Half of the world's prison population of about nine million is held in the US, China or Russia.

Prison rates in the US are the world's highest, at 724 people per 100,000. In Russia the rate is 581.

At 145 per 100,000, the imprisonment rate of England and Wales is at about the midpoint worldwide.

Many of the lowest rates are in developing countries, but overcrowding can be a serious problem. Kenyan prisons have an occupancy level of 343.7%