Appendix B - Methodology NI Report NDNS 2019-2023
Source: data.gov.uk (2025-10-10)

National Diet and Nutrition Survey 2017 to 2023 Report for Northern Ireland. This report presents results from 2017-2023 of the National Diet and Nutrition Survey (NDNS) for Northern Ireland. NDNS is a continuous cross-sectional survey, designed to assess the diet, nutrient intake and nutritional status of the general population aged 18 months and over living in private households in the UK.

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
Appendix B:  
Methodology for National Diet and 
Nutrition Survey 2019 to 2023 
 
B.1 Overview of methodology  
This appendix provides an overview of the methodology for years 12 to 15 of the 
National Diet and Nutrition Survey (NDNS). Interviewing for these fieldwork years 
was carried out between October 2019 and July 2023. 
The NDNS has run continuously since 2008 and is a cross-sectional survey, 
designed to be representative of the UK population. As with all government surveys, 
the NDNS was impacted by the COVID-19 global pandemic, and from March 2020 
the survey methodology and protocols had to be adapted in line with government 
advice and regulations. Further detail is provided in section B.1.2. 
Field documents for fieldwork year 15 are provided in the appendices; earlier 
versions (fieldwork years 12 to 14) are available on request. Diary-related 
documents and protocols used prior to year 12 can be found in the years 9 to 11 
report.   
B.1.1 Methodological changes introduced from Year 12 
Dietary data collection 
For years 1 to 11 (2008 to 2019) of the NDNS, dietary data was collected over 4 
consecutive days using a paper food diary with estimated portion weights. In 2018 
the consortium, in conjunction with Public Health England1 and the UK Food 
Standards Agency (FSA), undertook a review to appraise whether this method 
continued to remain optimal from both a scientific and financial point of view. As a 
result, the introduction of an online dietary assessment tool was proposed to provide 
an automated data collection method, compatible with new technologies and with 
potential to improve data quality and reduce costs. A further review of available tools 
resulted in the selection of Intake24 which was introduced from year 12 (2019) to 
replace the paper diary. There was a gap in fieldwork between the end of year 11 
(May 2019) and the start of year 12 (October 2019) to allow for implementation of the 
method change. Table B.4 at the end of this chapter provides an overview of 
methodological changes in years 12 to 15 and appendix A provides full details of the 
dietary data collection and change of methods. 
 
1 From 1 October 2021, responsibility for the NDNS contract transferred from Public Health England 
to the Office for Health Improvement and Disparities (OHID). 

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
Participant selection 
From year 12 a more cost-efficient model for the selection of participants within a 
household was introduced. The aim remained to achieve a representative sample of 
500 adults (aged 19 years and over) and 500 children (aged 18 months to 18 years) 
from the core UK sample. To achieve these numbers in years 1 to 11, one adult and 
one child were selected in around one-third of addresses and one child (no adult) in 
around two-thirds of addresses. From year 12, the protocol was amended so that up 
to 2 adults and one child were selected from around one-third of addresses (referred 
to as ‘basic addresses’) and up to 2 children (no adults) were selected from the 
remaining two-thirds of addresses (referred to as ‘young person addresses’). More 
detail on the issued sample sizes and participant selection is provided in section B.2.  
 
