ESTIMATION OF ADULT MORTALITY TRENDS USING ORPHANHOOD METHOD IN MOWE-IBAFO, OGUN STATE

Abstract

The vital registration system, a direct method of estimating mortality, is often incomplete and inaccurate in developing countries. Alternative estimates of reliable mortality indices are needed to assess the impact of health intervention programmes at population subgroups. This study therefore provides estimates of adult mortality level and trends using orphanhood method, an indirect technique, in Mowe-Ibafo area of Ogun State, Nigeria. A cross-sectional study was conducted among 1250 women of reproductive age (15-49 years), selected using a two-stage cluster sampling technique. Six out of 11 clustered communities were randomly selected. All households were visited in each selected cluster and one eligible woman was randomly interviewed in each household. A validated semi-structured questionnaire was used to collect data on respondent's and household member's socio-demographic characteristics, the survivorship status of respondent's parents, number of Children Ever Born (CEB) and those surviving. The socio-demographic data were summarised using descriptive statistics while a periodic cohort was used to project an estimate of CEB and surviving children of the women at the end of their reproductive age. The orphanhood method was used to relate the proportion of respondents with living mothers and fathers to measures of survivorship probabilities by means of multipliers whose values depend on the mean age at childbearing. This was obtained by averaging age of respondents who gave birth within a year before the survey. The adult mortality derived from the complement of survivorship probability is the probability of parents dying from birth to the current age of respondents. Brass and Bamgboye's method of estimating time period in mortality was used to determine adult mortality trends. Abridged life-tables were constructed by linking the survivorship probabilities in childhood and adulthood using the two-parameter logit system. The age of respondents was 30.5±9.0 years with 19.4% in the 25-29 years age group. The sex ratio of household members was 92 males per 100 females. Less than half (46.8%) of the respondents had secondary education. The age at childbearing was 28.5±9.0 years while respondents CEB and surviving children at the end of their reproductive age was 4.14(95% CI: 3.98-4.30) and 3.36(95% CI: 3.12-3.60) respectively. The mortality estimates of respondents' fathers decreased from 0.40 to 0.09 between 1997 and 2004 while it decreased from 0.40 to 0.07 between 1999 and 2004 among their mothers. Life expectancy at birth for male and female were 59.2 and 62.9 years respectively. Also, the life expectancy at age 50 for male and female were 21.7 and 22.1 years respectively. The conditional probability of a male dying between age 15 and 60 years (0.26) was higher than that of females (0.21). Adult mortality estimates declined over the years in Mowe-Ibafo with females having higher. life expectancy than males. There is a need to identify and implement health intervention programmes that will improve the life expectancy, especially among men. Periodic monitoring of adult mortality using orphanhood method in the absence of a reliable vital registration system is also recommended.