Effectiveness of Information-based Versus Structural Interventions on Food Choices by Socioeconomic Position: a Randomized Controlled Trial in an Experimental Online Supermarket
Phase: NA
Conditions: Diet, Healthy, Food Selection
Sponsor: University of Liverpool

07/04/2020, pre-registered 
1 
ED and SEP Online Supermarket Study 
STUDY PROTOCOL 
Study title: Effectiveness of information-based versus structural interventions on food choices by 
socioeconomic position: a randomized controlled trial in an experimental online supermarket 
Short title: ED and SEP Online Supermarket Study 
Investigators from University of Liverpool: 
Dr Lucile Marty 
Dr Andrew Jones 
Dr Eric Robinson 
Investigators from Oxford: 
Professor Susan Jebb 
Dr Carmen Piernas 
Dr Brian Cook 
Funder: European Research Council 
 
 

07/04/2020, pre-registered 
2 
ED and SEP Online Supermarket Study 
TABLE OF CONTENTS 
 
1. 
BACKGROUND AND RATIONALE .................................................................................................... 3 
2. 
OBJECTIVES, OUTCOMES MEASURES AND HYPOTHESES ............................................................. 3 
3. 
EXPERIMENTAL DESIGN ................................................................................................................. 4 
4. 
PARTICIPANTS AND RECRUITMENT ............................................................................................... 4 
4.1. 
Recruitment ............................................................................................................................ 4 
4.2. 
Inclusion criteria ..................................................................................................................... 5 
4.3. 
Exclusion criteria .................................................................................................................... 5 
5. 
METHODS ....................................................................................................................................... 6 
5.1. 
Online shopping task .............................................................................................................. 6 
5.2. 
Measures of socioeconomic position .................................................................................... 8 
5.3. 
Measure of health and weight control food choice motives ................................................ 8 
6. 
STUDY FLOW ................................................................................................................................... 8 
7. 
STATISTICAL ANALYSIS ................................................................................................................... 9 
7.1. 
Definition of population for analysis ..................................................................................... 9 
7.2. 
Participant’s characteristics ................................................................................................... 9 
7.3. 
Description of variables ......................................................................................................... 9 
7.4. 
Missing data ......................................................................................................................... 11 
7.8. 
Sample size ........................................................................................................................... 13 
REFERENCES .......................................................................................................................................... 15 
APPENDIX A: AUDIENCE (PROLIFIC WEBSITE) ..................................................................................... 18 
APPENDIX B: RECRUITMENT TEXT ....................................................................................................... 19 
APPENDIX C: INFORMATION PAGE ...................................................................................................... 20 
APPENDIX D: CONSENT PAGE .............................................................................................................. 23 
APPENDIX E: BASELINE QUESTIONNAIRE ............................................................................................ 25 
APPENDIX F: ONLINE SHOPPING TASK INSTRUCTION ........................................................................ 29 
APPENDIX G: HEALTH AND WEIGHT CONTROL MOTIVES ................................................................... 30 
APPENDIX H: DEBRIEFING QUESTIONNAIRE ....................................................................................... 31 
APPENDIX I: DEBRIEFING TEXT ............................................................................................................ 33 
 
 
 

07/04/2020, pre-registered 
3 
ED and SEP Online Supermarket Study 
1. BACKGROUND AND RATIONALE 
People of lower socioeconomic position (SEP) are more likely to have obesity than people of higher 
SEP and SEP inequities in obesity in Europe are widening [1]. Lower socioeconomic position (SEP) is 
associated with a more energy dense diet [2], [3]. Consumption of more energy dense foods has 
been consistently linked to higher energy intake in experimental studies [4] and results from 
prospective cohort studies have shown a positive association between energy density (ED) of the 
total diet and BMI [4]. Thus, the association between SEP and obesity may be mediated, in part, by 
the consumption of a more energy-dense diet [5]. Interventions that reduce dietary energy density 
would benefit public health, particularly among people of lower SEP. 
In the UK, 26% of the adults eat meals out one or more times per week and 20% eat takeaway meals 
at home one or more times per week, suggesting that the major part of the meals consists in food 
prepared at home [6]. People from lower SEP tend to spend a greater proportion of their average 
food expenditure on prepared-at-home produce (such as products purchased in supermarkets) as 
opposed to catering services than people of higher SEP (lowest equivalised disposable income decile 
group: 74% vs. highest: 60%) [7]. Thus, nutrition interventions targeting supermarket purchases 
provide an opportunity to benefit the diet of all of the population and people of lower SEP in 
particular. 
Information-based nutrition interventions are one of the most common approaches to improving 
diet [8], [9]. An example of an information-based intervention is menu energy labelling in 
restaurants [10]. This type of interventions has been suggested to be less effective among people of 
lower compared to higher SEP [11], [12]. However, systematic reviews of the impact of menu energy 
labelling has highlighted the limited quality of evidence supporting this hypothesis [11], [13]. It has 
been suggested that structural interventions that target core features of the food environment (i.e., 
reducing portion sizes, increasing the availability of heathier food options) and require individuals to 
use a low level of agency may be most effective and most equitable [8], [14], [15]. However, there is 
a lack of empirical evidence to support this hypothesis. 
Information-based interventions typically rely on people being motivated by health in their food 
choices [16]. Yet, health may be a less influential motive for food choice among people of lower SEP 
[17]. Thus, SEP based differences in food choice motives, and notably health motivation, may explain 
why information-based interventions could be less effective among people of lower vs. higher SEP. 
The aim of this study is to examine how an information-based intervention (labelling of lower ED 
food products) and a structural intervention (greater proportion of lower ED options in food product 
ranges) affect the ED of food purchases within a virtual online supermarket [18] in participants of 
lower vs. higher SEP. The primary hypothesis is that labelling will reduce the ED of virtual online 
supermarket food purchases to a greater extent in participants of higher SEP vs. lower SEP. 
Conversely, we hypothesise that a greater proportion of lower ED options will decrease the ED of 
food purchases equally among participants of lower and higher SEP. The secondary hypothesis is 
that differences in health-based food choice motives in participants of lower vs. higher SEP will 
mediate the differential effect that ED labelling has on ED of food purchases among participants of 
lower vs. higher SEP. 
2. OBJECTIVES, OUTCOMES MEASURES AND HYPOTHESES 
OBJECTIVES 
OUTCOME MEASURES 
HYPOTHESES 
Primary objective 
 
 
 
 
 

07/04/2020, pre-registered 
4 
ED and SEP Online Supermarket Study 
To examine the effectiveness 
of an information-based 
intervention (ED labelling) and 
a structural nutrition 
intervention (greater 
proportion of lower ED 
options) on the ED of virtual 
online supermarket food 
purchases; and if this effect is 
different between participants 
of lower and higher SEP. 
 
