To calculate the prisoner population, a 12-month average (based on prisoner counts done at the start of every month) was used where this data was accessible. This data was not accessible for the prisoner population by age or by ethnicity, so quarterly data was used to calculate the prisoner population.
Ethnicity was recorded for more than 95% of incidents of self-harm. Because of the very small number of incidents of self-harm where ethnicity is not known, this data has been excluded from the analysis.
Information is provided by prisons and published by the Ministry of Justice after data checks are completed.
Suppression rules and disclosure control
Values of 2 or fewer prisoners have been suppressed to protect confidentiality. (No incident numbers have been suppressed.)
Rates per 1,000 are rounded to 1 decimal place.