Many of the graphs on this site display quartiles, which are a useful way of showing how spread out the data is. Quartiles split the data into four equal groups.
The data are first rearranged in ascending order. The lower quartile contains the lowest quarter of the data, the middle quartile contains the bottom half of the data (and is the average (median)) and the upper quartile contains three quarters of the data. The quartiles are calculated using data from all local authorities in England, so, for example, an average (median) will be the average across all local authorities in England.
These are linked to quartiles, and are a way of ranking the data. So, for example, if North Yorkshire has a percentile score of 40% in some measure, 40% of other local authorities are performing worse and 60% are doing better. Sometimes, for instance when looking at the SEN attainment gap, the ranking is reversed and the lower the percentile rank the better the performance, but that will be flagged up on an individual basis.