An alternative method for calculating relative mobility, inspired by Dahl and DeLeire (2008) and first used by Chetty et al. (2014). Let $R_i$ denote child $i$'s percentile rank in the income distribution of children, and $P_i$ denote parent $i$'s percentile rank in the income distribution of parents. Regressing the child's rank $R_i$ on the parent's rank $P_i$ yields a regression coefficient $\rho_{PR} = Corr(P_i, R_i)$, called the rank-rank slope. The rank-rank slope $\rho_{PR}$ measures the association between a child's position in the income distribution and their parents' position in the distribution. Compared against the intergenerational elasticity of income, the rank-rank slope method has been noted for being more statistically robust.