Abstract
The reproductive calendar is a data collection tool that collects month-by-month retrospective histories of contraceptive use. This survey instrument is implemented in large-scale demographic surveys, but its reliability is not well-understood. Our analysis helps to address this research gap, using longitudinal panel data with overlapping calendars from urban Kenya. Our findings indicate calendar data collected in 2014 underestimated 2012 reports of current use by 5 percentage points. And while the overall percentage of women reporting at least one episode of contraceptive use was similar across the two calendars (67 percent vs. 70 percent), there was notable disagreement in contraceptive behavior when comparing the histories of individual women; less than 20 percent of women with any contraceptive use reported the exact same pattern of use in both calendars. Low calendar reliability was especially apparent for younger women and those with complicated contraceptive histories. Individual-level discordance resulted in a small difference in 12-month discontinuation rates for the period of calendar overlap; when surveyed in 2014, women reported a 12-month discontinuation rate of 39 percent, compared to a rate of 34 percent reported in 2012. When using retrospective calendar data, attention must be paid to the potential for individual reporting errors.