However, instrumental variable analysis can provide statistically consistent estimates of the effect of an exposure on an outcome even when bidirectional causation or unmeasured common causes of the exposure and outcome may exist (Angrist & Krueger, 2001; Greenland, 2000).
In this study, we present instrumental variable analyses that use natural experiments involving factors that increase risk of childhood maltreatment but are not known to be influenced by or to directly influence nascent sexual orientation (Angrist, Imbens, & Rubin, 1996). Several family characteristics, namely, presence of a stepparent, poverty, parental alcohol abuse, and parental mental illness, are established risk factors for maltreatment (Administration on Children Youth and Families, 2007; Bays, 1990; Ronan, Canoy, & Burke, 2009) but are not plausibly affected by a child’s nascent sexual orientation. We therefore used these family characteristics as instrumental variables to estimate the effect of maltreatment on sexual orientation. Because instrumental variables analyses, to our knowledge, have not been used in sexuality research, we describe the approach here and contrast the assumptions under which our analysis or a conventional analysis could identify the effect of maltreatment on sexual orientation.