Mean ED (kcal/100g) of foods 
purchased 
SEP will influence the effect of 
the interventions. In particular, 
ED labelling will reduce ED of 
foods purchased to a greater 
extent in participants of higher 
vs. lower SEP. Conversely, a 
greater proportion of lower ED 
options will decrease ED of 
food purchases equally among 
participants of lower and 
higher SEP. 
Secondary objectives 
 
To investigate the 
psychological processes that 
explain why an information-
based intervention (ED 
labelling) and a structural 
nutrition intervention (greater 
proportion of lower ED 
options) may have differential 
effects on ED of food 
purchases among participants 
of lower vs. higher SEP. 
 
 
Health and weight control 
food choices motives 
(questionnaire score) 
 
 
The participants of higher SEP 
will be more motivated by 
health and weight control in 
their food choices than 
participants of lower SEP, 
which will moderate the 
relationship between SEP and 
the effect of ED labelling on ED 
of foods purchased. 
 
3. EXPERIMENTAL DESIGN 
This study will be a 2x2 randomised controlled trial with information-based intervention (no labelling 
/ labelling) and structural intervention (default proportion / increased proportion of lower ED food 
items) as between-subject factors and ED (kcal/g) of food purchases during an online supermarket-
shopping task as dependent variable. 
4. PARTICIPANTS AND RECRUITMENT 
 
4.1. Recruitment 
Participants will be recruited through an online recruitment panel (Prolific) in which participants are 
compensated proportionate to the time it takes to complete the online study (≈ £5/hour reward 
participants). 
Participants’ recruitment will be stratified by gender (50% male, 50% female), student status (3.5% 
yes and 96.5% no) [19] and qualification levels; the proportion of low (below level 4) versus high 
(level 4 of above) qualification levels will be based on current population statistics from the Labour 
Force Survey (LFS) 2013 for adults aged 19-64 in England [20]: 
- 
60% lower qualification levels 
o No formal qualifications 
o 1–3 GCSEs or equivalent 

07/04/2020, pre-registered 
5 
ED and SEP Online Supermarket Study 
(Level 1: first certificate; GCSE - grades 3, 2, 1 or grades D, E, F, G; level 1 award; level 1 
certificate; level 1 diploma; level 1 ESOL; level 1 essential skills; level 1 functional skills; level 1 
national vocational qualification (NVQ); music grades 1, 2 and 3) 
o 4+ GCSEs or equivalent 
(Level 2: CSE - grade 1; GCSE - grades 9, 8, 7, 6, 5, 4 or grades A*, A, B, C; intermediate 
apprenticeship; level 2 award; level 2 certificate; level 2 diploma; level 2 ESOL; level 2 
essential skills; level 2 functional skills; level 2 national certificate; level 2 national diploma, 
level 2 NVQ; music grades 4 and 5; O level - grade A, B or C) 
o A level or equivalent 
(Level 3: A level; access to higher education diploma; advanced apprenticeship; applied 
general; AS level; international Baccalaureate diploma; level 3 award; level 3 certificate; level 
3 diploma; level 3 ESOL; level 3 national certificate; level 3 national diploma; level 3 NVQ; 
music grades 6, 7 and 8; tech level) 
 
- 
40% higher qualification levels 
o Certificate of higher education (CertHE) or equivalent 
(Level 4: certificate of higher education (CertHE); higher apprenticeship; higher national 
certificate (HNC); level 4 award; level 4 certificate; level 4 diploma; level 4 NVQ);  
o Diploma of higher education (DipHE) or equivalent 
(Level 5: diploma of higher education (DipHE); foundation degree; higher national diploma 
(HND); level 5 award; level 5 certificate; level 5 diploma; level 5 NVQ) 
o Bachelor or equivalent 
(Level 6: degree apprenticeship; degree with honours - for example bachelor of the arts (BA) 
hons, bachelor of science (BSc) hons; graduate certificate; graduate diploma; level 6 award; 
level 6 certificate; level 6 diploma; level 6 NVQ; ordinary degree without honours) 
o Master’s degree or equivalent 
(Level 7: integrated master’s degree, for example master of engineering (MEng); level 7 
award; level 7 certificate; level 7 diploma; level 7 NVQ; master’s degree, for example master 
of arts (MA), master of science (MSc); postgraduate certificate; postgraduate certificate in 
education (PGCE); postgraduate diploma) 
o Doctorate or equivalent 
(Level 8: doctorate, for example doctor of philosophy (PhD or DPhil); level 8 award; level 8 
certificate; level 8 diploma) 
 
4.2. Inclusion criteria 
 
• 
UK residents, aged ≥ 18 years 
• 
Fluent in English 
• 
Have access to a computer and Internet 
• 
Responsible for a substantial proportion of household grocery shopping 
 
4.3. Exclusion criteria 
 
• 
Unable to provide informed consent and to comply with the study requirements 
• 
Any of the following dietary restrictions: 
o Vegetarian 
o Vegan 
o Gluten-free 
o Sugar-free 
o Dairy/lactose-free 

07/04/2020, pre-registered 
6 
ED and SEP Online Supermarket Study 
o Food allergy (e.g. milk, eggs, nut, wheat, fish, etc.) 
 
5. METHODS 
 
5.1. Online shopping task 
Experimental online supermarket 
This study will use an online supermarket platform (www.woodssupermarket.co.uk) developed to 
mimic an online supermarket website [18]. As prior work has suggested it is inappropriate to 
combine food and drinks when calculating ED [21], all the drinks will be removed from the online 
supermarket. 
Shopping task 
Participants will be asked to complete a shopping task using a pre-determined shopping list of 10 
items (Table 1). 
Table 1. Description of the food shopping list. 
Food items 
Department 
Aisle 
Shelf 
Number 
of 
product
s 
Mean ED 
(min-max) 
A packet of biscuits 
Food 
Cupboard 
Biscuits & 
crackers 
Biscuits 
247 
478 (341-574) 
A standard sized 
loaf of bread  
Bakery 
Bread 
 
142 
251 (186-345) 
A chilled pizza 
Dairy, eggs & 
chilled 
Pizza, pasta 
& garlic 
bread 
Pizza 
24 
269 (221-319) 
An ice cream tub 
Frozen 
Ice cream & 
ice 
Ice cream tubs 
142 
225 (76-341) 
A chilled ready 
meal for one 
Dairy, eggs & 
chilled 
Ready meals 
Meals for one 
185 
145 (71-316) 
A pack of sausages 
Meat & fish 
Bacon & 
sausages 
Sausages 
53 
263 (145-473) 
A sharing bag of 
crisps or savoury 
snacks 
Food 
Cupboard 
Crisps, nuts 
& snacking 
fruit 
Sharing crisps 
144 
490 (397-580) 
A pre-packed piece 
of cheese 
Dairy, eggs & 
chilled 
Dairy & eggs 
Cheese 
334 
321 (59-527) 
A pack of yogurts 
Dairy, eggs & 
chilled 
Dairy & eggs 
Yogurts 
251 
87 (39-193) 
A jar of jam or 
sweet spread 
Food 
Cupboard 
Jams, honey 
& spreads 
Excluding 
‘Savoury pastes’ 
and "Marmite & 
yeast extracts 
156 
392 (139-650) 
 
These categories were chosen as representing major contributors to UK diet [22] and because in 
each category there are products with a range of EDs. 