B.1.2 Methodological changes as a result of the COVID-19 
pandemic 
 
Fieldwork was suspended on 18 March 2020 following UK government advice to 
avoid non-essential travel and contact with others due to the COVID-19 outbreak. On 
23 March 2020 the government issued a ‘stay at home’ instruction and the first 
national UK lockdown began. The suspension was initially agreed for a 2-month 
period but was eventually extended until October 2020.  
When stage one (interviewer) fieldwork recommenced in October 2020, it was with 
year 13 fieldwork (year 12 did not recommence) and a ‘knock-to-nudge’ methodology 
whereby an interviewer visited an address (but, in order to limit contact, did not enter 
the property). The interviewer provided information about the survey, completed 
required participant selections and arranged to complete the interview remotely, over 
the telephone. This approach was used throughout year 13 and for the first 5 months 
of year 14 fieldwork (April to August 2021). Face-to-face interviewing resumed in 
September 2021, although the option of a remote (telephone) interview was retained 
for participants who did not wish to have a face-to-face visit for the remainder of year 
14 fieldwork and throughout year 15 fieldwork which commenced in April 2022. 
Table B4 summarises how methods changed in each fieldwork year in order to 
accommodate the restrictions of the pandemic.  
B.2 Sample design  
The aim of the NDNS is to achieve a representative sample of 500 adults (aged 19 
years and over) and 500 children (aged 18 months to 18 years). As described in 
section B.1.1, the participant selection method was adjusted from year 12 onwards 
to provide a more cost-efficient sample design. Further changes to the sample 
design were then necessary from year 13 onwards to compensate for lower 
achieved response rates due to the COVID-19 pandemic. 
B.2.1 Selecting addresses  

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
A sample for each year was drawn from the PAF. Table B.1 summarises the number 
of PSUs and addresses selected for the core, reserve and shortfall samples.  
The core sample was the main, issued sample; the reserve sample refers to the 
PSUs (addresses) which would be issued in full or in part should the number of 
achieved (productive) cases and expected response rate fall below target in a given 
fieldwork year. The shortfall sample refers to a further set of PSUs and addresses 
which were drawn in year 14 to make up the shortfall due to the additional impact of 
COVID-19. This ‘shortfall sample’ was issued in England, Scotland and Wales 
between January and March 2022. 
Table B.1: Summary of selected addresses 
Sample type 
Year 12a 
Year 13 
Year 14 
Year 15 
Core UK 
sample 
3,335 
addresses 
from 115 
PSUs 
3,335 
addresses 
from 115 
PSUs 
3,335 
addresses 
from 115 
PSUs 
3,795 
addresses 
from 115 
PSUs 
Reserve 
sample 
522 
addresses in 
18 PSUs 
522 
addresses in 
18 PSUs 
522 
addresses in 
18 PSUs 
660 
addresses in 
20 PSUs 
Shortfall 
sample 
Not applicable 
Not applicable 
3,800 
addresses 
from 95 PSUs 
Not applicable 
Number of 
addresses per 
PSU 
29 (8 basic, 
21 young 
person) 
29 (8 basic, 
21 young 
person) 
29 (8 basic, 
21 young 
person) 
 
40 (11 basic, 
29 young 
person) in 
shortfall 
sample 
 33 (12 basic, 
21 young 
person) 
a Year 12 fieldwork was suspended in March 2020 due to the COVID-19 pandemic; a total of 2,553 
addresses were issued to interviewers prior to the suspension. 
 
At each address, the interviewer established the number of households and, in 
cases where there were 2 or more, selected one household at random.  
B.2.1 Selecting participants  
As only around one-third of households contain children2, over-sampling of children 
was required to achieve, as far as possible, equal numbers of adult (19 years and 
over) and child (18 months to 18 years) participants in each fieldwork year. Selected 
addresses in each PSU were randomly allocated to one of 2 address types: a ‘basic’ 
or a ‘young person’ address. At ‘basic’ addresses interviewers randomly selected up 
to 2 adults (aged 19 years or over) and one child (aged 18 months to 18 years) and 
at ‘young person’ addresses, the interviewer conducted a doorstep screen to identify 
addresses with children and then selected up to 2 children, each from a different 
 
2 Families and households in the UK - Office for National Statistics (ons.gov.uk) 

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
NDNS age group (18 months to 3 years, 4 to 10 years, 11 to 18 years) for interview. 
The number of addresses allocated to each address type in years 12 to 15 is shown 
in table B.1. 
Further details about the sample design are provided in appendix BB. 
 
B.3 Ethics approval  
Ethics approval for the study was obtained from the Cambridge South NRES 
Committee (Ref. No. 13/EE/0016).  
 
