There are two commonly used methods of measuring the incidence of abortion:
The number of abortions performed worldwide seems to have remained stable in recent years, with 41.6 million having been performed in 2003 and 43.8 million having been performed in 2008. The abortion rate worldwide was 28 per 1000 women, though it was 24 per 1000 women for developed countries and 29 per 1000 women for developing countries. The same 2012 study indicated that in 2008, the estimated abortion percentage of known pregnancies was at 21% worldwide, with 26% in developed countries and 20% in developing countries.
On average, the incidence of abortion is similar in countries with restrictive abortion laws and those with more liberal access to abortion. However, restrictive abortion laws are associated with increases in the percentage of abortions which are performed unsafely. The unsafe abortion rate in developing countries is partly attributable to lack of access to modern contraceptives; according to the Guttmacher Institute, providing access to contraceptives would result in about 14.5 million fewer unsafe abortions and 38,000 fewer deaths from unsafe abortion annually worldwide.
The rate of legal, induced abortion varies extensively worldwide. According to the report of employees of Guttmacher Institute it ranged from 7 per 1000 women (Germany and Switzerland) to 30 per 1000 women (Estonia) in countries with complete statistics in 2008. The proportion of pregnancies that ended in induced abortion ranged from about 10% (Israel, the Netherlands and Switzerland) to 30% (Estonia) in the same group, though it might be as high as 36% in Hungary and Romania, whose statistics were deemed incomplete.
The abortion rate may also be expressed as the average number of abortions a woman has during her reproductive years; this is referred to as total abortion rate (TAR).