07/04/2020, pre-registered 
7 
ED and SEP Online Supermarket Study 
Interventions 
Participants will be randomly allocated to one of the following groups: 
o default proportion & no labelling (D); 
o default proportion & labelling (DL); 
o increased proportion of lower ED food items & no labelling (I); 
o increased proportion of lower-ED food items & labelling (IL). 
The interventions will only be applied in the aisles and shelves of the online supermarket that 
include food items from the shopping list. Lower ED products will be defined in relation to a 
threshold for each aisle or shelf: lower ED ≤ median of ED distribution within a food category. 
In the labelling conditions (DL and IL) “healthier choice” badges will be added to the food item 
pictures when the above criterion is met. For labelling conditions only, instructions when logging-
into the platform will introduce the badges to the participants: “In the online supermarket, the 
green tick allows you to see which products (e.g. muesli) in each product category (e.g. cereals) are 
healthier choices with fewer calories per gram than most other products in the same category.” The 
design of the badge is based on previous research investigating the effect of front-of-package 
nutrition labelling on food choices [23] (Figure 1). 
 
Figure 1. Healthier choice badge display in the labelling conditions when lower ED ≤ median of ED 
distribution within a food category. 
In the increased proportion of lower ED food items conditions (I and IL) the proportion of lower ED 
vs. higher ED options will be reversed (67% lower ED – 33% higher ED) relative to the default 
proportion conditions (D and DL) (33% lower ED – 67% higher ED) (Table 2). 
Table 2. Food items proportion and “healthy” labelling within a specific food category 
 
d1 
d2 
d3 
d4 
d5 
d6 
d7 
d8 
d9 
d10 
Default 
proportion 
No 
labelling 
present 
absent 
absent 
absent 
present 
absent 
present 
present 
present 
present 
Default 
proportion 
Labelling 
present 
healthy 
absent 
absent 
absent 
present 
heathy 
absent 
present 
present 
present 
present 
Increased 
proportion 
No 
labelling 
present 
present 
present 
present 
absent 
present 
absent 
absent 
absent 
present 
Increased 
proportion 
Labelling 
present 
healthy 
present 
healthy 
present 
healthy 
present 
healthy 
absent 
present 
absent 
absent 
absent 
present 
di: food items in a given food category with ED ≤ ith decile of ED distribution within this food category 
Comments on Table 1: 

07/04/2020, pre-registered 
8 
ED and SEP Online Supermarket Study 
- 
d5 or d6 is absent to create a gap between lower and higher ED options that makes 
“healthier choice” badges credible; 
- 
d1 (min) and d10 (max) remain in all conditions. 
 
5.2. Measures of socioeconomic position 
Four measures of socioeconomic position will be included. Participants will be asked to report: 
- 
their highest educational qualification; 
- 
their number of years in higher education; 
- 
their after tax household income and their household composition in order to calculate their 
equivalised disposable income [24]; 
- 
their household postcode, which will be linked to the English Index of Multiple Deprivation 
(IMD) [25] for the purpose of other research; 
- 
a subjective measure of their socioeconomic position using the MacArthur Scale of 
Subjective Social Status (SSS) [26]. 
 
5.3. Measure of health and weight control food choice motives 
We will use the ‘Health’ and ‘Weight control’ subscales from the Food Choice Questionnaire 
developed Steptoe et al. 1995 [27]. 
6. STUDY FLOW 
RECRUITMENT 
(Prolific) 
▪ 
Predefined screening questions of Prolific website will be used to 
target the sample (Appendix A) 
▪ 
Participants who will meet the inclusion/exclusion criteria will be 
e-mailed by Prolific and/or will be offered to complete our study 
on their Prolific account (Appendix B) 
▪ 
Eligible participants who want to take part on the study will click 
on the start button and be redirected to our study website 
INFORMED CONSENT 
(Qualtrics) 
▪ 
Participants will read the information sheet (Appendix C) 
▪ 
Participants who want to proceed will tick a consent box 
(Appendix D) 
▪ 
Participants will be allowed to contact the investigator via the 
“Contact researcher” button on Prolific webpage 
BASELINE 
ASSESSMENTS 
(Qualtrics) 
▪ 
Participants will complete a baseline questionnaire on 
demographic, grocery shopping and health data (Appendix E) 
RANDOMISATION 
(Qualtrics) 
▪ 
Participants will be randomly allocated to one of the four 
experimental conditions; same number of participants in each of 
the four groups. 
Default 
proportion & 
no labelling 
(D) 
Default 
proportion & 
labelling 
(DL) 
Increased 
proportion & 
no labelling 
(I) 
Increased 
proportion & 
labelling 
(IL) 
ONLINE SHOPPING 
TASK 
(Woods) 
▪ 
Instructions will be displayed (Appendix F) 
▪ 
The shopping list will be displayed and participants will do the 
shopping task. 
HEALTH AND WEIGHT 
CONTROL MOTIVES 
(Qualtrics) 
▪ 
Health and weight control food choice motives will be assessed – 
questions will be randomised (Appendix G) 

07/04/2020, pre-registered 
9 
ED and SEP Online Supermarket Study 
DEBRIEFING 
(Qualtrics) 
▪ 
Aim guessing in an open-ended response format 
▪ 
Insight on the participants’ perception of the online shopping 
task (Appendix H) 
▪ 
Text to tell the participants what the study was about (Appendix 
I) 
 
7. STATISTICAL ANALYSIS 
All statistical analyses will be performed using SAS version 9.3 (SAS Institute, Inc., 2012 SAS® 9.3. 
Cary, NC). The level of significance will be set at p < 0.05 for primary and sensitivity analyses and at p 
< 0.01 for secondary analyses. 
7.1. Definition of population for analysis 
Only participants who have completed the entire study (i.e., baseline assessments + online shopping 
task + questionnaires) will be included in the analysis. Participants who will have failed at least one 
attention check or have not complied with the shopping task will be excluded. 
Two attention checks will be included: 
- 
In the baseline questionnaire, item 9: This is an attention check. How many times have you 
visited the planet Mars? Several times / Just once / Never. Correct answer: Never 
- 
In the food choice questionnaire, item 7: This is an attention check. Please choose the 
answer 2 ‘Not important’. Correct answer: 2 ‘Not important’. 
We will analyse data from participants who bought at least 5 items out of 10 categories of the 
shopping list  and, if participants buy more than the 10 items requested, as in previous research we 
will include all items bought [28], [29]. Outcome measures will be based on all the foods in the 
shopping baskets. 
7.2. Participant’s characteristics 
A table will present the baseline characteristics by condition group and overall. The table will include 
gender, age, ethnic group, proportion of students, highest educational qualification, years in higher 
education, equivalised household income, subjective socioeconomic position, BMI, dieting status, 
grocery shopping in supermarkets frequency, grocery shopping online frequency. Continuous 
variables will be summarised using means and standard deviations. Categorical variables will be 
summarised using counts and percentages. 
7.3. Description of variables 
Primary outcome 
The main outcome variable is the mean ED of the food items purchased (kcal/100g) calculated as: 
𝑀𝑒𝑎𝑛 𝐸𝐷= ∑
𝑒𝑛𝑒𝑟𝑔𝑦𝑖
10
𝑖=1
∑
𝑤𝑒𝑖𝑔ℎ𝑡𝑖
10
𝑖=1
× 100 
with energy in kcal, weight in g and i representing each food in the shopping list. 
Secondary outcomes 
From the shopping task: 

