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

The data used for this report is provisional and based on an extract taken on 23 May 2022.

At a national level, the outputs of the data quality analyses included in the accompanying data tables, indicate that the figures in this provisional publication are broadly comparable to earlier years.

Table A1 provides a summary of the number of LAs in each region that have submitted data, and Table A2 shows the number of LAs with measurements, as a proportion of those submitted in 2018/19.

 

Full details about validation are provided in NHS Digital’s validation document.
A subset of these validations have been undertaken during the production of these provisional data, details are summarised below.

Local Authorities enter data into the NCMP system which validates each data item at the point of data entry. Invalid data items (e.g. incorrect ethnicity codes) and missing mandatory data items are rejected and unexpected data items (e.g. “extreme” heights) have warning flags added.

During the collection the NCMP system provides each Local Authority with real time data quality indicators, based on the data they have entered, for monitoring and to ensure the early resolution of any issues.

Prior to taking the extract in May, Local Authorities were given an opportunity to review the data they had submitted to the system, enter any measurements for children they had already undertaken, and review and fix any warning messages in the records. This was an optional request, and only those Local Authorities with capacity undertook this exercise.

It is expected that some children who have been measured prior to May 2022 will not be included in this dataset, as some Local Authorities submit all their data later in the year.

Full data quality processes and data submissions will be undertaken when the 2021/22 school year is finalised in the summer of 2022, ahead of producing the final publication for the year.

Table A3 within the accompanying data tables shows the key data quality indicators, at a national level, for this year as at 23 May 2022.

 

This section outlines the data quality work carried out to assess whether the submitted provisional data is representative of the pupil population measured by NCMP in England in terms of sex, deprivation and ethnicity mix.

Comparisons have been made between all provisional data submitted in 2021/22 (the dataset) and all data submitted in 2018/19.  The 2019/20 collection was not complete due to COVID-19 national school closures so data for 2018/19 has been used for comparison as the last full ‘normal’ year.

Tables B to E in the accompanying data tables file cover these analyses:

• Table B: Changes in number of children measured and proportion measured by ethnic group between 2018/19 and 2021/22
• Table C: Changes in number of children measured and proportion measured by child IMD decile between 2018/19 and 2021/22
• Table D: School cohort analyses, by school year, 2018/19 and 2021/22
• Table E: Weighting analyses, by school year, 2018/19 and 2021/22

Further information is provided below.

 

Ethnicity

Overweight and obesity prevalence varies between different ethnic categories, as reported in previous NCMP publications. Therefore, data quality analyses have been undertaken to check whether the provisional dataset is representative by ethnic category.

The proportion of children measured in each ethnic group was compared between 2018/19 and 2021/22 and the following information is included in Table B:

• Number of children measured in 2018/19 and 2021/22 in each ethnic group
• Percentage change in the numbers measured in each ethnic group between years
• Proportion of children in each ethnic group in 2018/19 and 2021/22
• Percentage point change in proportion of children in each ethnic group between years

The proportion of children in each ethnic category varies in both Reception and Year 6. In Reception the largest change was in the White ethnic group showing a 9.1 percentage point decrease compared to 2018/19, followed by the Not Stated category which showed an increase of 8.5 percentage points.

In Reception, the proportion of children in the remaining ethnic categories was similar to 2018/19 with a maximum of 0.8 percentage point change.

The proportion of children measured in each ethnic group in Year 6 was similar between 2018/19 and 2021/22, with the largest change seen in the White ethnic group with a 1.6 percentage point decrease.

BMI prevalence data has not been published by ethnic group in this report, but will be provided in the main report later in the year.

 

Deprivation

Overweight and obesity prevalence is associated with Index of Multiple Deprivation (IMD), as reported in previous NCMP publications. Therefore, data quality analyses have been undertaken to check whether the provisional dataset is representative by child IMD decile.

The proportion of children measured in each IMD decile was compared between 2018/19 and 2021/22 and the following information is included in Table C:

• Number of children measured in 2018/19 and 2021/22 in each IMD decile
• Percentage change in the numbers measured in each IMD decile between years
• Proportion of children in each IMD decile in 2018/19 and 2021/22
• Percentage point change in proportion of children in each IMD decile between years

The proportion of children in each IMD decile varies in both Reception and Year 6, with the two most deprived deciles showing the largest change between years in Reception with a 1.0 percentage point decrease, and second most deprived decile in Year 6 with a 0.7 percentage point decrease.

BMI prevalence data has not been published by IMD decile in this report, but will be provided in the main report later in the year.

 

School Cohort Analyses, 2018/19 and 2021/22

Table D includes the data to accompany this section.

The school cohort analyses are designed to assess the comparability of the provisional data submitted during 2021/22 with the data submitted in 2018/19 by creating subsets of matched school level data. These analyses assume that the children attending the same schools in the two years are likely to share similar characteristics than may be the case in the wider LA. This allows an assessment of any differences that may be present due to sampling a subset of schools in 2021/22. Data was compared for schools that were included in the NCMP in both years and those that were only measured in one year.

