The value of a census cannot be overstated, given that no other data resource provides such detailed information about the population. Further, censuses are often the only historical data source to map out change over time due the consistency of questions asked. However, it is often the most expensive undertaking – other than going to war – that a country embarks on. Countries are thus seeking more cost-effective alternatives. This paper details some exploratory research into one such alternative, based on capture-recapture methods. Capture recapture methods have been used for population estimation for decades, but the focus has been on dual system estimation.
Dual system measurement of the population has been criticized for its reliance on the independence assumption between the two systems. This assumption is untestable, and failure introduces bias into the estimates of the population. The most logical improvement of dual system estimation is triple system estimation. In this paper, a simulation study is carried out to compare the performance of different dual and triple system estimators of the population size under various dependency scenarios. Performance is explored through both the bias and variability. The study shows that the dual system estimator copes well with dependence, provided the coverage of both lists are reasonably high. In addition, although the triple system estimators yield less biased estimates of the population, the dual system estimator is shown to be robust enough to cope with low levels of dependence