B.4 Fieldwork  
Fieldwork was carried out by NatCen’s panel of interviewers and biomedical 
fieldworkers. In Northern Ireland, stage 1 fieldwork for the core sample was carried 
out by interviewers working for the Northern Ireland Statistics and Research Agency 
(NISRA).  
For year 12, stage 1 (interviewer) fieldwork commenced on the first weekday of the 
month, and interviewers were given 6 weeks in which to complete their assignment. 
Stage 2 (biomedical fieldworker) fieldwork for a particular month started 8 weeks 
after the interviewer deadline. Biomedical fieldworkers had up to 7 weeks to 
complete their work. 
Following the COVID-19 pandemic and subsequent resumption of stage one in 
October 2020, fieldwork was conducted under a more flexible approach. Fieldwork 
points were allocated and worked as close as possible to their original issue date, 
with interviewers covering as much of a point as possible during the 6-week 
fieldwork period, however extensions were granted to help with fieldworker 
availability, coverage and response. 
Biomedical fieldwork did not recommence until October 2021 as it was not possible 
for this stage, in particular blood sampling, to be conducted remotely. This meant 
that for many years 13 and year 14 participants the gap between stage one and 2 
was much longer than in other fieldwork years (between one and 22 months and an 
average of 8 months). Letters were sent to participants who had agreed to a 
biomedical fieldworker visit, to remind them of the study before biomedical 
fieldworkers made contact. In year 15 (2022 to 2023) the impact of COVID-19 had 
further receded, and there was, on average, a much shorter gap (between one week 
and 11 months and an average of 3 months) between the stage one and stage 2 
visits though the gap was still wider than in pre-pandemic fieldwork years. The 
disruption to fieldwork caused by the pandemic affected the seasonal distribution of 
collected data; the impact is discussed where relevant in the main report.  
Table B.2 shows fieldwork dates for each of the fieldwork years and stages. 
Table B.2 Fieldwork dates  

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
Fieldwork 
stage 
Year 12 
Year 13 
Year 14 
Year 15 
Stage 1 
(Interviewer)  
October 2019 
to March 
2020a 
October 2020 
to November 
2022 
April 2021 to 
November 
2022 
April 2022 to 
April 2023 
Stage 2 
(Biomedical 
fieldworker) 
November 
2019 to March 
2020b 
October 2021 
to December 
2022 
November 
2021 to April 
2023 
June 2022 to 
July 2023 
a No fieldwork was carried out from March to October 2020 due to the COVID-19 pandemic. 
b No biomedical fieldwork was carried out from March 2020 to November 2021 due to the COVID-19 
pandemic. 
 
B.5 Overview of survey components and fieldwork 
procedures  
The survey was delivered in 2 stages:  
Stage one: Interviewer  
• 4 online dietary recalls (non-consecutive days) 
• detailed background interview  
• interview with MFP  
• introduction to physical activity questionnaire (PAQ)  
• height and weight measurements (face-to-face visits only) or self-reported 
(telephone interviews) 
• collection of spot urine sample (face-to-face visits only) 
• doubly labelled water (DLW) sub study (years 12 to 14; see appendix X) 
• placement of physical activity monitor (year 15 only) 
In year 12, online PAQs were completed by participants during the visit. From 
October 2020 (year 13) participants completed the questionnaire later, via a link sent 
in a text or email after their fourth recall. From April 2021 (beginning of year 14) 
participants could access the questionnaire after their third (or their fourth) recall. 
 
Year 15 participants were asked whether they were willing to wear a physical activity 
- Axivity - monitor (PAM) for 7 days and nights. At the end of the wear period, 
participants returned the PAM by post. Accelerometry data is not presented in this 
report but will be made available via the UK Data Service.  
 