07/04/2020, pre-registered 
10 
ED and SEP Online Supermarket Study 
- 
Total energy (kcal) of the foods purchased 
- 
Energy from total sugar (% of total energy) 
- 
Energy from saturated fatty acids (SFA) (% of total energy) 
- 
Salt content (g/100g) 
- 
Proportion of lower ED foods (as defined paragraph 5.1.) in the basket of foods purchased 
- 
Cost (£, £/100g and £/100kcal) of the foods purchased 
From the debriefing questionnaire: 
- 
Validity: mean of item “I would normally buy [the 10 items on the shopping list]” for all the 
food items coded as: 1 = Never; 2 = Very rarely; 3 = Rarely; 4 = Occasionally; 5 = Frequently; 
6 = Very frequently. 
- 
Kcal influence: answer to the item “The choices I made during online shopping were 
influenced by how many calories I thought were in the options available.” coded as: 1 = 
Strongly disagree; 2 = Disagree; 3 = Slightly disagree; 4 = Neutral; 5 = Slightly agree; 6 = 
Agree; 7 = Strongly agree 
Independent variables 
SEP 
Level of education 
- 
Highest educational qualification will be coded from 1 to 9: 1 = No formal qualifications; 2 = 
1–3 GCSEs; 3 = 4+ GCSEs; 4 = A level; 5 = Certificate of higher education (CertHE); 6 = 
Diploma of higher education (DipHE); 7 = Bachelor; 8 = Master’s degree; 9 = Doctorate, and 
as a binary variable as lower (values: 1, 2, 3, 4 ) or higher (values: 5, 6, 7, 8, 9). 
- 
Years in higher education, as a continuous variable 
- 
Level of education (composite score): In order to account for years in higher education and 
highest education qualification when characterising each participants’ education level, we 
will z-score the two variables and create an average of the two to form a composite score 
called ‘level of education’. 
Equivalised household disposable income: The OECD-modified equivalence scale will be used to 
adjust household income, taking into account household size and composition [24]. Equivalised 
income will be calculated by 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 = 0.5, 
child aged 0-13 = 0.3. 
Subjective SEP: The measure of the Subjective Social Status using the MacArthur Scale will be coded 
from 1 to 10. 
Health and weight control food choice motives 
Both health and weight control scores will be computed by averaging ratings for individual items of 
each dimension (health motivation: 6 items; weight control motivation: 4 items). Response options 
range from 1 to 4: 1 = Not at all important; 2 = A little important; 3 = Moderately important; 4 = Very 
important. Cronbach’s alpha will be calculated as an indicator of internal consistency in order to 
compare our data with the original study that developed this measure [27]. 
Other variables 

07/04/2020, pre-registered 
11 
ED and SEP Online Supermarket Study 
BMI: Self-reported height will be recalculated into height in metres (1 ft = 0.3048 m, 1 in = 0.0254 
m). Self-reported weight will be recalculated into weight in kilograms. (1 stone = 6.35029 kg, 1 lb = 
0.453592 kg). BMI will be calculated as weight (kg) / height (m2). BMI data will be trimmed for 
implausible values excluding weight for less than 30 kg and more than 250 kg, height for less than 
145 cm and more than 3m, BMI < 14 or BMI > 48 [30], [31]. 
Aim guessing: Participants who identify the aim of the study as being to examine the influence of 
labelling or increased proportion of lower ED/healthier food items on food purchases will be coded 
as being aware of the study aims. Responses will be independently coded by two researchers, with 
discrepancies in coding decisions resolved by a third researcher. 
7.4. Missing data 
We do not anticipate missing data for analysis of the primary outcome for the population because 
ED is calculated based on the food database embedded in the online supermarket platform. We do 
not anticipate missing data either for the dependant variables because the questionnaires will not 
allow missing answers. Data from participants who start but not finish the study will not be included. 
Any a posteriori withdrawal will be reported and reasons for withdrawal will be documented (e.g., 
incorrect answers, technical problems). 
7.5. Primary analyses 
The measure of SEP used in our primary analysis will be the level of education because previous 
research showed that people of higher education were more likely to use nutrition labels [32], [33]. 
ANCOVA will be used to test the effect of labelling (categorical variable: yes or no), proportion 
(categorical variable: default or increased), level of education (continuous variable) and 
labelling*level of education and proportion*level of education interactions on the mean ED of foods 
purchased. If this analysis reveals the predicted significant interaction between labelling or 
proportion condition and the continuous measure of level of education on mean ED, we will further 
examine the nature of the interactions by conducting floodlight analysis [34]. We will calculate the 
Johnson–Neyman point defined as the value of educational level for which the effect of labelling (or 
proportion) reaches statistical significance [35]. Values of level of education above this point will 
correspond to significant differences between the labelling and no labelling conditions (resp. the 
default and increased proportion conditions) whereas values below the point will not. The floodlight 
analysis will be run using the SAS macro developed by Hayes & Matthes, 2009 [36]. 
7.6. Sensitivity analyses 
Sensitivity analyses will be conducted to examine whether the pattern of results from the primary 
analyses differ after excluding participants guessing the aims of the study. 
We will repeat our main analyses with a more stringent criteria for having completed the shopping 
task as intended (excluding any participants who did not select 10 items in total and 1 item from 
each category on the shopping list). 
We will also repeat the main analysis substituting the composite variable level of education by years 
in higher education as a continuous covariate (ANCOVA) and by highest educational qualification 
split into lower vs. higher qualification levels as a binary covariate (2x2x2 ANOVA). 
We will report whether sensitivity analyses result in deviations from the pattern of significance to 
the main analyses (i.e., any significant differences between conditions becoming not significant, and 
vice versa). 

