Fig. 3

Age and sex distribution of the study sample. Ranges are expressed in ISO 31–11 form [A] The form (a,b] expresses the interval a < x ≤ b. For example, (17,29] is used to indicate the set {18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29} of ages in months. Age-heaping, the tendency of respondents to report ages round to the nearest year or six months is common in many settings. This is a major reason why data from nutritional surveys and programs are often analysed and reported using broad age-groups. The commonest age-groups used with children’s data are 6 to 17 months, 18 to 29 months, 30 to 41 months, 42 to 53 months, and 54 to 59 months. These are known as year-centred age-groups. The last age-group covers only six months but is nominally centred at five years.