Counting unreported abortions: A binomial-thinned zero-inflated Poisson model

Abstract

(ProQuest: ... denotes formulae omitted.)1.IntroductionIn most demographic surveys, the number of intentional abortions is significantly underreported. For example, in the National Survey of Family Growth (NSFG), a survey of US women, only 38% of intentional abortions done during the years 20062013 are reported according to the estimates of the National Center for Health Statistics (NCHS). This estimate assumes that the data collected from abortion-service providers through a separate survey is accurate. Reporting rates of intentional abortions at the previous waves of the also have been estimated to be in the range of 35%-48%. Other major surveys of US women, such as the National Surveys of Young Women (NSYW) and the National Longitudinal Surveys of Work Experience of Youth (NLSY), too suffer from this limitation (Jones and Forrest 1992). Underreporting of this magnitude strictly limits the usefulness of self-reported abortion data. The warns that NSFG data on abortion should not be used for substantive research (USDHHS 2014: 35).When intentional abortions are underreported, the total number of reported pregnancies is also automatically underreported, even if other pregnancy outcomes are accurately reported.2 It hinders the accurate estimation of pregnancy timing, contraceptive efficiency, and many other impact-assessment studies in which the number of abortions or pregnancies could potentially be the dependent variable. Nevertheless, in many studies, self-reported abortion counts are analyzed to make strong conclusions while ignoring the impact of underreporting. For example, in Grindlay and Grossman (2013), cross-sectional data from the Department of Defense's survey of health-related behaviors among active-duty military personnel in 2005 and 2008 are analyzed to conclude that the rate of unwanted pregnancies (per 1000 women of reproductive age) has increased from 97 to 105 during the two years, notwithstanding the declared national goal of the government to reduce unwanted pregnancies. They also estimate that the unintended-pregnancy rate in the US military is 50% higher than that rate of the general US population, despite many formal and informal restrictions on sexual relationships faced by women (and men) in the military. Both of these observations could potentially be artifacts of differential reporting rates, across time periods in the first case and among the two groups in second case, due to the differences in the extent of perceived social undesirability of abortion. Another recent study, Tapales and Finer (2015), relies on the assumption that the reporting rates of intentional abortions of different subgroups do not vary across time periods.Some researchers attempt to correct the bias due to underreported abortions before producing a related estimate. Lindberg (2011), another study on the unintendedpregnancy rate in the US military that analyzes data from the same survey as Grindlay and Grossman (2013), assumes that everyone in their sample reports only a fixed percentage of intentional abortions and therefore a fixed percentage of true pregnancies. The unreported pregnancies are assumed to be 11.9% of the number of reported cases based on two previous studies that estimate the reporting rates of intentional abortions in the in comparison to provider surveys. In addition to ignoring the differences in reporting rates across various subgroups, this study simply ignores that the average reporting rate could vary significantly across different surveys.If the reporting rates of intentional abortions are known, preferably at the individual level, it is possible to correct for any potential bias due to underreporting in many studies. When the reporting rate at a particular survey is not known, researchers in most cases simply ignore misreporting, as in Grindlay and Grossman (2013), or use an estimate from a previous study, which may or may not be based on the same survey, as in Lindberg (2011). …