Data is presented at national level and separately for underweight, healthy weight, overweight and obese weight categories.

The main information presented in Table D:

• Comparing data for all children in 2018/19 and 2021/22 by weight category and school year
• Comparing data from children in schools that were measured in both years by weight category and school year
• Presenting data from children in schools that were only measured in 2018/19 or in 2021/22, by school year

There are also 3 fields that present information on the changes seen between the groups:

1. Percentage point change in prevalence from 2018/19 to 2021/22 for all children in those years (ALL 2122 - ALL 1819)
2. Percentage point change in prevalence from children in schools that were measured in both years (school cohort)
3. Difference between school cohort and all prevalence change (Field 2 - Field 1)

These outputs allow users to explore any differences in weight prevalence in 2018/19 that existed between the schools that were and were not included in the provisional 2021/22 collection and any bias these differences may have introduced into the provisional 2021/22 dataset; and other similar comparisons that aid interpretation.

At a national level, the data in school cohort and submitted in a single year is very consistent and does not indicate that any substantial bias has been introduced to the provisional 2021/22 dataset due to the subset of schools that were measured up to 23 May 2022, when the extract was taken. This is the case for each of the weight categories: underweight, healthy weight, overweight and obese.

 

 

Weighting Analyses, 2018/19 and 2021/22

Table E includes the data to accompany this section.

The weighting analyses are designed to assess the comparability of the provisional data submitted during 2021/22 with the data submitted in 2018/19 by:

• Comparing data for all children in 2018/19 and 2021/22 (unweighted) by BMI weight categories and change in prevalence
• Comparing data for all children in 2018/19 and 2021/22 (weighted) by BMI weight categories and change in prevalence

This allows an assessment of any differences that may be present due to sampling a subset of schools in 2021/22. 

Data is presented at national level and separately for underweight, healthy weight, overweight and obese weight categories.

There are also 3 fields that present information on the changes seen between the groups:

1. Percentage point change in prevalence from 2018/19 to 2021/22, using unweighted data for 2021/22 (2122 Unweighted - 1819)
2. Percentage point change in prevalence from 2018/19 to 2021/22, using weighted data for 2021/22 (2122 Weighted - 1819)
3. Difference between weighted and unweighted prevalence change (Field 2 - Field 1)

At a national level, the unweighted provisional 2021/22 data is very consistent with the 2021/22 weighted and 2018/19 data, and does not indicate that any substantial bias has been introduced to the provisional 2021/22 dataset due to the subset of schools that were measured up to 23 May 2022, when the extract was taken. This is the case for each of the weight categories: underweight, healthy weight, overweight and obese.

In Reception, obesity prevalence has increased from 9.7% in 2018/19 to 10.4% for unweighted 2021/22 compared to 10.5% for the weighted data. In Year 6, obesity prevalence has increased from 20.2% in 2018/19 to 23.5% for unweighted 2021/22 compared to 23.4% for the weighted data.

Provisional 2021/22 data has been weighted using the same methodology used to weight the 2020/21 data, see weighting methodology section below.

 

Weighting Methodology

The dataset used for this analysis is provisional, so there is a need to assess how representative the pupil population measured by NCMP (National Child Measurement Programme) in England is. Thus, the data is weighted in terms of deprivation and ethnicity mix, using the same methodology as was applied to the NCMP 2020/21 published outputs.

Weighting was carried out on all 2021/22 data submitted to ensure it is comparable to a more normal NCMP year in demography and geography. This allows an assessment of any differences present due to sampling a subset of schools in the provisional 2021/22 data.

The child’s school year (Reception and Year 6), upper tier LA (Local Authority) of school, IMD (Index of Multiple Deprivation) 2019 quintile based on the child’s postcode and grouped ethnicity were investigated as potential weighting variables because they have an association with obesity prevalence.

• Data from the last three complete NCMP years of 2016/17 to 2018/19 was used as the target population (base years) the weighting methodology was trying to achieve.
• Data from three years was used to account for any atypical high or low cell counts from the combination of the weighting values, which may occur if only one year of data was used.
• 2019/20 and 2020/21 data were not used because they were not full NCMP collection years because of COVID-19. In 2019/20 schools closed on 20 March 2020 and in 2020/21 Local Authorities were not required to measure children in all schools.
• The weighting groups used were created using IMD, Upper-tier school LA, Ethnicity and school year (Reception and Year 6).
• The IMD deciles (10 groups) was regrouped into quintiles (5 groups). Where a child’s postcode was missing, the IMD quintile was derived from the postcode of the child’s school. This affected 0.1% of records.
• All Upper-tier LA of school was recoded based on each school’s 2011 LSOA (Lower-layer Super Output Area) to allow comparability across years.
• Ethnicity was regrouped into five groups which comprise of White, Black, Asian, Other and Not Stated/Unknown.

The following flow chart demonstrates, in detail, how weights were calculated for the weighting groups.