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Length of time used birth control pills: Number of units

Codes and Frequencies

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For female sample adults ages 18 and older who have ever used birth control pills, BCPILLNO reports the duration of time that the respondent used birth control pills, in number of units. This variable should be used in conjunction with BCPILLTP, which reports the corresponding time period (e.g., days, weeks, months, or years).

BCPILLNO was first introduced in 1987 as part of a supplement on cancer epidemiology. For related variables, please use the IPUMS NHIS search function or drop-down menus.


In 1987, respondents were given the option of reporting duration of birth control pill use in increments of days, months, or years. Beginning in 2000, respondents were also given the option of reporting birth control pill use in increments of weeks. Additionally, in 1987, respondents were explicitly instructed to include any breaks in usage that lasted less than one month. They were not given those instructions in 2000. As a result, researchers should use caution when making comparisons between years. See the Survey Text tab for more details.

Changes in survey design (e.g., quarters in which the supplement was collected) may affect raw frequencies, but do not affect comparability of the variable. Data users are reminded to use the prescribed IHIS weights in their analyses.


  • 1987: Half of female sample persons age 18+ (excluded from CACT) who ever used birth control pills.
  • 2000: Female sample adults age 18+ who ever used birth control pills.


  • 1987, 2000