Figure 4.

Sleep duration as a function of the Singh Index in various pair types. This bar plot demonstrates the phenotypic (nongenetically controlled) and within-twin pair (genetically controlled) effect of area-level deprivation on sleep duration in twins. The phenotypic effect is evident comparing the concordant low-SES mean to the concordant high-SES mean (two outermost bars) whereas the attenuation observed within-twin pairs is evident comparing MZ twins discordant for higher vs. lower area-level SES (middle-left two bars). The effect of the Singh Index on sleep duration is less attenuated in discordant DZ twins (middle-right two bars) who share on average only 50% of their genes. DZ, dizygotic; MZ, monozygotic; SES, socioeconomic status.