School and geographical characteristics included in the analysis
| Type of characteristics | Categories | Notes |
| Religious affiliation* | No religious character | |
| Church of England/other Christian faith excluding Roman Catholic | Includes Anglican, Free Church, Methodist, other Anglican faith, other Christian faith, Plymouth Brethren Christian Church. | |
| Roman Catholic | ||
| Jewish | ||
| Islam/Muslim | ||
| Other | Includes Hindu, Sikh and other. | |
| School type* | State-funded secondary | |
| Independent | ||
| Special school | Combines state-funded and non-maintained schools for children with special educational needs. | |
| Pupil referral unit | Schools for children excluded from mainstream education because of behaviour, sickness or other reasons. | |
| Urban/Rural* | Urban | |
| Rural | ||
| Single sex/mixed* | Mixed | |
| Female | ||
| Male | ||
| School size (number of pupils)† | Up to 400 (small) | Mean headcount was 728 pupils (range 1–2945). |
| >400 to 1000 (average) | ||
| >1000 (large) | ||
| % of population classifying themselves as black or minority ethnic‡ | <5% | Includes any ethnic group other than ‘White: English/Welsh/Scottish/Northern Irish/British, based on 2011 census categories.26 The thresholds are aligned with those used for influenza vaccine coverage school-level analyses in England.13 27 |
| ≥5% and <12% | ||
| ≥12% and <34% | ||
| ≥34% | ||
| Index of Multiple Deprivation 2015‡ | Quintiles | 1 represents the most deprived, 5 the least deprived. Quintiles were obtained by combining published deciles which rank the 32 844 LSOAs in England from most deprived to least deprived and dividing them into 10 equal groups.28 |
*School characteristics.
†School characteristics only used in the mixed-sex, state-funded school-only subanalysis.
‡Lower Super Output Area (LSOA) characteristics.