National Child Measurement Programme, England, Provisional 2021/22 School Year Outputs

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.  

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 2021/22 data in this publication as data was only published at a national level.

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.

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 A 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.