JOINT ESTIMATION OF DOWN-SYNDROME RISK AND ASCERTAINMENT RATES - A METAANALYSIS OF 9 PUBLISHED DATA SETS

In this paper we present an analysis of nine data sets in which ascert ainment and maternal age risk of Down syndrome are estimated jointly u sing maximum likelihood. We include data on 4825 Down syndrome cases f rom nine previously published data sets. These include data from studi es carried out before the introduction of prenatal screening and from recent studies involving women who had not received prenatal testing. Our results show that, allowing for under-ascertainment, there is a go od degree of consistency between the different data sets. We compare t he three-and five-parameter constant plus exponential model with a thr ee-parameter logistic model for maternal age-specific risk. We show th at the three-parameter logistic model provides a good fit to the data and compare rates from this model with those derived from published st udies of uncertain completeness (Cuckle ct al., 1987) and those from d ata sets believed to be complete (Halliday et al., 1995; Hecht and Hoo k, 1994, 1996). In general, our results agree closely with those of th e latter, but achieve greater precision because of the inclusion of ad ditional data. Our derived rates are considerably higher than those of Cuckle et al (1987), which are embedded in many computer systems for generating risks. (C) 1998 John Wiley & Sons, Ltd.