07/04/2020, pre-registered 
12 
ED and SEP Online Supermarket Study 
7.7. Secondary analyses 
Moderated mediation analysis 
We will describe health and weight control motivation in the overall sample using mean and 
standard deviation and report the correlation (Pearson’s) between the health and weight control 
motivation scores and level of education. 
If the primary analyses suggest that level of education moderates the effect of labelling or proportion 
on the mean ED of foods purchased (i.e., the labelling*level of education or proportion*level of 
education interaction is significant), mediation analyses will be performed in order to examine the 
extent to which 1/ health food choice motive, 2/ weight control food choice motive mediates the 
effect of level of education on the mean ED. 
Conceptual diagram example (labelling): 
Statistical diagram example (labelling): 
 
 
 
Conditional indirect effect of level of education on the mean ED through a mediator (M) = a(b1+ 
b2labelling). 
The moderated mediation will be tested by estimating the conditional indirect effect of level of 
education on the mean ED through M for labelling and no labelling conditions (resp. the default and 
increased proportion conditions) and testing the conditional indirect effect for those conditions using 
bias-corrected bootstrap. We will use the PROCESS macro (Model 15) on SAS software that provides 
asymmetric bias-corrected bootstrap confidence intervals for inference about the conditional 
indirect effects using 5,000 bootstrap samples [37]. Moderated mediation will be tested by 
determining whether or not the confidence interval for the difference between conditional indirect 
effects for labelling vs. no labelling conditions (resp. the increased and baseline availability 
conditions) contains zero. 
Analyses of secondary outcomes 
For descriptive purposes we will code each participant product selection based on the food 
categories outlined in the shopping list and repeat the primary analysis strategy on each of the 10 
food categories individually. 
To further investigate the effect of the interventions and level of education, we will repeat the 
primary analysis strategy with the following dependent variables: 
- 
on total energy of the foods purchased; 
- 
on energy from total sugar; 
- 
on energy from SFA; 
- 
on salt content; 

07/04/2020, pre-registered 
13 
ED and SEP Online Supermarket Study 
- 
on proportion of lower ED foods in the basket of foods purchased; 
- 
on cost of the foods purchased. 
We will also repeat the primary analysis including the interaction between labelling and proportion 
in the model. 
Debriefing questionnaire 
We will explore whether the shopping list was valid and the extent to which participants reported 
being influenced by calorie content when making food choices. Responses to the debriefing 
questionnaire will be analysed. 
- 
We will report the distribution of responses for validity and kcal influence (mean, SD, 
median, quartiles Q1 and Q3) in the overall sample. 
- 
Two ANCOVAs will be run (as in primary analysis) to test the effect of labelling, proportion 
and level of education on (a) validity and (b) kcal influence to investigate whether the 
responses differ across conditions and SEP. 
For the labelling conditions only, we will report the percentage of participants who know what the 
“healthier choice” badge means, i.e., who tick the answer “Fewer calories per gram option”. 
7.8. Sample size 
To observe differences between the intervention groups and interaction with SEP 
In a previous study (n=1,088) using the online supermarket platform, two types of nutritional 
interventions targeting a reduction of saturated fat (SFA) were compared: 1/ altering the default 
order of products in ascending order of SFA content 2/ offering explicit swaps with lower SFA [28]. 
This study showed a large main effect (f=0.42) of altering the default order: -4.78% (95%IC: -5.43 to -
4.12) of energy from SFA; and a small-to-medium main effect (f=0.12) of offering swaps: -1.48% 
(95%IC: -2.19 to -0.76) of energy from SFA. Regarding ED reduction, this study showed a small-to-
medium main effect (f=0.14) of altering the default order: -5.16 (95%IC: -7.3 to -3.02); and no 
significant main effect (f=0.04) of offering swaps -1.5 (95% IC: -3.65 to 0.67). 
Based on these previous results, we will power our analyses to detect small main effects (f=0.1) of 
the labelling and increased proportion interventions. In an ANCOVA including four groups (control, 
labelling, increased proportion, increased proportion & labelling) and one covariate (level of 
education), to detect a main effect of labelling or increased proportion we will require a sample size 
of 788 participants (197 per group) for 80% power at α = 0.05 (GPower 3.1). 
A sample size of 788 participants will allow to detect small interaction effects (f=0.1) of labelling or 
increased proportion with level of education in an ANCOVA including four groups (control, labelling, 
increased proportion, increased proportion & labelling) and one covariate (level of education) for 
80% power at α = 0.05 (GPower 3.1). 
To observe a mediated effect of SEP through health and weight control motives 
Based on existing literature we hypothesise that the relationship between SEP and food choice 
motives will be small-to-medium in size [38]. Moreover, in a previous trial we ran using a virtual fast 
food restaurant (osf.io/ajcr6), we found a small-to-medium correlation between level of education 
and healthiness motivation (r=0.17) as well as small-to-medium correlation between healthiness 
motivation and kcal ordered (r=-0.25). Empirical estimates of sample sizes needed for 0.8 power in 
mediation analyses indicate that samples of ≈ 380 are sufficient to detect mediation through 
pathways that are small and small-to-moderate in statistical size using bias-corrected bootstrap tests 

07/04/2020, pre-registered 
14 
ED and SEP Online Supermarket Study 
[39]. Thus, a sample of 788 participants (i.e., 394 per labelling or proportion condition) allow for 
adequate power in our planned moderated mediation analysis. 
We will recruit a sample of 1,000 participants (= participants who completed the entire study) to 
account for potential data loss due to incorrect answers, technical problems, failed attention checks, 
no compliance with the shopping task (up to ~20%) resulting in a minimum sample of 788 
participants for our primary analyses. 
 