Stage 2: Biomedical fieldworker  
• blood sample  
• physical measurements, waist and hip, demispan and infant length  
• collection of information about prescribed medicines  
• placement of spot urine home collection kit (where interviewer visit was 
remote) 

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
B.5.1 Stage 1: the interviewer visits  
As outlined in B.1.2, stage 1 (interviewer) fieldwork for year 12 was carried out face-
to-face. For years 13 to 15, fieldwork operated with a mixed-mode approach: face-to-
face and remote (telephone) methods. The differences between the 2 modes are 
summarised in table B.3. 
Advance letters 
A letter and leaflet describing the purpose of the survey was sent to all sampled 
addresses before the fieldwork start date. A few days later, unless the household 
had contacted NatCen to state that they did not to take part, interviewers visited the 
addresses to determine whether each was ‘eligible’ (that is private, residential and 
occupied). At eligible addresses, they then carried out the selection process and, for 
children aged under 16 years, sought both the child’s and their parent’s (or 
guardian’s) consent to interview. 
 
Main interview 
Where stage one was carried out face-to-face, interviewers were usually able to 
carry out a single visit to a household to interview all participants who had agreed to 
take part. Further visits were carried out as necessary, for example to interview 
participants who could not be present at the main visit or to carry out additional 
elements or provide assistance with the dietary recalls.  
 Further details about information collected during the interviewer stage (and the 
fieldwork documents used) can be found in appendices C to F. The fieldwork 
documents included in the appendices are the most recent versions used during the 
fieldwork period covered by this report. Any earlier versions, for example, as adapted 
for use during the COVID-19 pandemic are available on request.  
 
Computer Assisted Personal Interview (CAPI) programme  
CAPI interviewing involves the interviewer reading questions from a laptop screen 
and entering the participants’ responses into designated fields. The CAPI 
questionnaire had 3 main elements: household composition interview, MFP interview 
and individual interview. The content of the CAPI questionnaires is shown in 
appendix D.  
Collection of dietary data: Intake24  
At the end of the CAPI questionnaire all participants were invited to complete the first 
of 4 dietary recalls using Intake24 via an embedded individual link. Intake24 is an 
online 24-hour dietary recall tool based on multiple-pass dietary assessment 
methodology (Bradley and others 2016; Foster and others 2019). The method 
involves participants providing information about everything they have eaten and 
drunk over a 24-hour period (midnight to midnight), the preceding day (called a 
dietary recall). A unique URL routed the participant directly to the Intake24 webpage 
to complete their first dietary recall. At the start of Intake24, participants were 
prompted to watch a video showing them how to use the tool. Following completion 

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
of their first dietary recall, participants were invited via email or text message, using 
contact information provided during the interview, to complete their subsequent 
dietary recalls (2, 3 and 4).  
Participants received the invite to complete their next dietary recall one to 3 days 
(randomly allocated) after completion of their previous dietary recall. Up to 3 
reminders were sent to prompt completion of the dietary recall, with a maximum 
period of 49 days over which all 4 dietary recalls could be completed. To balance the 
number of weekday and weekend dietary recalls, the Recall 3 invitation was 
scheduled to be sent on a weekend day if the previous 2 dietary recalls were 
completed on a weekday. If Recalls 1 to 3 were all completed on a weekday, the 
Recall 4 invitation was scheduled to be sent on a weekend day. Dietary recall 
invitations were sent in the morning at 7:30am asking for a recall of the previous day. 
If the requested dietary recall was not completed by late afternoon, a reminder was 
sent on the same day. Further reminders were sent on the day after the initial 
invitation and 4 days after the initial invitation if the requested dietary recall was still 
not completed. 
 
Participants who did not have internet access, or who did not feel comfortable or 
confident completing the dietary recalls independently, could request assistance for 
their dietary data collection. Assistance with completing dietary recalls was carried 
out by the MRC Epidemiology Unit team over the telephone or via Zoom video 
conferencing.  
On completion of all 4 dietary recalls, Intake24 provided participants with the option 
to view onscreen dietary feedback. The feedback provided an average daily personal 
intake for key foods and nutrients compiled from the 4 dietary recalls combined. 
Participants were also sent a thank you message via email or text. Participants 
received a £5 high street gift card as a token of appreciation for completing their first 
recall. Participants who completed 3 further recalls were sent a £20 high street gift 
card. 
Appendix A provides full details of the dietary data collection and processing 
protocols. 
Height and weight measurements  
Participants who were visited were asked if they were willing to have their height and 
weight measured by the interviewer. Participants who had a telephone interview 
were asked to self-report their height and weight.  
Protocols for height and weight measurements are provided in appendix L.  
Physical Activity questionnaires (PAQs) 
In year 12, online PAQs were completed by participants during the interviewer visit. 
Year 13 participants completed the questionnaire later, via a link sent in a text or 
email after their fourth dietary recall. In order to increase the completion rate, 

