Academic journal article Population

Estimating Mortality with the Intercensus Cohort Component Method: Application to the Solomon Islands

Academic journal article Population

Estimating Mortality with the Intercensus Cohort Component Method: Application to the Solomon Islands

Article excerpt

On the night of 21-22 November 1999, the Solomon Islands, an island archipelago located east of Papua New Guinea and northeast of Australia, had its sixth population census, counting 409,042 persons. Since the previous census in 1986, the population had increased by 123,866 persons. Most inhabitants depend on subsistence farming and fishing, and only one in five persons aged 14 and older are engaged in paid work in primary sector-related industries or government services (Statistics Office, 1989; 2002).

The Solomon Islands is one of the Pacific island states where the demographic transition is least advanced (Haberkorn, 2004; Pirie, 1994). In the decade before the 1999 census, fertility dropped, but the country trailed behind other countries in the region with a total fertility rate (TFR) of 4.8 (Statistics Office, 2002, Ahlburg, 1996). Similarly, in terms of mortality indicators, the Solomon Islands perform worse than the large majority of Pacific islands countries, even though World Bank mortality figures places the country among the group of more developed countries. Compared with other countries in the region, health services are inadequate and malaria is a particular health threat for children and pregnant women (MOHMS, 1999; Statistics Office, 2002).

This article has two objectives: (1) to report on mortality estimates obtained with standard mortality estimation methods and discuss the inconsistencies which led to the design of an alternative method of mortality estimation; (2) to describe, apply and test this method, named the lntercensus Cohort Component Method (ICCM).

As ICCM requires data on the age-distributions of both censuses as well as data on fertility and international migration, we start out in the next section with a discussion on quality of census data and we estimate levels of fertility and migration. We produce mortality estimates by standard mortality methods and discuss their consistency with the method assumptions and with the indicators of the socio-economic and cultural context. We then present the principles of ICCM, apply them to Solomon Islands census data and assess the plausibility, precision and robustness of the predicted life expectancies. The soundness of ICCM is also tested by applying the method to data of a country (New Zealand) with reliable vital statistics and census data.

I. The quality of census data in the Solomon Islands

1. Population growth and sex ratio

A priori there is no reason to expect any significant difference in coverage between the censuses of 1986 and 1999. Population cooperation with the census was almost universal in both censuses and the procedures used in 1999 were the same as those in 1986, including an elaborate two-visit enumeration system to identify and correct gaps in coverage.

The preparations of both censuses were affected by external events. In 1986, the mapping of enumeration areas on the islands of Guadalcanal and Malaita was disturbed by cyclones leading to postponement of activities so that "census night" had to be shifted back from 1 July to 21-22 November. The 1999 census preparations took place in a period of severe ethnic conflict with large-scale (internal) displacements on Guadalcanal. Fortunately, the census was implemented in a window of calm, while the conflict proper did not actually affect population distribution to any substantial extent, given the small numbers involved and the likelihood that those involved in the conflict would be enumerated in their household of origin. Based on the proper implementation of the two-visit enumeration system in both censuses, and on the fieldwork monitoring and evaluation accounts of both censuses, we conclude that the coverage in both censuses was good and of about the same quality (Statistics Office, 2002).

Application of the Generalized Growth Balance method (Hill, 1987; 2001) to data of both censuses lends support to this conclusion, although we acknowledge that the method cannot prove that the 1999 or 1986 censuses were actually of good quality, as both might have suffered to the same degree from problems such as omissions and double counts. …

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