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Publication, Part of

National Child Measurement Programme, England 2020/21 School Year

Official statistics, National statistics

National Statistics

More detailed description of weighting methodology provided

A more detailed description of the weighting methodology is given in the Methodology and Data Quality, Weighting data section. 

19 July 2022 09:20 AM

Page contents


The National Child Measurement Programme (NCMP) is a key element of the Government’s approach to tackling child obesity by annually measuring children in reception (aged 4–5 years) and year 6 (aged 10–11 years) in mainstream state-maintained schools in England. Independent and special schools are excluded.  See Methodology and Data Quality section for more details.

Child obesity is a good indicator of adult obesity which can lead to poor health outcomes. NCMP data enables local areas to plan services to tackle child obesity and monitor progress.

Local Authorities (LAs) in England measure children in mainstream state-maintained schools during the school year with the programme running between September and August each year to coincide with the academic year. In previous years, over a million children have been measured annually as part of the programme.

Impact of Covid-19 on NCMP 2020/21

Following the disruption to the 2019/20 collection due to the COVID-19 pandemic, NCMP did not officially open as usual at the start of the 2020/21 school year in September 2020, therefore Local Authorities were not required to start collecting child measurement data at this stage.

At the end of March 2021, following a period of school closure, Local Authorities were asked to use the remainder of the academic year to collect a representative sample of child measurement data to enable a national estimate of children’s weight status (including obesity prevalence) for 2020/21 and contribute towards assessing the impact of the COVID-19 pandemic on children’s physical health.

The sample of schools was stratified by deprivation and ethnicity, taking every 9th school, to yield 10% of children in the local area, after factoring in that there could be a higher than normal level of pupil absence. The aim was to have a representative sample of children measured in England in terms of deprivation and ethnicity mix. Many Local Authorities measured in additional schools and data on 299,000 pupils was submitted (approximately 24% of pupils).

Statistical weighting was applied to all the data collected (to retain the most measurements) to produce a dataset representative of the population measured by NCMP in England in previous years. Estimates of body mass index (BMI) classification rates, e.g. the proportion who are obese, are broadly comparable to previous years.

National data tables and reporting shows BMI classification rates with breakdowns by: child age and sex; region; levels of deprivation and ethnicity. The report also contains comparisons over time where appropriate. Data has not been presented at Local Authority level.

The anonymised CSV file and guidance document will not be produced this year.

Confidence intervals, significance and disclosure control

The NCMP dataset is a sample and the prevalence figures in this report are estimates assumed to apply to the entire population. These estimates are subject to natural random variation.

Confidence intervals are quoted in the publication and included in the tables to indicate this variation.  In 2020/21 the sample is much smaller than in earlier years and consequently the confidence intervals, sometimes known as a ‘margin of error’ are wider than in earlier years.

Comparisons between groups and over time have been statistically tested to determine whether differences are likely to be genuine (i.e. statistically significant) or the result of random natural variation. Only statistically significant differences have been described with terms such as “higher”, “lower”, “increase” or “decrease”. When a comparison does not show a statistically significant difference, this will be described using terms such as “similar to” or “the same as".

In the statistical publication text and excel tables, percentages are usually shown to one decimal place. The excel tables contain more decimal places.  Differences are calculated from the unrounded figures in the excel tables and then shown to one decimal place in the text.

Disclosure control rules for NCMP outputs were revised for the 2019/20 publication and details are in the disclosure control methodology change notice. Disclosure control was not required for the 2020/21 data in this publication as data was not published at Local Authority level and regional data published was based on weighted counts.

The report is accompanied by:

  • Data tables and data quality tables, including 95 per cent confidence intervals which should be considered when interpreting results.
  • Methodology and Data Quality section and technical appendices with information on data collection, validation, confidence intervals, statistical testing and the methodologies used for BMI classification rates and for statistical weighting.
Definitions used in the publication

The BMI classification of each child is derived by calculating the child’s BMI centile and classifying as follows:

  • BMI centile <=2: Underweight
  • BMI centile >2 and <85: Healthy weight
  • BMI centile >=85 and <95: Overweight
  • BMI centile >=95: Obese
  • BMI centile >=99.6 Severely obese. Note:  “Severely obese” is a subset of “Obese”. Children with a BMI centile of between 95 and 100 are classified as “Obese” and those with a BMI centile of between 99.6 and 100 are classified as “Severely obese”

This calculation uses age and sex as well as height and weight to take into account different growth patterns in boys and girls at different ages. A child’s BMI centile is a measure of how far a child’s BMI is above or below the average BMI value for their age and sex in a reference population. The NCMP uses the British 1990 growth reference (UK90) to define the BMI classifications.  This approach is recommended by The National Institute for Health and Care Excellence (NICE). See “Calculation of prevalence” in appendix B of the appendices for more details.

The prevalence of children in a BMI classification is calculated by dividing the number of children in that BMI classification by the total number of children and multiplying the result by 100.

Geographical analyses in this report are primarily based on the postcode of the child’s home address which is mapped to a lower super output area.  Some time series analyses use the school postcode as the child postcode was poorly populated in the early years of the NCMP and these are labelled in the report and tables.

Last edited: 17 July 2022 10:54 pm