EFFECT OF SAMPLE BIAS ON PALEODEMOGRAPHIC FERTILITY ESTIMATES

Paleodemographers must work to understand how representative any archa eologically recovered skeletal series is and the potential effects of series bias on their demographic reconstructions. We examine two forms of bias: 1) infant underenumeration caused by differential preservati on or incomplete archaeological recovery and 2) the underenumeration o f 45 related to methodological bias. We generated 60 simulated skeleta l series of 250 individuals each leased on the Brass ([1971] Biologica l Aspects of Demography (London: Taylor and Francis), pp. 69-110) legi t models. In the first test, age bias was introduced deterministically for all individuals with age at death over 40 years using the Lovejoy et al. ([1985] Am. J. Phys. Anthropol. 68:1-14) bias estimates. In th e second test, 50% of all individuals under 5 years old were removed f rom each simulated distribution. The simulated series were analyzed us ing the model life table fitting procedure developed by the authors (M ilner et al. [1989] Am. J. Phys. Anthropol. 80:49-58; Paine [1989] Am. J. Phys. Anthropol. 79:51-62). Forms of adult age estimation bias des cribed by Lovejoy and coworkers inflate estimates by 10-20% of the tru e crude birth rate (CBR) (the number of births per year per 1,000 popu lation). Overestimation of fertility and birth rates increases both ab solutely and as a percentage of the true rate as population growth inc reases. This bias is very consistent. Because Lovejoy and colleagues h ave estimated the methodological bias itself: its effects can be estim ated. Infant underenumeration is a more serious obstacle, It is not pr esently possible to estimate infant underenumeration reliably without prior knowledge of fertility rates. This reduces fertility-reconstruct ions based on infant-biased samples to minimum fertility estimates. (C ) 1998 Wiley-Liss, Inc.