07/04/2020, pre-registered 
15 
ED and SEP Online Supermarket Study 
REFERENCES 
 
[1] 
World Health Organization, “Obesity and Inequities,” World Heal. Organ., p. 48, 2014. 
[2] 
P. Monsivais and A. Drewnowski, “Lower-energy-density diets are associated with higher 
monetary costs per kilocalorie and are consumed by women of higher socioeconomic status,” 
J Am Diet Assoc, vol. 109, pp. 814–22, May 2009. 
[3] 
A. Aggarwal, P. Monsivais, A. J. Cook, and A. Drewnowski, “Does diet cost mediate the 
relation between socioeconomic position and diet quality?,” Eur. J. Clin. Nutr., vol. 65, no. 9, 
pp. 1059–66, Sep. 2011. 
[4] 
J. P. Karl and S. B. Roberts, “Energy Density, Energy Intake, and Body Weight Regulation in 
Adults,” Adv. Nutr., vol. 5, no. 6, pp. 835–850, 2014. 
[5] 
A. Drewnowski and S. Specter, “Poverty and obesity: the role of energy density and energy 
costs,” Am. J. Clin. Nutr., vol. 79, no. 1, pp. 6–16, 2004. 
[6] 
L. Goffe, S. Rushton, M. White, A. Adamson, and J. Adams, “Relationship between mean daily 
energy intake and frequency of consumption of out-of-home meals in the UK National Diet 
and Nutrition Survey,” Int. J. Behav. Nutr. Phys. Act., vol. 14, no. 1, pp. 1–11, 2017. 
[7] 
Office for National Statistics, “Family spending in the UK: April 2017 to March 2018,” 2019. 
[8] 
S. Capewell and A. Capewell, “An effectiveness hierarchy of preventive interventions: 
Neglected paradigm or self-evident truth?,” J. Public Heal. (United Kingdom), vol. 40, no. 2, 
pp. 350–358, 2017. 
[9] 
T. R. Frieden, “A framework for public health action: The health impact pyramid,” Am. J. 
Public Health, vol. 100, no. 4, pp. 590–595, 2010. 
[10] 
E. M. VanEpps, C. A. Roberto, S. Park, C. D. Economos, and S. N. Bleich, “Restaurant Menu 
Labeling Policy: Review of Evidence and Controversies,” Curr. Obes. Rep., vol. 5, no. 1, pp. 72–
80, 2016. 
[11] 
D. Sarink, A. Peeters, R. Freak-Poli, A. Beauchamp, J. Woods, K. Ball, and K. Backholer, “The 
impact of menu energy labelling across socioeconomic groups: A systematic review,” 
Appetite, vol. 99, pp. 59–75, 2016. 
[12] 
A. Beauchamp, K. Backholer, D. Magliano, and A. Peeters, “The effect of obesity prevention 
interventions according to socioeconomic position: A systematic review,” Obes. Rev., vol. 15, 
no. 7, pp. 541–554, 2014. 
[13] 
R. A. Crockett, S. E. King, T. M. Marteau, A. T. Prevost, G. Bignardi, N. W. Roberts, B. Stubbs, 
G. J. Hollands, and S. A. Jebb, “Nutritional labelling for healthier food or non-alcoholic drink 
purchasing and consumption,” Cochrane Database Syst. Rev., vol. 2, p. CD009315, 2018. 
[14] 
J. Adams, O. Mytton, M. White, and P. Monsivais, “Why Are Some Population Interventions 
for Diet and Obesity More Equitable and Effective Than Others? The Role of Individual 
Agency,” PLoS Med., vol. 13, no. 4, pp. 1–7, 2016. 
[15] 
K. Backholer, A. Beauchamp, K. Ball, G. Turrell, J. Martin, J. Woods, and A. Peeters, “A 
framework for evaluating the impact of obesity prevention strategies on socioeconomic 
inequalities in weight,” Am. J. Public Health, vol. 104, no. 10, pp. e43–e50, 2014. 
[16] 
L. Dubé and I. Cantin, “Promoting health or promoting pleasure? A contingency approach to 
the effect of informational and emotional appeals on food liking and consumption.,” 

07/04/2020, pre-registered 
16 
ED and SEP Online Supermarket Study 
Appetite, vol. 35, no. 3, pp. 251–62, Dec. 2000. 
[17] 
G. V. Pepper and D. Nettle, “The behavioural constellation of deprivation: causes and 
consequences,” Behav. Brain Sci., no. 2017, pp. 1–72, 2017. 
[18] 
S. E. Forwood, A. L. Ahern, T. M. Marteau, and S. A. Jebb, “Offering within-category food 
swaps to reduce energy density of food purchases: A study using an experimental online 
supermarket,” Int. J. Behav. Nutr. Phys. Act., vol. 12, no. 1, pp. 1–10, 2015. 
[19] 
HESA, “Higher Education Student Statistics: UK, 2017/18,” Statistical Bulletin, SB252, 2019. 
[Online]. Available: https://www.hesa.ac.uk/news/17-01-2019/sb252-higher-education-
student-statistics. [Accessed: 11-Jun-2019]. 
[20] 
Office for National Statistics, “2011 Census-based reweighting of Labour Force Survey 
estimates,” 2014. 
[21] 
L. Johnson, D. C. Wilks, A. K. Lindroos, and S. A. Jebb, “Reflections from a systematic review of 
dietary energy density and weight gain: Is the inclusion of drinks valid?,” Obes. Rev., vol. 10, 
no. 6, pp. 681–692, 2009. 
[22] 
Public Health England and Food Standards Agency, “National Diet and Nutrition Survey: 
Results from Years 7 and 8 (combined) of the Rolling Programme (2014/2015 to 
2015/2016).,” PHE publications. p. Table 6.1, 2018. 
[23] 
I. Ikonen, F. Sotgiu, A. Aydinli, and P. W. J. Verlegh, “Consumer effects of front-of-package 
nutrition labeling: an interdisciplinary meta-analysis,” J. Acad. Mark. Sci., 2019. 
[24] 
Office for National Statistics, “Chapter 3: Equivalised income,” in Compendium: Family 
Spending in the UK, 2015. 
[25] 
A. T. Smith, M. Noble, S. Noble, G. Wright, and D. Mclennan, “The English Indices of 
Deprivation 2015: Research report,” London, 2015. 
[26] 
N. E. Adler, E. Epel, G. Casterllazzo, and J. Ickovics, “Relationship of subjective and objective 
social status with psychological and physical health in healthy white women,” Heal. Psychol., 
vol. 19, no. 6, pp. 586–592, 2000. 
[27] 
A. Steptoe, T. M. Pollard, and J. Wardle, “Development of a Measure of the Motives 
Underlying the Selection of Food: the ‘Food Choice Questionnaire,’” Appetite, vol. 25, pp. 
267–284, 1995. 
[28] 
D. A. Koutoukidis, S. A. Jebb, J. M. Ordóñez-mena, M. Noreik, M. Tsiountsioura, S. Kennedy, S. 
Payne-riches, P. Aveyard, J. Ordonez-mena, M. Noreik, M. Tsiountsioura, S. Kennedy, S. P. 
Riches, P. Aveyard, and C. Piernas, “Effectiveness of interventions to reduce the saturated fat 
content of food purchases: a factorial randomised controlled trial in an experimental online 
supermarket,” IJBNPA, pp. 1–14, 2019. 
[29] 
S. Payne Riches, P. Aveyard, C. Piernas, M. Rayner, and S. A. Jebb, “Optimising swaps to 
reduce the salt content of food purchases in a virtual online supermarket: A randomised 
controlled trial,” Appetite, vol. 133, no. November 2018, pp. 378–386, 2019. 
[30] 
Y. Miller, “Recommendations for the truncation of Body Mass Index in population data,” NSW 
Centre for Physical Activity and Health, no. September. pp. 1–16, 2003. 
[31] 
R. Hardy, J. Johnson, and A. Park, “Harmonised height, weight and BMI user guide,” no. July. 
Closer. Cohort & Longitudinal Studies Enhancement Resources, pp. 1–17, 2016. 
[32] 
G. Cowburn and L. Stockley, “Consumer understanding and use of nutrition labelling: a 

