Datasets and estimation sample

To estimate the impact of providing parents information about the weight status of their child, our analysis is based on two sets of survey data: the main analysis is based on the Millennium Cohort Study (MCS) and the supplementary analysis is on the UK Household Longitudinal Study (UKHLS). Survey data are linked to data on the dates of school visits for the NCMP measurement. We further link administrative data on individual child test scores to data on the dates of school visits. Test scores are from the National Pupil Datasets (NPD) which we briefly describe in section 3.6.5.

Millennium Cohort Study

The Millennium Cohort Study is a UK longitudinal birth cohort study run by the Centre for Longitudinal Studies. The MCS tracks the lives of around 19,000 children born around the Millennium from birth into adulthood.57 The MCS represents all four UK countries, oversampling deprived areas and areas with high concentration of Black and Asian families. The study gathers information on the cohort children’s siblings and parents and covers a wide range of topics such as parenting, childcare, child cognitive development, child and parental health, parents’ employment and education, income and poverty, social capital and ethnicity.

The focus of this paper is on England where the first MCS survey (MCS1) took place between June 2001 and September 2002 when the cohort babies were as close as possible to 9.5 months of age. The second survey (MCS2) was carried out in the same months of the year, when the children were around 3 years old (2003/2005). The next sweeps took place at age 5 (MCS3), age 7 (MCS4), age 11 (MCS5) and age 14 (MCS6) during the child’s first, third, sixth

57 _{There were drop-offs in sample size over time with an achieved sample at age 3 of around 15,000 children}

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and ninth year of compulsory schooling. To cover the academic year, which in England runs from September of one year to August of the next, fieldwork was scheduled to take place between the months of January and July of each of the academic years 2005/06, 2007/08, 2011/12 and 2014/15. When the MCS cohort children were in their 6th school year in the academic year 2011/12 and were interviewed for the MCS fifth sweep, they were also weighed and measured in schools through the NCMP and their parents subsequently received feedback letters. Importantly, these children were weighed and measured through the NCMP in their reception year in 2005/06, but feedback letters had not been implemented then so that parents received no information about the weight outcome.

The number of productive interviews in the MCS5 in England was 8,792, of which 8,720 were with children in Year 6.58 Of these, 7,208 children were merged to the date of NCMP school visit (non-merged cases occur for children who are home schooled or in independent schools, or as a result of incorrect school codes on either of the two data sets). As we apply a difference-in-difference design, which is described in detail in the next section, we only consider those children who also participated in the fourth sweep of the MCS when children were in Year 2. This reduces the sample to 6,524 children. We also exclude those children who were interviewed within 42 days after the school visit as it might take up to 6 weeks to deliver letters (964 children), giving a final sample of 5,560 children (63.2% of the original sample) or 11,120 observations in total across the two time periods. Table C2.1 shows summary statistics of the original sample of all children in the MCS5 in England and of the final estimation sample. As we can see, the estimation sample is very similar to the original one in terms of child, mother, and household characteristics as well as region of residence, settlement type (urban/rural) and decile of overall neighborhood deprivation.

UK Household Longitudinal Study

The UKHLS originally included approximately 40,000 households or 100,000 individuals, covering people of all ages on a wide range of topics such as family life, education, employment, finance, health and wellbeing. We are particularly interested in a special questionnaire, the youth self-completion questionnaire, developed for children aged 10-15 that includes questions on family and the relationship with parents, time allocation, school, health,

58 _{91% of interviews were collected within the timetable fieldwork between January 2012 and July 2012 while}

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nutrition, how children see themselves as a person and how they feel about different aspects of their life.

Despite the great variety of questions that are relevant for our study, we do not use the UKHLS for the main analysis because the majority of questions for youth that are related to our research are asked once every two years. This prevents us from applying a difference-in- difference approach as the majority of the questions that are asked at age 11 (when children are in Year 6 and participate in the NCMP) are not asked at age 10 when children first join the youth panel. Nevertheless, we use the UKHLS to produce some descriptive evidence.

For the descriptive analysis we choose those variables that complement the outcomes available in the MCS. We use a group of questions on how children feel about different aspects of their life such as school, school work, appearance, family, friends, and life as a whole. Children are asked to respond on each question on a likert scale of 1 to 7, where 1 is “not at all happy” and 7 is “completely happy”. For every life aspect we create a dummy variable that combines negative answers (values 1, 2, 3) and neutral answer (value 4) into value 0 and positive answers (values 5, 6, and 7) into value 1. We also create a dummy variable on dieting based on the question whether the child ever tried a diet, where 1 indicates that the child has been on a diet and 0 indicates that the child has never been on a diet.

Based on the UKHLS waves 1-8, there are 3,829 children in England in Year 6 with information on the youth questionnaire. After merging these observations with the school visit data and excluding those children who were interviewed within 6 weeks after the NCMP measurement, the number of observations reduces to 2,435 (63.6% of the initial sample). Table C2.2 shows that based on observable characteristics the final estimation sample is very similar to the original one.

The National Child Measurement Programme Data

Once every academic year, every primary school in England is visited by the bodies implementing the NCMP visits, and we have data on the timing of each school visit. The data was obtained from the Health and Social Care Information centre (NHS Digital), which is the national provide of information, data and IT systems in health and social care in England. Our NCMP data extract covers the 2011/12 academic year. PCTs had flexibility during the school year over when they delivered the NCMP measurements, but had to follow some time frames, including informing parents at least 2 weeks in advance of the measurements and submitting all results by August following the end of the school year. Our survey and NCMP date were merged for us by the Centre for Longitudinal Studies team, using school identifiers.

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