m the cohort group.

The total sample obtained from the sampling consists of 2,178 female pensioners. These cohort groups of pensioners were grouped according to the year of retirement from age 55 to 80 years. For the pension year 1990 we have 61 pensioners, 1995 pension year we have 358 pensioners, pension year 2000 we have 670 pensioners and 1,089 pensioners for 2005 pension year.

For the purposes of this study some of the data that have major inconsistences were discarded. These inconsistences include inaccurate or blank date of birth, retirement and death, very late entry into the pensioner category. On the average about 10% of the total population was excluded before arriving at the sample size stated. The total general population was about 120,000 pensioners for both male and female. As at the time of the study, pensioners who have not renewed their life certificate and have had their pension payments seized were assumed dead at the date of last update. Out of the 2,178 female pensioners selected from the general population 424 deaths were recorded.

For confidentiality purpose member identification numbers were removed and data were regrouped to have three essential details; date of retirement, date of death or last update and current age if still alive. Data was further sorted and regrouped to obtain in each target year, age at pension, number of deaths at each age, and the exposed to risk at each age. Pensioners were exposed to investigation from the pension year to June 2014 and were observed from ages 55 to 80 years. The investigation was done only up to age 80 years because after 80 years reported deaths were very scanty and to avoid distorted or misleading results.
3.3: Methodology
Secondary data was used for the research which gives the number of workers who retired at a certain age x to x+1 as the exposed (Ex) within the year. It also counts the number of pensioners who died in a particular year (dx). The crude mortality rate (qx) produced at a particular year is discrete and not smooth. Graduation is done to change the discrete to continuous and for smoothness using Poisson model. But the data on the female mortality has excess zeros which the Poisson model did not fit. A zero inflated Poisson (ZIP) logit model was proposed.