07/04/2020, pre-registered 
17 
ED and SEP Online Supermarket Study 
systematic review,” Public Health Nutr., vol. 8, no. 01, 2008. 
[33] 
A. Breck, J. Cantor, O. Martinez, and B. Elbel, “Who reports noticing and using calorie 
information posted on fast food restaurant menus?,” Appetite, vol. 81, pp. 30–36, 2014. 
[34] 
S. A. Spiller, G. J. Fitzsimons, J. G. Lynch, and G. H. Mcclelland, “Spotlights, Floodlights, and 
the Magic Number Zero: Simple Effects Tests in Moderated Regression,” J. Mark. Res., vol. 50, 
no. 2, pp. 277–288, 2013. 
[35] 
P. O. Johnson and J. Neyman, “Tests of Certain Linear Hypotheses and Their Application to 
Some Educational Problems,” Stat. Res. Mem., vol. 1, pp. 57–93, 1936. 
[36] 
A. F. Hayes and J. Matthes, “Computational procedures for probing interactions in OLS and 
logistic regression: SPSS and SAS implementations,” Behav. Res. Methods, vol. 41, no. 3, pp. 
924–936, 2009. 
[37] 
A. F. Hayes, “PROCESS: A Versatile Computational Tool for Observed Variable Mediation, 
Moderation, and Conditional Process Modeling,” White Paper, 2012. [Online]. Available: 
http://www.afhayes.com/ public/process2012.pdf. 
[38] 
R. Pechey, P. Monsivais, Y. L. Ng, and T. M. Marteau, “Why don’t poor men eat fruit? 
Socioeconomic differences in motivations for fruit consumption,” Appetite, vol. 84, pp. 271–
279, 2015. 
[39] 
M. S. Fritz and D. P. Mackinnon, “Required Sample Size to Detect the Mediated Effect,” 
Psychol. Sci., vol. 18, no. 3, pp. 233–239, 2007. 
 
 

07/04/2020, pre-registered 
18 
ED and SEP Online Supermarket Study 
APPENDIX A: AUDIENCE (PROLIFIC WEBSITE) 
1. Age 
o 18 years old or over 
 
2. Current country of residence 
o UK 
 
3. Fluent language 
o English 
 
4. Diet restriction 
o None 
 
5. Gender 
50% of participants 
o Male 
50% of participants 
o Female 
 
6. Students 
96.5% of participants 
o No 
3.5% of participants 
o Yes 
 
7. Highest education level 
60% of participants 
o No formal qualifications 
o Secondary education (e.g. GED/GCSE) 
o High school diploma/A-levels 
40% of participants 
o Technical/community college 
o Undergraduate degree (BA, BS, other) 
o Graduate degree (MA, MSc, MPhil, other) 
o Doctoral degree (PhD, MD, other) 
 
8. Are you the main (or shared) grocery shopper for the food that your household eats? 
o Yes 
 
 

07/04/2020, pre-registered 
19 
ED and SEP Online Supermarket Study 
APPENDIX B: RECRUITMENT TEXT 
“This is a study examining food purchases when shopping online. You will do some online grocery 
shopping on an experimental supermarket website and fill some questionnaires in about yourself. 
Please read the instructions carefully and answer the questions as accurately as possible. Failure to 
comply with the instructions may result in your submission being rejected. Please click on the start 
button to proceed. Overall the study will take no more than 25 minutes.” 
 
 

07/04/2020, pre-registered 
20 
ED and SEP Online Supermarket Study 
APPENDIX C: INFORMATION PAGE 
 
Online Supermarket Study 
 
You are being 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 how different people make food 
purchases when shopping online. 
  
Why have I been chosen to take part? 
 
We are recruiting volunteers who fulfil the following criteria: 
1. Aged 18 years 
2. Fluent English speaker 
3. Reside in the UK 
4. Do not have any dietary restriction 
5. Are the main (or shared) grocery shopper for their household 
 
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 provide some information about yourself (e.g., age, gender), before then 
completing an online grocery shopping task. You will also fill some 
questionnaires in about yourself. 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 study will take no 
more than 25 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 or the 

07/04/2020, pre-registered 
21 
ED and SEP Online Supermarket Study 
principal investigator (see contact details below). 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. 
 
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 
How will my data be collected? 
Through an online questionnaire. 
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).  

07/04/2020, pre-registered 
22 
ED and SEP Online Supermarket Study 
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 Dr Lucile Marty (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 principle investigator:  
Dr Lucile Marty 
2.41b, Eleanor Rathbone Building 
Bedford Street South 
University of Liverpool, 
Liverpool,  
L69 7ZA, 
UK 
email: lucile.marty@liverpool.ac.uk 
 
or the data protection officer: 
Victoria Heath 
The Foundation Building, 
765 Brownlow Hill, 
University of Liverpool, 
Liverpool, 
L69 7ZX, 
UK, 
email: V.Heath@liverpool.ac.uk  
 
I confirm I have read the information sheet 
 
o Yes 
 
 

07/04/2020, pre-registered 
23 
ED and SEP Online Supermarket Study 
APPENDIX D: CONSENT PAGE 
 
Online Supermarket Study 
 
I confirm that I have read and have 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 any 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 data protection requirements at the University of 
Liverpool. In addition, I understand that personal information collected about me 
that can identify me (e.g. postcode) will never be shared beyond the study team. 
 
I understand that shortly after completing the study, researchers will keep my 
personal data (e.g. postcode) 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 other research in the future. 
 
I understand that I can ask for access to any of the information I provide and I can request the 
destruction or alteration of that information if I wish for up to 28 days after participating in 
the study. I understand that following this I will no longer be able to request access to or 
withdrawal of the information I provide because this information will have been deleted. 
 
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. 

07/04/2020, pre-registered 
24 
ED and SEP Online Supermarket Study 
I agree and consent to take part in the above study 
 
o Yes 
 
 

07/04/2020, pre-registered 
25 
ED and SEP Online Supermarket Study 
APPENDIX E: BASELINE QUESTIONNAIRE 
Eligibility screening: 
- 
Are you a fluent English speaker? 
o Yes 
o No ➔ screened out 
 
- 
Do you currently reside in the UK? 
o Yes 
o No ➔ screened out 
 
- 
Do you have any dietary restrictions? 
o Vegetarian ➔ screened out 
o Vegan ➔ screened out 
o Gluten-free ➔ screened out 
o Sugar-free ➔ screened out 
o Diary/lactose-free ➔ screened out 
o Food allergy (e.g. milk, eggs, nut, wheat, fish, etc.) ➔ screened out 
o None 
o Other ➔ screened out 
 
- 
Are you the main (or shared) grocery shopper for the food that your household eats? 
o Yes 
o No ➔ screened out 
Questionnaire: 
1. Gender 
o Male 
o Female 
o Other 
 
2. Age 
o _ _ (free text; range of 18-99) 
 
3. Ethnicity 
o White 
o Black 
o Asian 
o Mixed 
o Other 
 
4. What is your current employment status? 
o Full or part-time 
o Student 
o Retired 
o Temporary or permanently sick or disabled 
o Looking after home/family 
o Other unemployed 

07/04/2020, pre-registered 
26 
ED and SEP Online Supermarket Study 
 
5. What is your highest educational qualification? If you are a student please select the 
diploma being studied for. 
o No formal qualifications 
o 1–3 GCSEs or equivalent 
o 4+ GCSEs or equivalent 
o A level or equivalent 
o Certificate of higher education (CertHE) or equivalent 
o Diploma of higher education (DipHE) or equivalent 
o Bachelor or equivalent 
o Master’s degree or equivalent 
o Doctorate or equivalent 
 
6. After leaving school (i.e. at 16 years old), how many further years of higher education (i.e. a 
formal course) did you study for? 
Examples: 
If you left school and did not go on to study further in higher education, your answer would be 0. 
If you left school and then studied for two years for A levels, your answer would be 2. 
If you completed A levels over two years and then also studied for a three year undergraduate degree, 
your answer would be 5. 
_ _ (free text) 
 
7. What is your annual after tax household income, including all earners in your household, in 
GBP (to the nearest £1000)? 
£_ _ _ _ _ _ (free text; range 0-999,999) 
 
8. How many people live at your house, including you? 
_ _ adult(s) or child(ren) aged 14 and over (free text; range of 1-20) 
_ _ child(ren) aged under 14 (free text; range of 1-20) 
 
9. What is the postcode of your current home address? 
_ _ _ _ _ _ (free text) 
 
10. This is an attention check. How many times have you visited the planet Mars? 
o Several times 
o Just once 
o Never 
 
11. 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?  

