Dangers of using Falconer’s Heritability estimate with typical imaging genetic sample sizes

Aim of Investigation: Heritability is measured with twins studies, where the correlation of monozygotic (MZ, identical) and dizygotic (DZ, fraternal) twins indicates shared variation due to common environmental and/or genetic influences. The simplest estimate of narrow-sense (additive genetic) heritability is Falconer's estimate (Falconer, 1996). Another estimate comes from a components-of-variance approach, where a structured covariance model expresses the shared genetic and environmental effects (Neale, 1998). This approach has much greater flexibility and can be more powerful (Christian, 1995). While best practice in statistical genetics is to use the components-of-variance/SEM approach, Falconer's method is still widely used in imaging genetics studies. The purpose of this work is to demonstrate the poor performance of Falconer's method and demonstrate the limitations of even the best-practice approch at typical sample sizes.