Demographic and Health Surveys Methodology - Measure DHS

2. For all groups except the first, the midpoint values are one-half month above the lower limit.This midpoint value comes about because the time since birth is calculated as the differencebetween birth dates and the date of interview, which are accurate for month only (day ofmonth is not ascertained).3. For example, if the date of interview were April 2001, the interview could have occurred atany time during the month, from the 1 st to the 30 th . The same holds true for a birth thatoccurred in January 2001, at any time between the 1 st and the 31 st of the month. Thus, thetime difference between the date of birth and the date of interview could be between 60 daysand 120 days. Assuming a constant distribution by day of month for interviews and for births,the midpoint is 90 days or three months, which is the value of the difference in the centurymonthcodes of the dates. The midpoint value for the group of the difference of two monthsand three months together is therefore 2.5.4. The first group is special. The value of the previous group is assumed to be equal to thepercentage of children born 0 to 36 months before the survey who were ever breastfed.Moreover, births that occur in the month of interview can only come before the date ofinterview, rather than on any day of the month of interview. Based on simulations, 0.75 ischosen as the midpoint value for the group < 2 months (0–1). The midpoint of the previousgroup is 0 (day of interview).An example of the median calculation is given below:Example:Group P i Midpoint Width< 2 0.90 0.75 0.752–3 0.70 2.50 1.754–5 0.55 4.50 2.006–7 0.43 6.50 2.00C. MeanMedian duration = 4.5 + (.55 – .5)/(.55 – .43)*(6.5 – 4.5) = 5.33 monthsThe mean duration is the accumulation over all groups of the proportions breastfeeding, exclusivelybreastfeeding, or predominantly breastfeeding multiplied by the width of the time-since-birth group. Forthe first group, the proportion breastfeeding is taken as the proportion ever breastfed for children born 0 to35 months before the survey.mean duration = p i w iHandling of Missing ValuesBirth dates and dates of interview are not allowed to have missing data.Respondents with missing reports of breastfeeding are considered to be not breastfeeding.Guide to DHS Statistics 125 Updated September 2006