07/04/2020, pre-registered 
27 
ED and SEP Online Supermarket Study 
 
Choose the number whose position best represents where you would be on this ladder: 
_ _ (free text: range 1-10) 
 
12. On average, how much do you spend on supermarket shopping per week? 
£_ _ _ 
 
13. How often, on average over the past year, have you shopped in a supermarket for food or 
groceries? 
o Less than once a month 
o 1-3 times per month 
o 1-2 times per week 
o 3-4 times per week 
o 5 times per week or more often 
 
14. How often, on average over the past year, have you shopped online for food or groceries? 
o Never or not in the last year 
o 1-3 times in the last year 
o 4-11 times in the last year 
o 1-3 times per month 
o once per week or more often 
 
15. Are you currently dieting? 
o Yes 
o No 
 
16. Weight 
_ _ . _ kg 

07/04/2020, pre-registered 
28 
ED and SEP Online Supermarket Study 
_ _ st and _ _ lb 
 
17. Height 
_ _ _ cm 
_ ft and _ _ in 
 
 
 

07/04/2020, pre-registered 
29 
ED and SEP Online Supermarket Study 
APPENDIX F: ONLINE SHOPPING TASK INSTRUCTION 
“We would like you to do online grocery shopping on a supermarket website. This is not a real 
commercial site, and you will not be asked to spend your own money. 
You are given a shopping list and we ask you to buy all the items on the list. You can cross out the 
items on the list once you have added them to your trolley. You do not need to buy additional items. 
To search for the items from the shopping list, you can either go through the website categories or 
use the searching bar by copy-pasting the name of the shopping list item. 
When doing the shopping task, please select foods you and your household would be likely to 
choose.” 
 
 

07/04/2020, pre-registered 
30 
ED and SEP Online Supermarket Study 
APPENDIX G: HEALTH AND WEIGHT CONTROL MOTIVES 
Instruction: “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… 
 
 
Not at all 
important 
1 
A little 
important 
2 
Moderately 
important 
3 
Very 
important 
4 
Health 
1. 
contains a lot of vitamins and 
minerals 
o 
 
o 
 
o 
 
o 
 
2. 
keeps me healthy 
o 
 
o 
 
o 
 
o 
 
3. 
is nutritious 
o 
 
o 
 
o 
 
o 
 
4. 
is high in protein 
o 
 
o 
 
o 
 
o 
 
5. 
is good for my 
skin/teeth/hair/nails etc. 
o 
 
o 
 
o 
 
o 
 
6. 
is high in fibre and roughage 
o 
 
o 
 
o 
 
o 
 
Weight control 
7. 
is low in calories 
o 
 
o 
 
o 
 
o 
 
8. 
helps me control my weight 
o 
 
o 
 
o 
 
o 
 
9. 
is low in fat 
o 
 
o 
 
o 
 
o 
 
 
 
 

07/04/2020, pre-registered 
31 
ED and SEP Online Supermarket Study 
APPENDIX H: DEBRIEFING QUESTIONNAIRE 
Aim guessing: 
What do you think we were expecting to find in this study? 
[Free text] 
Questionnaire: 
- 
What do you think this logo means? 
Select which of the following apply to the logo. 
□ Lower in price option 
□ Fewer calories per gram option 
□ Lower in salt per gram option 
□ Lower in sugar per gram option 
□ Lower in saturated fat per gram option 
 
- 
The choices I made during online shopping were influenced by how many calories I thought 
were in the options available. 
 
o  
o  
o  
o  
o  
o  
o  
1 
Strongly 
disagree 
2 
Disagree 
3 
Slightly 
disagree 
4 
Neither 
agree nor 
disagree 
5 
Slightly 
agree 
6 
Agree 
7 
Strongly 
agree 
 
- 
I would normally buy [the 10 items on the shopping list]: 
 
 
Never 
1 
Very 
Rarely 
2 
Rarely 
3 
Occasionally 
4 
Frequently 
5 
Very 
Frequently 
6 
Item 1 
o  
o  
o  
o  
o  
o  
Item 2 
o  
o  
o  
o  
o  
o  
Item 3 
o  
o  
o  
o  
o  
o  
Item 4 
o  
o  
o  
o  
o  
o  
Item 5 
o  
o  
o  
o  
o  
o  
Item 6 
o  
o  
o  
o  
o  
o  
Item 7 
o  
o  
o  
o  
o  
o  
Item 8 
o  
o  
o  
o  
o  
o  
Item 9 
o  
o  
o  
o  
o  
o  
Item 10 
o  
o  
o  
o  
o  
o  
 
- 
What is your highest educational qualification? If you are a student please select the 
diploma being studied for. *Consistency check* 
o No formal qualifications 

07/04/2020, pre-registered 
32 
ED and SEP Online Supermarket Study 
o 1–3 GCSEs or equivalent 
o 4+ GCSEs or equivalent 
o A level or equivalent 
o Certificate of higher education (CertHE) or equivalent 
o Diploma of higher education (DipHE) or equivalent 
o Bachelor or equivalent 
o Master’s degree or equivalent 
o Doctorate or equivalent 
 

07/04/2020, pre-registered 
33 
ED and SEP Online Supermarket Study 
APPENDIX I: DEBRIEFING TEXT 
“In this study we were interested in the effect of nutrition interventions on online grocery shopping. 
You have seen one version of the online supermarket but other participants have seen different ones. 
The difference between the four versions of the online supermarket is the food items they offer. In 
the first version, the food offer reflects what you can find in an online supermarket in the UK; in the 
second one low-energy badges are added to indicate the options with fewer calories per gram within 
a food category.; in the third one the proportion of lower-energy food items is increased; in the 
fourth one low-energy badges are added and the proportion of lower-energy food items is increased. 
We will compare the energy per 100g of the foods purchased by the participants from the four 
versions of the online supermarket. The results will help to identify the most promising intervention 
to reduce the overall energy of our diets.” 
“Thank you very much for your participation in our study!”