Our statistical principles

We follow certain statistical principles to make sure the data shown on our website is consistent.

Averages: mean and median

The median is the middle point of a range of numbers which are arranged in order.

We usually use the median in our data. Using the median prevents very high and very low values from distorting the figures, but this is less reliable for ethnic groups with smaller numbers of respondents.

The mean is the sum of all the numbers, divided by how many numbers there are.

The mean can be used if there are no very high and very low values that might distort the figures.


Rounding is used to make our published data clearer by making very small changes to the data that do not affect its overall accuracy.


If we were using a base of 5 we would round all the numbers in a dataset up or down to be a multiple of 5. In this example, a value of 26 would be rounded down to 25.

We usually round percentages to 1 decimal place. We round some survey estimates to whole numbers to avoid presenting them as being more accurate than they actually are.