where is a component common to all siblings in family and is a component unique to i, individual in family which captures individual deviations from the family component. The j i, two components are independent by construction. Thus, the population variance is the sum of the variances of the family and individual components: (3) The covariance between siblings and from the same family, , identifies the variance j j’ component arising from factors shared by siblings. The correlation among randomly drawn pairs of siblings (4) expresses the share of the variance in that can be attributed to family background effects. In y that sense the , is an index of the extent to which inequality in a given sibling correlation, outcome arises from disparities in the families of origin. As pointed out in Bjorklund et al (2002), the correlation coefficient is not estimated directly. Estimates of the variance components used to calculate the correlation are produced. Previous studies of transmission of longevity Table 1. Father-son Brothers Sample characteristics  Corr(,)  Beeton and Various genealogical data sources for wealthy 0.1802 0.1353 0.2853 Pearson classes in Britain over unstated time periods. (1901) Only adult sons used in estimation. Genealogical data from five American families 0.061 Pearl (1931) (Whitney, Hyde, Spooner, and Smedley) and the Durham Town History. Twin analysis using Danish Twin Register McGue et al 0.078-0.329 observations of births 1880-1890: dizygotic (1993) (0.078) and monozygotic (0.329). Gavrilov and Range of 0.09-0.19, increasing in longevity of 0.13 0.151 Gavrilova father. Database of European aristocratic (2001) families. Utah Population Database. Sample restricted to Kerber et al 0.074 individuals who lived past age 65. This estimate (2001) includes parents and children of both genders.
where is a component common to all siblings in family i, and is a component unique to individual j in family i, which captures individual deviations from the family component. The two components are independent by construction. Thus, the population variance is the sum of the variances of the family and individual components: (3) The covariance between siblings j and j’ from the same family, , identifies the variance component arising from factors shared by siblings. The correlation among randomly drawn pairs of siblings (4) expresses the share of the variance in y that can be attributed to family background effects. In that sense the sibling correlation, , is an index of the extent to which inequality in a given outcome arises from disparities in the families of origin. As pointed out in Bjorklund et al (2002), the correlation coefficient is not estimated directly. Estimates of the variance components used to calculate the correlation are produced. Table 1. Previous studies of transmission of longevity Father-son Brothers Sample characteristics  Corr(,)  Beeton and Pearson (1901) 0.1802 0.1353 0.2853 Various genealogical data sources for wealthy classes in Britain over unstated time periods. Only adult sons used in estimation. Pearl (1931) 0.061 Genealogical data from five American families (Whitney, Hyde, Spooner, and Smedley) and the Durham Town History. McGue et al (1993) 0.078-0.329 Twin analysis using Danish Twin Register observations of births 1880-1890: dizygotic (0.078) and monozygotic (0.329). Gavrilov and Gavrilova (2001) 0.13 0.151 Range of 0.09-0.19, increasing in longevity of father. Database of European aristocratic families. Kerber et al (2001) 0.074 Utah Population Database. Sample restricted to individuals who lived past age 65. This estimate includes parents and children of both genders.