Methodology and Data Source Information

Data sources

The heat maps in this section of the website are based on publicly available data from the Department for Education’s Performance data tables. The maps use performance data at the school and local authority level for three years, 2016/17, 2017/18 and 2018/19.

The information available in the performance data include school information such as postcode, total number of pupils on roll, number of EAL pupils, school type, deprivation (% Free School Meals), and attainment and progress data at Key Stage 2 (KS2) and Key Stage 4 (KS4). Key variables mapped include:

• KS2: Percentage of EAL pupils reaching the expected standard in reading, writing and maths.
• KS2: Reading, writing and mathematics progress.
• KS4: Attainment 8 score.
• KS4: Progress 8 score.

Additional data included in the mapping exercise, at the local authority level:

• The Income Deprivation Affecting Children Index (IDACI).
• English proficiency of EAL pupils¹.
• Descriptive statistics for the key variables are included in Appendix A (below). At the school level, attainment data was available for two thirds of all primary schools in England (66%, n=17,938) and for 70% of secondary settings (n=3,570).
• In KS2, progress data was only available for around a quarter of all primary settings (27%, n=17,938). This skews the available data towards settings with greater proportions of EAL pupils. Two fifths are EAL pupils in the progress sub-sample (40%, n=4,535), compared to the average proportion of EAL pupils overall (16%, n=17,938).
• A calculated variable is included in the analysis, relative attainment which expresses the average attainment of EAL pupils (at the school and local authority level) relative to the average attainment of all pupils. At the school level, this variable is only calculated where we have three full years of data for the numerator and the denominator.²

Methods

Cloud Chamber collated data sets from three years (using the school’s unique reference number) and took a simple mean average of each of the data points. This averaging of data minimises cohort specific variation from the school data, presenting a more consistent set of data at the school level (given some data might be missing).

Note that the data informing the mapping work only includes maintained schools and academies. Independent schools and FE colleges are not available in the performance data and are therefore not included in the analysis. Data is for English schools only.

The maps use the following types of visualisations:

• Choropleth maps: a type of thematic map in which a set of pre-defined areas are coloured in proportion to a statistical variable. We use these maps to visualise a range of data at the local authority level (unitary/upper-tier).
• Heat maps: or a density map use different gradations of colour to represent clustering/density of data points on the map. We use heat maps to visualise school-level data, using postcode information in the performance data.

The main analytical technique is to produce visualisations based on contrasting top and bottom deciles or quartiles of data (top or bottom 10%, or decile, of the distribution). Visualisations are created and hosted in Tableau Public.

The KS2 and KS4 Composite indicator maps combines four factors, equally weighted to indicate where need might be highest among local authority areas. A Z-transformation was used and a simple average of the proportion of pupils who use EAL (%EAL), the attainment of pupils who use EAL, the proportion of pupils who have reached competency or fluency in English, and the proportion of children living in deprived neighbourhoods (IDACI).

Appendix A: Summary data

Summary data for the measures mapped in visualisations. Data is organised by level of aggregation (school and local authority), and key stage.

School level - KS2