IP15 was used to test different methods of obtaining body measurements. First, all respondents were sent a tape measure with instructions to measure their waist and hip circumference, as well as to self-report their height and weight. Second, respondents interviewed face-to-face were asked to repeat the waist and hip measurement during the interview, with instructions from the interviewer. Third, all respondents were invited to install a mobile app on their device and use it to upload two photos of themselves. The app used the images as well as profile information entered by the respondent (age, sex, height, weight, level of activity) to calculate different body measures, including body fat percentage, visceral fat content, and waist/hip ratio.
In the initial invitation letter sent before the survey, all respondents were sent a metric-only tape measure (150cm long). The mailing included instructions and a request to do a self-measurement of their waist and hips, and a card for respondents to record their dimensions. During the interview, respondents were asked if they had completed these measures and, if so, to report what these were. If a high proportion of respondents can provide these measures reliably, this adds to the feasibility of conducting biomarker collection via the web.
The reliability of these self-reported measures was tested through the in-interview measures of waist and hips led by interviewers. The interviewers did not physically touch the respondent, but provided the tape measures, led the respondent through the measurement, and visually inspected and recorded the results. Not only did these test interviewer-collection of these measures, they also serve as “objective” measures to compare to the self-reported waist and hip measures collected elsewhere in the interview. These interviewer-led measures are also part of the validation of the BVI app data collected.
Interviewers collected height and weight measures using stadiometers and scales, which was previously done both at W2/3 and IP12. The IP12 study showed interviewers were able to collect these measures using these tools. The IP15 measurement differs slightly in regards to the scales that were used. Regular scales collecting only weight were used at IP12; at IP15, the scales also provided measures of body fat and water percent. The body fat percent is directly comparable to the BVI estimate, and the standard BMI measure (captured by height and weight) can be more broadly used in comparison to the BVI measures in regards to outcomes.
These requests for these measures were not conducted experimentally, but rather as a pilot testing feasibility and quality, and to act as validation indicators for other measures collected in the study.
These questions were asked in the questionnaire modules bodymasscapi_ip15, waistandhipcapi_ip15, selfwaistandhip_ip15, scaheightandweight_ip15.
All IP15 respondents were asked to download the app during the interview; however, it was expected that respondents would use the app after the interview or otherwise in the absence of an interviewer. A variant of the BVI app, branded and customised specifically for use in Understanding Society, was created and made available on both Android and Apple app stores.
The invitation to the app study was based on previous research done in the IP asking respondents to download and use an app. After the invitation, several follow-up questions were asked to identify if a person downloaded the app successfully or reasons why they were not participating. Those respondents for whom we had a valid email address who did not refuse to participate in the app study, were sent an email reminder after the interview, reminding them of their login credentials and where to find the app.
The experimental components of this consent request were along two dimensions: the incentive given for using the app; and how feedback was referenced. For incentives, respondents received £5 either unconditionally or conditionally based on participation. The feedback experiment had conditions of whether feedback was referenced in regards to total body fat, feedback referenced in regards to visceral body fat, or no feedback was referenced.
The controlling variables for incentives and feedback, crossed and equally allocated at the household-level, are on record o_hhsamp_ip:
ff_bvfeedback_w15 (1/3 each, allocation stratified by sampleorig ff_gridmodew15 ff_incentw15)
1 = Feedback on total body fat
2 = Feedback on visceral body fat
3 = Feedback not mentioned
ff_bvincentive_w15 (1/2 each, allocation stratified by ff_bvfeedback_w15 sampleorig ff_gridmodew15)
1 = Unconditional £5 incentive
2 = Conditional £5 incentive
The variables related to the invitation to the Body Volume Index app are in the file o_indresp_ip:
osdetection, bviappoutc1, bviappoutc2, bviinsthow, bviclklnk, bviopencam, bviscanqr, bviopenas, bvifindapp, bviinst, bviopn, bviaccode, bvilogin, bviappemlhas, bvinotwhy1, bvinotwhy2, bvinotwhy3, bvinotwhy4, bvinotwhy5, bvinotwhy6, bvinotwhy7, bvinotwhy8, bvinotwhy9, bvinotwhy97
The data collected with the app are in the file o_bviapp_ip. Appendix B contains the specification of the app contents as well as screen shots of the app. The table below documents the variables in the file o_bviapp_ip.
