Behavior genetic research on gambling and problem gambling: a preliminary meta-analysis of available data.

A meta-analysis of family and twin studies on gambling and problem gambling was initiated in an effort to determine the probable role of genetic factors in high risk wagering. Two twin studies and 17 investigations employing the family history or family study method were included in this meta-analysis. A summation of the 19 studies produced a small but significant overall effect size (weighted phi = .10, unweighted phi = .13), with both family (weighted phi = .12, unweighted phi = .14) and twin (weighted phi = .06, unweighted phi = .05) studies achieving significant individual mean effects. Given the paucity of twin data, further analysis was confined to family studies and revealed a stronger familial effect for the sons of problem gambling fathers than for the daughters of problem gambling mothers and for more severe forms of problem gambling than for less severe forms of problem wagering, and was strongest for high severity problem gambling in males. The implications of these results are discussed.