Test of a potential causal influence of earlier age of gambling initiation on gambling involvement and disorder: a multilevel discordant twin design.

The premise that an association between an earlier age of gambling initiation and the later development of disordered gambling is causal has not yet been empirically examined. The current study used a multilevel discordant twin design to examine the nature of this association. Participants were 3,546 same-sex twins (mean age = 37.7 years) from the Australian Twin Registry who completed a telephone interview that included an extensive assessment of gambling and related behaviors. Multilevel models were employed to estimate individual (within-twin-pair comparison) and family level (between-twin-pair comparison) effects, as well as the cross-level interaction between these effects. Family-level effects (genetic or environmental factors shared by family members) of age of gambling initiation robustly predicted later adult gambling frequency and disorder; the evidence for individual-level effects (unique factors not shared by family members, including a potentially causal effect of earlier age of gambling onset) was less robust. The results of this study suggest that the relation between earlier age of gambling initiation and later gambling involvement and disorder is primarily noncausal; efforts to delay the onset of gambling among young people may not necessarily reduce the number who later go on to develop gambling-related problems.