Contents of the data file o_bviapp_ip
| Source | Variable | Description |
| Identifier | pidp | Cross-wave person identifier |
| Timestamp | date | Date app measurement completed |
| Profile questions | age | Age |
| sex | Sex. Values: 1 Male, 2 Female | |
| height | Height (cm) | |
| weight | Weight (kg) | |
| active | Activity level. Values: 1 Sedentary, 2 Active, 3 Fit, 4 Very fit | |
| Body | bfat | Body fat (%) |
| measurements | vfat | Visceral fat (litres) |
| whratio | Waist hip ratio | |
| wcirc | Waist circumference (cm) | |
| bmi | Body Mass Index (BMI) | |
| rsnktflr | Right side of the neck to the floor (cm) | |
| lsnktflr | Left side of the neck to the floor (cm) | |
| bonktflr | Back of the neck to the floor (cm) | |
| rmpshldrtflr | Right midpoint of the shoulder to the floor (cm) | |
| lmpshldrtflr | Left midpoint of the shoulder to the floor (cm) | |
| vertcrottfl | Vertical crotch to the floor (cm) | |
| linlgtflr | Left length of inside leg from crotch to floor (cm) | |
| rinlgtflr | Right length of inside leg from crotch to floor (cm) | |
| rhknetflr | Right height of the knee to the floor (cm) | |
| lhknerflr | Left height of the knee to the floor (cm) | |
| nkskinwst | From the neck along the skin to waist (cm) | |
| rwsttflr | Right side of the waist to the floor (cm) | |
| lwsttflr | Left side of the waist to the floor (cm) | |
| rlegtflr | Right Leg length from the outside to the floor (cm) | |
| llegtflr | Left Leg length from the outside to the floor (cm) | |
| fnklegbknk | Front of the neck through the legs to the back of the neck (cm) | |
| lcirctrnk | Left circumference of trunk from the top of the shoulder (cm) | |
| rcirctrnk | Right circumference of trunk from the top of the shoulder (cm) | |
| lengshldr | Length between the shoulders (cm) | |
| circneck | Circumference of neck at the base (cm) | |
| lengneck | Length between two sides of the neck (cm) | |
| rbicpcirc | Right bicep circumference (cm) | |
| lbicpcirc | Left bicep circumference (cm) | |
| relbcirc | Right elbow circumference (cm) | |
| lelbcirc | Left elbow circumference (cm) | |
| rfrarm | Right forearm circumference (cm) | |
| lfrarm | Left forearm circumference (cm) | |
| chstcirc | Chest circumference (cm) | |
| wstcircnrw | Waist circumference at narrowest point (cm) | |
| propwst | Proportion of the waist in the front part of the abdomen | |
| wstwho | Waist circumference to WHO guidance (cm) | |
| propwstwho | Proportion of the WHO waist in the front part | |
| circhipwho | Circumference of the hips at the widest point to WHO guidance (cm) | |
| fpopwhohip | Front proportion of the WHO hip measurement | |
| rcircthgh | Right circumference of the thigh (cm) | |
| lcircthgh | Left circumference of the thigh (cm) | |
| rcircknee | Right circumference of the knee (cm) | |
| lcircknee | Left circumference of the knee (cm) | |
| rclfcirc | Right calf circumference at the widest point (cm) | |
| lclfcirc | Left calf circumference at the widest point (cm) | |
| lclfcircm | circumference of calf at the mid point between knee and floor (cm) | |
| rclfcircm | circumference of calf at the mid point between knee and floor (cm) | |
| rlengft | Right length of foot from base of the heel to the toe (cm) | |
| llengft | Left length of foot from base of the heel to the toe (cm) | |
| Debrief | scan | Who took the photos. Values: 1 I did, 2 Someone else |
| questions | backgrd1 | Background in photos: Furniture |
| backgrd2 | Background in photo: Door(s) | |
| backgrd3 | Background in photos: Window(s) | |
| backgrd4 | Background in photos: Picture(s) | |
| backgrd5 | Background in photos: Mirrors | |
| backgrd6 | Background in photos: Something else | |
| backgrd7 | Background in photos: Nothing, empty wall | |
| wallclr | Colour of background wall. Values: 1 White or off-white, 2 Red, 3 Orange, 4 Yellow, 5 Green, 6 Blue, 7 Purple, 8 Grey, 9 Brown, 10 Black, 11 Multipole colours | |
| wallsd | Shade of background wall. Asked if wallclr is not 1. Values: 1 Light, 2 Medium, 3 Dark | |
| clothes | Type of clothing worn. Values: 1 Underwear, 2 Tight clothing, 3 Baggy clothing, 4 No clothes, 5 Mixture of tight and baggy clothing | |
| light | Lighting when photos were taken. Values: 1 Light, 2 Medium, 3 Dark |