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
participants from years 14 and 15 were sent the link after their third recall and again, 
after their fourth if the PAQ had not been completed in the meantime. 
Appendix V provides full details of the physical activity questionnaires and data 
processing.   
Spot urine sample  
Participants aged 4 years and over who had a face-to-face visit were asked if they 
were willing to provide a single spot urine sample. Participants providing a spot urine 
sample received a £5 high street gift card as a token of appreciation.  Protocols and 
documents for spot urine sampling are provided in appendices C and H. The 
fieldwork documents included in the appendices are the most recent versions used 
during the fieldwork period covered by this report. Any earlier versions, for example, 
as adapted for use during the COVID-19 pandemic, are available on request.   
 
Differences between fieldwork modes 
Table B.3 outlines the differences between the face-to-face and telephone modes. 
Table B.3: Differences between fieldwork modes 
 
Face-to-face (in-home) 
Telephone (remote) 
Participant recruitment 
Advance letters sent to 
selected addresses, 
follow-up in-home visit by 
interviewer to select 
participant(s) and conduct 
interview(s) 
Advance letters sent to 
selected addresses, 
follow-up doorstep visit 
from interviewer; including 
an option to telephone 
NatCen and schedule 
interview or decline 
participation 
Participant selection 
Household and participant 
selection on doorstep 
before in-home interview 
Household and 
participant selection on 
doorstep before arranging 
telephone interview 
CAPI interview 
(background and MFP) 
In-person at participant’s 
home; could interview 
multiple participants in the 
same visit 
Remote interview 
conducted via telephone; 
separate calls for each 
participant 
Introduction of dietary 
data collection  
Explanation and first 
recall during interviewer 
visit; dates of subsequent 
recalls randomly allocated 
and invites and reminders 
sent via text or email 
Explanation during 
telephone interview, first 
recall completed following 
interview, follow-up call to 
check for issues and 
prompt completion; 
subsequent recalls 
randomly allocated and 
invites and reminders 
sent via text or email 
Dietary data collection 
assistance (if required) 
Interviewer revisited to 
assist with subsequent 
Assistance provided via 
telephone or Zoom from 

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
recalls (if, for example, 
the participant did not 
have a suitable device); 
for participants living in 
rural areas with no 
internet connection, 
assistance was provided 
via telephone from MRC 
Epidemiology Unit 
MRC Epidemiology Unit 
for participants who 
completed their CAPI 
interview remotely and 
were unable to complete 
dietary recalls without 
assistance 
Height and weight 
measurements 
Taken by interviewers 
during visit 
Self-reported  
Spot urine sample (ages 
4 years and older) 
Participant asked to 
provide spot urine sample 
during interview, which 
interviewer then posted; 
option for spot urine home 
collection kit to be left with 
participant for them to 
post back later 
Participants visited by a 
biomedical fieldworker 
and willing to provide a 
sample were left with a kit 
to take and post back the 
sample after the visit 
 
B.5.2 Stage 2: the biomedical fieldworker visit  
Stage 2 of the survey was carried out by a qualified biomedical fieldworker. All 
individuals who had completed the CAPI interview and first recall at Stage 1 were 
eligible for a biomedical fieldworker visit. This excludes 214 participants from year 12 
who agreed to have a biomedical fieldworker visit prior to fieldwork being halted in 
March 2020 but the visit did not take place as fieldwork did not resume. Biomedical 
fieldworker visits were always conducted face-to-face. 
 
