The convention in reporting contraceptive prevalence is to base this calculation on women married or in sexual union (even though most DHS-type surveys ask questions of contraceptive use to women of reproductive age, regardless of their marital status). In countries with relatively little sexual activity outside marriage for women, basing prevalence estimates on women in sexual union captures the population at risk of pregnancy. However, in countries with the widespread practice of sexual activity outside of marriage or stable sexual unions, a prevalence estimate based on women in union only would ignore a considerable percentage of current users. Thus, researchers and program evaluators generally report percentage of sexually active unmarried women using contraception, if appropriate, in addition to contraceptive prevalence, because method mix is very different for those married versus unmarried (in/not in a stable union).

Whereas evaluators may theoretically derive the CPR from service statistics on numbers of current users and estimates of the population at risk, current practice is to rely upon population-based sample surveys in order to minimize the problems associated with maintaining a running count of current users and with obtaining accurate population estimates. (The problems include incomplete data, double-counting of users who enter the service delivery system at more than one point, purposeful inflation of service statistics, and poor quality of data due to other activities competing for the attention of those recording the information, to name the primary ones.)

The DHS and RHS are currently the main sources for obtaining national level estimates of prevalence. ("DHS" is used in this database to mean "DHS-type surveys:" the actual DHS, the RHS surveys conducted with technical support from CDC, and other large-scale national surveys conducted by the countries themselves under other auspices). Evaluators may also use smaller scale and/or more focused surveys to estimate the CPR as long as they use probability sampling methods, the essential ingredient for obtaining scientifically sound estimates. Evaluators may also obtain CPR by adding relevant questions to surveys on other topics (e.g., health program prevalence or coverage surveys), assuming appropriate sampling methods and sample sizes.