Demographic and Health Surveys Methodology - Measure DHS

B. In the standard recode file, the reproductive calendar is represented by character strings of fixedlength. Each position within the character string represents a calendar month. Thus the thirdposition may represent March 1995, while the fifth position represents May 1995. To calculatethe durations of the episodes of use, each position is examined in chronological order for acontraceptive code. The first code following a position without that code indicates the start of anew episode of use. The first position is ignored in this examination, since a code in that positionmay represent an episode of use that began before the calendar start date. The number ofcontiguous positions with the same contraceptive code indicates the number of months of use inthe episode. An episode ends if the following position does not have the same contraceptive code(a discontinuation) or corresponds to the month of interview (a censored duration). The episodesare then tabulated by duration and type of ending for each contraceptive method and for allmethods combined. Standard life table calculations are then applied to the terminations tocalculate months of exposure and number of discontinuations by month of episode. Thecumulative proportion that discontinued by 12 months is taken as the 12-month discontinuationrate.C. The discontinuation rate is categorized by type of discontinuation, which is noted in the secondcolumn of the reproductive calendar in the box that corresponds to the month of discontinuation.Discontinuation, by reason of contraceptive failure, is given if the woman became pregnant whileusing contraception. In this case, the box in the first column corresponding to the monthfollowing the termination should include a “P” for pregnancy or a “T” for pregnancy termination(very unlikely to occur). Discontinuation to switch to another method is determined if the box forthe month following the discontinuation of the specific method contains another contraceptivemethod. Discontinuation for switching is also indicated by a code in the second calendar columnthat indicates that the woman wanted a more effective method and that the new method beganwithin two months of discontinuation (i.e., only one month with a ‘0,’ indicating no contraceptiveuse, between episodes of use). Discontinuation of a method, by reason of desire to becomepregnant, is indicated in column 2 by the appropriate code.D. In formulas, the monthly rate of discontinuation, q ij , where i is the number of months since thestart of the episode and j is the reason for discontinuation, is calculated by dividing the number ofepisodes discontinued in month i, d ij , by the total number of episodes that reached duration i,e.;q ijdeijiand the cumulative probability of discontinuing by 12 months duration for reason j isHandling of Missing ValuesQ1212 j 1(1 q ij)i1Use of contraception is not allowed to be missing in any month in the calendar. Missing and unknownreasons for discontinuation are treated as “Other” reasons.Notes and ConsiderationsThe life table calculated is a true multiple decrement table producing net discontinuation rates. Thevarious reasons for discontinuation are treated as competing risks, and the monthly probabilities ofdiscontinuation are additive across the reasons for discontinuation.Guide to DHS Statistics 56 Updated September 2006