At the end of stage one, interviewers provided participants with information leaflets 
and, from year 13 onwards, collected information which helped determine eligibility 
to provide a blood sample (for example, recording whether participants were taking 
anticoagulant medication). The leaflets gave details of the biomedical fieldworker 
visit (including the blood sample component) and sought agreement for the 
biomedical fieldworker to make contact. 
 
The biomedical fieldworker asked questions about prescribed medications before 
taking, with agreement or written consent as appropriate, a number of physical 
measurements and a venous blood sample.  
Measurements taken by the biomedical fieldworker  
A summary of the measurements collected during stage 2 is provided in table B.4. 
Some of the information collected by biomedical fieldworkers was limited to particular 
age groups. 
Table B.4 Summary of measurements collected during stage 2 
Measurement or procedure  
Participant  
Details of prescribed medications  
All ages  

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
Infant length measurement  
Aged 18 to 23 months  
Waist and hip circumferences  
Aged 11 years and over  
Demispan  
Aged 65 years and over and those 
aged 16 to 64 years where height 
measurement was unreliable  
Non-fasting blood sample  
Aged 18 months to 3 years and 
people not willing to fast  
Fasting blood sample  
Aged 4 years and over  
 
The biomedical fieldwork documents are provided in appendices G and H. 
Measurement protocols are provided in appendix L. The fieldwork documents 
included in the appendices are the most recent versions used during the fieldwork 
period covered by this report. Any earlier versions, for example, as adapted for use 
during the COVID-19 pandemic, are available on request.   
 
Blood sample  
Participants aged 4 years and over were asked whether they were willing to give a 
blood sample by venepuncture after an overnight fast (those aged 18 months to 3 
years were asked to provide a non-fasting blood sample).  Blood samples were 
taken by the biomedical fieldworker from participants aged 11 years and over. 
Biomedical fieldworkers qualified and experienced in paediatric phlebotomy took 
blood samples from younger children. Otherwise, blood was taken by a NatCen 
paediatric phlebotomist who accompanied the biomedical fieldworker on the visit.  
Protocols and procedures are in line with official Royal College of Nursing guidelines.  
The biomedical fieldworker obtained written consent from participants aged 16 years 
and over before the sample was taken. For children aged 18 months to 15 years, 
written consent of a parent or guardian was required and written assent from the 
child was also obtained where possible. Written agreement to store part of the blood 
sample for additional analyses at a future date was also sought.  
Participants who provided a blood sample received a £20 high street gift card as a 
token of appreciation for agreeing to this part of the study. 
B.6 Feedback to participants and GPs  
Dietary feedback 
After completing 4 dietary recalls, participants were provided with the option to 
receive detailed feedback on how their nutrient intakes compared to UK nutritional 
recommendations. The feedback was generated from Intake24 based on the 4 
recalls and also included general information on sources of healthy eating advice 
and links to websites with such advice. Further information about the dietary 
feedback can be found in appendix A and an example of the dietary feedback is 
provided in appendix J.  

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
Measurement record card 
Each participant was also offered a ‘Measurement Record Card’ on which the 
interviewer and, if appropriate, the biomedical fieldworker, recorded the person’s 
height, weight, body mass index (BMI) (if aged 16 years and over), and other age-
dependent physical measurements: waist and hip circumferences (if aged 11 years 
and over); demispan measurement (if aged 65 years and over, or measured height 
from interview was unreliable) and infant length (if aged 18 to 23 months). 
Blood analysis results 
Participants who provided a blood sample were asked whether they wished to be 
sent results of the blood sample analyses. Participants were also asked if they 
wanted details of these analyses to be sent to their GP. If an individual wished to 
receive results (and/or have them sent to their GP), written consent was obtained (or 
from the parent or guardian in the case of a child). Appendix J contains an example 
of the letters providing clinical results. 
 
