 
Please select how much you agree with each statement using the response scale 
below:  
1. When I feel bad, I will often do things I later regret in order to make myself feel 
better now.  
 
1 = Strongly agree 
2 = Agree 
3 = Disagree 
4 = Strongly disagree 
 
2. Sometimes when I feel bad, I can’t seem to stop what I am doing even though it 
is making me feel worse.  
 
1 = Strongly agree 
2 = Agree 

39 
 
3 = Disagree 
4 = Strongly disagree 
 
3. When I am upset, I often act without thinking.  
 
1 = Strongly agree 
2 = Agree 
3 = Disagree 
4 = Strongly disagree 
 
4. When I feel rejected, I will often say things that I later regret.  
 
1 = Strongly agree 
2 = Agree 
3 = Disagree 
4 = Strongly disagree 
 
5. My thinking is usually careful and purposeful.  
 
1 = Strongly agree 
2 = Agree 
3 = Disagree 
4 = Strongly disagree 
 
6. I like to stop and think things over before I do them.  
 
1 = Strongly agree 
2 = Agree 
3 = Disagree 
4 = Strongly disagree 
 
7. I tend to value and follow a rational, sensible approach to things.  
 
1 = Strongly agree 
2 = Agree 
3 = Disagree 
4 = Strongly disagree 
 
8. I usually think carefully before doing anything.  
 
1 = Strongly agree 

40 
 
2 = Agree 
3 = Disagree 
4 = Strongly disagree 
 
9. When I am in a great mood, I tend to get into situations that could cause me 
problems.  
 
1 = Strongly agree 
2 = Agree 
3 = Disagree 
4 = Strongly disagree 
 
10. I tend to lose control when I am in a great mood.  
 
1 = Strongly agree 
2 = Agree 
3 = Disagree 
4 = Strongly disagree 
 
11. Others are shocked or worried about the things I do when I am feeling very 
excited.  
 
1 = Strongly agree 
2 = Agree 
3 = Disagree 
4 = Strongly disagree 
 
12. I tend to act without thinking when I am really excited.  
 
1 = Strongly agree 
2 = Agree 
3 = Disagree 
4 = Strongly disagree 
 
18. What do you think the aim of the study was? 
________________________________________________________ 
________________________________________________________ 
[Subset 1: RAND order questions 13, 14 & 15] 

41 
 
19. To what extent do you think product price incentives (e.g. 25% off all menu 
items/size up for £1/meal deal and bundle options) on unhealthy food saves 
you money in the out-of-home food sector? 
o  
o  
o  
o  
o  
o  
o  
Strongly 
disagree 
Disagree 
Slightly 
disagree 
Neither 
agree or 
disagree 
Slightly 
agree 
Agree 
Strongly 
agree 
 
20. To what extent do you think product price promotions (e.g. 25% off all menu 
items/size up for £1/meal deal and bundle options) lead you to purchase 
more unhealthy food in the out-of-home food sector? 
 
 
21. To what extent do would you agree with the government banning price 
incentives (e.g. 25% off all menu items/size up for £1/meal deal and bundle 
options) on unhealthy food (but not healthy food) in the out-of-home food 
sector to promote healthier eating?  
 
 
22. Please report the number of children (<18 years) in your household ate some 
of the purchased food:  
o No children  
o 1 child 
o 2 children  
o 3+ children 
 
23. Please estimate the amount that each child ate in as much detail as you did 
for yourself: 
e.g.  
Child 1: 1 slice of Large BBQ chicken pizza, 1 slice of garlic bread with cheese, 25% of 
garlic and herb dip 
Child 2: 1 slice of Medium Margherita pizza, 30% of potato wedges portion, 1 can of 
Fanta 
o  
o  
o  
o  
o  
o  
o  
Strongly 
disagree 
Disagree 
Slightly 
disagree 
Neither 
agree or 
disagree 
Slightly 
agree 
Agree 
Strongly 
agree 
o  
o  
o  
o  
o  
o  
o  
Strongly 
disagree 
Disagree 
Slightly 
disagree 
Neither 
agree or 
disagree 
Slightly 
agree 
Agree 
Strongly 
agree 

42 
 
 
 
 
 
 
 
24. Please state any thoughts you have that have not been covered in the 
questionnaire: 
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________ 
 
************* 
Please select your preferred method of study payment. A researcher will be in touch to 
ask for bank details if bank transfer is your preferred payment method.  
o £15 bank transfer (can take up to 5 weeks to appear in account) 
o £15 JustEat Voucher (typically received within 2 working days) 
o £15 Amazon voucher (typically received within 2 working days) 
 
 
 
 
 
 
 
 
 
 
 
 
 

43 
 
Appendix J: Debriefing text 
In this study we were interested in the effect of price-based incentives on food choices 
in the out-of-home food sector. 
All participants who initially signed up to the study and placed food orders were 
presented with the same food choices with one of two pricing conditions.  
- 
In the first condition, participants were provided with the Tops pizza menu as it 
exists currently, with three different types of price-based incentives:  
o Product price promotions (discount code for £ [insert code details]) 
o Bulk buy reductions (meal deals/bundles) 
o Volume value pricing (size increase for a very small price difference) 
- 
In the second condition, participants were provided with a menu with no price-
based incentives. 
We wanted individuals to place real food orders so that the intervention would have 
real-life consequences.   
We will compare if people order, pay for and consume more food when price incentives 
for less healthy food options are available, as well as whether participant 
characteristics shape these relationships. The results will help to assess the potential 
impact of limiting the type of price-based incentives on unhealthy food that businesses 
can use in the out-of-home food sector.  
If this study has raised any issues regarding your weight or eating behaviours, we 
recommend contacting your doctor. The following NHS page provides information and 
guidance on eating a healthy, balanced diet: https://www.nhs.uk/live-well/eat-well/ 
Thank you very much for your participation in our study.