National Child Measurement Programme, England 2020/21 School Year

The National Child Measurement Programme (NCMP) was introduced in 2005/06 and collects height and weight measurements of children in reception (aged 4–5 years) and year 6 (aged 10–11 years) in mainstream state-maintained schools in England. Local Authorities are mandated to collect data from these schools. Collection of data from special schools (schools for pupils with special educational needs and pupil referral units) and independent schools is encouraged but data collected from these schools is excluded from the national report.

The programme now holds fifteen years of reliable data and annually measures over one million children. 2019/20 and 2020/21 are atypical collection years and hold fewer measurements due to the COVID-19 pandemic. 2006/07 is the first year the data are considered to be robust due to the low participation in 2005/06.

The NCMP provides robust data for the child excess weight indicators in the Public Health Outcomes Framework (2.06ii - Excess weight in 4-5 and 10-11 year olds), and is a key element of the Government’s approach to tackling child obesity.

The Office for Health Improvement and Disparities  (OHID) has responsibility for national oversight of the programme and Local Authorities (LAs) have a statutory responsibility to deliver it.

NHS Digital has responsibility for the collection, validation and dissemination of NCMP data. OHID make the data available via an interactive analysis tool and also carry out some more detailed analyses.

The national report is accompanied by technical appendices that provide details on:

• Data quality (Methodology and Data Quality section);
• Data collection and validation (Methodology and Data Quality section);
• How BMI classifications are derived (appendix B);
• Guidance on using the data (appendix C);
• Methodology used for confidence intervals (appendix D); and
• Significance testing (appendix E).

This paper aims to provide users with an evidence-based assessment of quality of the statistical output included in this report. 

It reports against those of the nine European Statistical System (ESS) quality dimensions and principles appropriate to this output. In doing so, this meets NHS Digital’s obligation to comply with the UK Statistics Authority (UKSA) Code of Practice for Statistics , and the following principles in particular:

• Trustworthiness pillar, principle 6 (Data governance) which states “Organisations should look after people’s information securely and manage data in ways that are consistent with relevant legislation and serve the public good.”
• Quality pillar, principle 3 (Assured Quality) which states “Producers of statistics and data should explain clearly how they assure themselves that statistics and data are accurate, reliable, coherent and timely.”
• Value pillar, principle 1 (Relevance to Users) which states “Users of statistics and data should be at the centre of statistical production; their needs should be understood, their views sought and acted upon, and their use of statistics supported.”
• Value pillar, principle 2 (Accessibility) which states “Statistics and data should be equally available to all, not given to some people before others. They should be published at a sufficient level of detail and remain publicly available.”

Note: The original quality dimensions are: relevance, accuracy and reliability, timeliness and punctuality, accessibility and clarity, and coherence and comparability; these are set out in Eurostat Statistical Law. However more recent quality guidance from Eurostat includes some additional quality principles on: output quality trade-offs, user needs and perceptions, performance cost and respondent burden, and confidentiality, transparency and security.

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, LAs 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.

Statistical weighting was applied to the data collected 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 body mass index (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.

This dimension covers the degree to which the statistical product meets user needs in both coverage and content.

NCMP covers children aged 4–5 years and 10–11 years attending mainstream state-maintained schools in England.

For each collection year LAs are assigned a list of mainstream state-maintained schools, within their area, along with associated reception and year 6 headcounts (based on Department for Education school census data).

The proportion of returned schools and measured children are assessed at the end of the collection to check that coverage falls within acceptable thresholds. Further information on data quality of key fields in the NCMP dataset is provided in Data Quality Table A.

Coverage against each data item is also assessed and more details are provided in the following section.

Information in the report is presented by the following breakdowns:

• Age;
• Sex;
• Geography (region);
• Deprivation;
• Ethnicity.

This dimension covers, with respect to the statistics, their proximity between an estimate and the unknown true value.

The accuracy and reliability of the dataset underpinning the analyses in the report is ensured by a rigorous validation procedure. Further details are provided in Validation of National Child Measurement Programme data.

As records are submitted, the NCMP system checks that all mandatory data items have been provided and data validation rules have been met.

• Records with missing data items are rejected.
• Invalid data items (e.g. incorrect ethnicity codes) are rejected.
• Unexpected data items (e.g. “extreme” heights) generate warning flags that require LA confirmation.

The NCMP system provides LAs with real-time data quality indicators throughout the collection period. Indicators breaching the data quality thresholds are highlighted. This enables LAs to monitor the quality of their data during the collection period and take action if necessary. The data quality thresholds are provided in the validation document mentioned above. The LA’s NCMP Lead is required to sign off these indicators as part of finalising their data at the end of the collection. Indicators breaching the thresholds require the NCMP Lead to provide a breach reason before it is possible to finalise the submission.

The performance of LAs against these data quality measures is published in Data Quality Table A alongside the national report.

In recognition of the effect of natural year to year variation, confidence intervals are included around the prevalence estimates in the tables and these should be considered when interpreting results. A confidence interval gives an indication of the sampling error around the estimate calculated and takes into consideration the sample sizes and the degree of variation in the data. They are used to determine whether any differences in prevalence figures are likely to be real or due to natural variation.

The sample sizes and participation rates for NCMP are usually large (over one million children measured and a participation rate exceeding 90 per cent for the 2008/09 to 2018/19 collections), so the 95 per cent confidence intervals for prevalence estimates at national level are very narrow. The 2019/20 and 2020/21 collections yielded fewer measurements so have wider, albeit still narrow, confidence intervals (see Table 2 of the report tables). This indicates a small margin of potential error. The comparisons that feature in this report have all been tested at a 95 per cent significance level. Where two figures are described as being different (e.g. higher/lower or increase/decrease etc.) the result of the test has determined a statistically significant difference.  Further details are provided in appendix E of the publication.