B.7 Fieldwork quality control  
B.7.1 Project specific training for interviewers and biomedical fieldworkers  
All interviewers and biomedical fieldworkers working on NDNS were briefed and 
trained before undertaking an assignment and were monitored during their first 
assignment. They were also issued with comprehensive written instructions covering 
survey procedures and measurement protocols.  
B.7.2 Training for interviewers  
In year 12, all interviewers attended a one-day in person training course where they 
were fully briefed on the protocols and administration of the survey. For year 13 
onwards, interviewers who had worked on the previous survey year attended a half-
day online refresher briefing (new interviewers attended a full day).  
The full and refresher briefing sessions covered background and content, doorstep 
approach, questionnaire administration (including practice sessions) and the new 
protocols around the Intake24 dietary recall collection. All interviewers were 
accredited on taking consistent, accurate height and weight measurements, and 
those who had not worked on the survey in the preceding 12 months were re-
accredited.  
B.7.3 Training for biomedical fieldworkers  
Biomedical fieldworker in-person briefings lasted one day and covered equipment 
training, blood sampling and questionnaire administration (including practice 
sessions). Biomedical fieldworkers were also briefed on the demispan, waist and hip 
and infant length measurement protocols. All other physical measurements were 
either regularly taken by biomedical fieldworkers on NDNS and other NatCen 
surveys or the newer biomedical fieldworkers attended a general training session 
which covered these protocols.  

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
Biomedical fieldworkers who were new to NDNS biomedical fieldwork completed 3 
homework exercises (covering blood sample tube labelling, and consents and blood 
despatch) which were marked and individual feedback given prior to starting 
fieldwork. 
B.8 Weighting the survey data  
It is necessary to apply weighting factors to the data collected in NDNS for 2 
reasons: to remove any bias in the observed results which may be due to differences 
in the probability of households and individuals being selected to take part; and to 
attempt to reduce non-response bias.  
Further details about the weighting strategy are available in appendix BB. 
 
References 
Bradley J and others. Comparison of INTAKE24 (an Online 24-h Dietary Recall Tool) 
with Interviewer-Led 24-h Recall in 11-24 Year-Old Nutrients 2016: volume 8 issue 6, 
page 358.  
 
Foster E and others. Validity and reliability of an online self-report 24-h dietary recall 
method (Intake24): a doubly labelled water study and repeated-measures analysis 
Journal of Nutritional Science 30 August 2019: volume 8 e29. 
 
 
 
 
 
 

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
Table B4: Overview of methodological changes in years 12 to 15  
 
Year 12 
Year 13 
Year 14 
Year 15 
Fieldwork dates 
Interviewer: October 2019 
to March 20203 
 
Biomedical fieldworker: 
October 2019 to March 
20204 
 
 
Interviewer: October 2020 
to November 2022 
 
Biomedical fieldworker: 
November 2021 to 
December 2022 
Interviewer: April 2021 to 
November 2022 
 
Biomedical fieldworker: 
November 2021 to April 
2023 
Interviewer: April 2022 to 
April 2023 
 
Biomedical fieldworker: 
July 2022 to June 2023 
Issued sample of 
addresses 
3,335 addresses from 115 
PSUs for Core UK 
sample; 493 addresses in 
17 PSUs for NI ‘boost’; 
522 addresses in 18 
PSUs for reserve sample 
 
29 addresses per PSU  
3,335 addresses from 115 
PSUs for Core UK 
sample; 493 addresses in 
17 PSUs for NI ‘boost’; 
522 addresses in 18 
PSUs for reserve sample 
 
29 addresses per PSU  
3,335 addresses from 115 
PSUs for Core UK 
sample; 493 addresses in 
17 PSUs for NI ‘boost’; 
522 addresses in 18 
PSUs for reserve sample 
 
29 addresses per PSU,  
 
Shortfall sample of 3,800 
addresses across 95 
PSUs (GB only) with 40 
addresses per PSU 
3,795 addresses from 115 
PSUs for Core UK 
sample; 561 addresses in 
17 PSUs for NI ‘boost’; 
660 addresses in 20 
PSUs for reserve sample 
 
33 addresses per PSU 
Basic addresses 
8 addresses per PSU 
 
 
 
 
 
 
8 Basic addresses in GB 
and 9 Basic addresses in 
NI5  
 
 
 
 
8 Basic addresses in GB 
and 9 Basic addresses in 
NI 
 
Shortfall sample PSUs: 11 
Basic addresses 
 
12 Basic addresses 
 
 
 
 
 
 
 
3 This includes a 7-month period (March to October 2020) where no fieldwork was carried out due to the COVID-19 pandemic. 
4 Due to restrictions resulting from the COVID-19 pandemic, no biomedical fieldwork was carried out between  
March 2020 and November 2021. 
5 Response in Northern Ireland was higher amongst children than in Great Britain, so this split allows for more adults to be interviewed to balance the 
adult/child split. 

