Demographic and Health Surveys Methodology - Measure DHS

Medians for discrete variables. These types of medians apply to variables such as number of children,number of prenatal care visits, or in general any discrete variable where the only possible values areintegers. A respondent can only have one, two, or any integer number of children. It is not possible tohave 2.3 children.Medians using the current status data. These types of medians are calculated for variables where 100or close to 100 percent of the population have that characteristic at the beginning of an event and thepercentages diminish as time passes by. For example, 100 percent of children do not know how to walk atbirth. As time progresses, some children begin to walk, and there is an age (in months) where 50 percentor more of the children learn to walk.The calculations for the first three types of medians are calculated in a similar manner and vary basicallyin the final result. Medians using the current status data are calculated using a different methodology. Toillustrate the approach used in calculating the first three types of medians, consider the following table.Variable212223242527Cumulative Percentage182543525863If the variable in question is current age in completed years, the median would be calculated for acompleted period. In this case the interpolation will take place between ages 23 and 24. The result of theinterpolation is (50 – 43)/(52 – 43) + 23 = 23.8, however, one year has to be added because, according tothe completed year definition of age, the cumulative value of 52 percent was reached before completing25 years of age.If the variable were a continuous one, for example, time to a health facility in minutes (for purposes ofsimplicity, time is truncated to the minute). The interpolation would also take place between ages 23 and24, but no adjustment is needed. The median time to a health facility would then be 23.8 minutes.If the variable were of type discrete, the median would be obtained at 24 when 50 percent or more wasreached.Current Status DataCurrent status data are used in DHS to calculate the median duration of breastfeeding, post-partumamenorrhea, and post-partum abstinence. Looking at how the median duration of breastfeeding iscalculated (the same principle applies for amenorrhea and abstinence), information is first obtained on theproportion of children currently being breastfed (for breastfeeding, according to the children’s age inmonths). For purposes of providing some stability to the proportions, the birth data are grouped into twomonthintervals. Before calculating the proportions, the distribution is smoothed by a moving average ofthree groups.Guide to DHS Statistics 17 September 2003