As the data are based on a sample (rather than a census) of pupils, the estimates are subject to sampling error. Appendix D details how to calculate sampling errors for this survey, and the excel tables include true standard errors and design effects calculated for key survey estimates.

In general, attention is drawn to differences between estimates only when they are significant at the 95% confidence level, thus indicating that there is less than 5% probability that the observed difference could be due to random sampling variation when no difference occurred in the population from which the sample is drawn.

The limitations of the survey estimates are discussed in appendix C.

Timeliness refers to the time gap between publication and the reference period. Punctuality refers to the gap between planned and actual publication dates.

The NCMP national report is published annually and has never missed a scheduled publication date.

The annual report for 2020/21 is being released just over 3 months from the end of the submission period. The small delay compared to previous years factors in extra time needed to carry out analysis due to the methodology change.

Coherence is the degree to which data which have been derived from different sources or methods but refer to the same topic are similar. Comparability is the degree to which data can be compared over time and domain. 

The report uses the population monitoring thresholds (85th and 95th centiles) of the British 1990 Growth Reference (UK90) to calculate the prevalence of the BMI classifications. This is a common approach used in England to classify children into different BMI categories.

Comparisons of overweight and obesity prevalence figures between the NCMP and other sources can only be made where the other source also uses the population monitoring thresholds of UK90.

The Health Survey for England (HSE) also contains prevalence of different BMI categories.  HSE covers all children and is not restricted to those in reception or year 6 but as it is based on a much smaller sample the confidence intervals around the estimates are much wider than those presented in this report.

A comparison between the data in the 2007/08 NCMP and the HSE 2007, and between the 2008/09 NCMP and the HSE 2008, was published in Chapter 13 of the HSE 2008. 

The report contains links to data published relating to children in Wales, Scotland and Northern Ireland.

Accessibility is the ease with which users are able to access the data, also reflecting the format in which the data are available and the availability of supporting information. Clarity refers to the quality and sufficiency of the metadata, illustrations and accompanying advice.

Learn more about these reports. From 2017/18 reports have been published in HTML format with additional descriptions provided to support users with screen readers. All tables in the report are provided in Excel format.  

The publication may be requested in large print or other formats through the NHS Digital’s contact centre: [email protected]. 

This dimension describes the extent to which different aspects of quality are balanced against each other. 

A small number of children move schools during the school year and therefore can be measured more than once depending on when the measurements take place in the schools they have attended.  This is a necessary trade-off since LAs have a statutory responsibility to measure children in mainstream state-maintained schools regardless of whether these children have been measured previously or not.

This dimension covers the processes for finding out about users and uses and their views on the statistical products. 

This report was part of a consultation on all NHS Digital publications in 2016. There were proposals for changes to this report in section A6.

In response to user feedback gathered from this consultation the report has now been reformatted with extensive written content being replaced by headline results and associated graphics. These presentation techniques are in line with other reports already being produced by NHS Digital which have received positive feedback from users.

The 2015/16 report underwent a review managed by the Government Statistical Service (GSS) Good Practice Team where a team of seven GSS colleagues reviewed the report and made suggestions for improvements. The vast majority of these suggested improvements were implemented.

Ad hoc requests for NCMP data inform the content of published tables during the design and development stage of the publication each year.

NHS Digital is keen to gain a better understanding of the users of this publication and of their needs; feedback is welcome and may be sent to [email protected]. 

This dimension describes the effectiveness, efficiency and economy of the statistical output.

The NCMP operates on an “opt out” basis. Local authorities send letters to parents of children eligible to participate in the NCMP. This letter sets out the purposes for which the data will be held and used and provides an opportunity for the parent to say they do not want their child to be measured. Children not opted out by their parents or by themselves are then measured and their measurements and other details are entered into the NCMP collection system.

The measurement of children's heights and weights, without shoes and coats and in normal, light, indoor clothing, was overseen by healthcare professionals and undertaken in school by trained staff. OHID provides guidance to local authorities on how to accurately measure height and weight.

Data are provided annually by local authorities and published by NHS Digital.  Most local authorities also choose to feedback measurements to parents by generating a letter, using the NCMP collection system, and are encouraged to do so within six weeks of the measurements being taken.

The cost of providing the data centrally was last measured in 2012 and was estimated to be around £131,000.  This was at a time when the data was provided by Primary Care Trusts (PCTs) rather than LAs.  However, it should be a reasonable approximation of the current cost to LAs as the collection has changed little since then.  The cost for NHS Digital to collect, analyse and disseminate the data was around £170,000 in 2020/21.  This includes hosting, maintaining and enhancing the NCMP IT collection system.

The procedures and policy used to ensure sound confidentiality, security and transparent practices.  

This publication is subject to an NHS Digital risk assessment prior to issue which is approved by the NHS Digital Statistical Head of Profession. Information is usually disseminated at a high level of aggregation (lower tier LA level and above).

New disclosure control processes were applied to all outputs in NCMP for 2019/20 and going forwards, however disclosure control was not needed for 2020/21 as data was not published at LA level and regional data published was based on weighted counts.

Full details of the new methodology are available in the methodology change notice.

The data contained in this publication are National Statistics. The code of practice for official statistics is adhered to from collecting the data to publishing.