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
 
Selection: up to 2 adults 
and (where present) one 
child 
 
 
Selection: up to 2 adults 
and (where present) one 
child 
 
Selection: up to 2 adults 
and (where present) one 
child 
 
Selection: up to 2 adults 
and (where present) one 
child 
Young Person 
addresses 
21 YP addresses per PSU 
 
 
 
 
 
 
Selection: up to 2 children 
 
 
21 YP addresses in GB 
and 20 YP addresses in 
NI  
 
 
 
 
Selection: up to 2 children 
from different NDNS age 
groups: 1.5 to 3, 4 to 10, 
11 to18 
 
21 YP addresses in GB 
and 20 YP addresses in 
NI 
 
Shortfall sample PSUs 
had 29 YP addresses 
 
Selection: up to 2 children 
from different NDNS age 
groups: 1.5 to 3, 4 to 10, 
11 to 18 
 
 
21 YP addresses 
 
 
 
 
 
 
Selection: up to 2 children 
from different NDNS age 
groups: 1.5 to 3, 4 to 10, 
11 to 18 
 
 
Interview mode 
Face-to-face, CAPI 
 
 
 
 
 
 
 
One visit in most cases 
(additional visits for recall 
assistance if required) 
Telephone interview, 
CAPI 
 
 
 
 
 
 
2 telephone interviews 
(initial interview, recall 
follow-up) 
Flexible approach (with 
preference for face-to-
face if possible) 
 
April to August 2021: 
telephone interviews only 
(as year 13) 
 
September 2021 
onwards: face-to-face 
visits resumed (telephone 
option retained) 
 
Face-to-face visit where 
possible; telephone 
interview permitted 
 
 
Dietary assessment 
method 
Intake24 – online dietary 
recalls, for 4 randomly 
allocated days 
 
Intake24 – online dietary 
recalls, for 4 randomly 
allocated days 
 
Intake24 – online dietary 
recalls, for 4 randomly 
allocated days 
 
Intake24 – online dietary 
recalls, for 4 randomly 
allocated days 
 

National Diet and Nutrition Survey: 2019 to 2023 (years 12 to 15) 
Assistance provided by 
MRC Epidemiology Unit 
for individuals who were 
unable to complete recalls 
independently 
 
 
Assistance provided by 
MRC Epidemiology Unit 
for individuals who were 
unable to complete recalls 
independently 
Assistance provided for 
individuals who were 
unable to complete recalls 
independently (by MRC 
Epidemiology Unit, or 
interviewer re-visit) 
Assistance provided for 
individuals who were 
unable to complete recalls 
independently (by MRC 
Epidemiology Unit, or 
interviewer re-visit) 
Spot urine sample 
collection 
Participants aged 4+ 
asked by interviewer to 
provide sample 
Participants aged 4+ 
asked to provide sample 
by biomedical fieldworker 
– kit was then left for them 
to post sample back 
Face-to-face interview: 
asked by interviewer to 
provide sample (or left kit 
for participant to post 
back) 
 
Telephone interview: kit 
left by biomedical 
fieldworker 
 
Face-to-face interview: 
asked by interviewer to 
provide sample (or left kit 
for participant to post 
back) 
 
Telephone interview: kit 
left by biomedical 
fieldworker 
 
Height and weight 
measurements 
Interviewer measured 
(during visit) 
 
Self-reported  
Self-reported  
Interviewer measured or 
self-reported  
Northern Ireland 
Face-to-face as for GB 
 
All points worked remotely  All points worked remotely All points worked remotely