Standardized linkage disequilibrium ($D^{\prime }=D/D_{\max }$)

For positive linkage disequilibrium $D$, take $D_{\max }=\min (p_A(1-p_B),(1-p_A)p_B)$; for negative $D$, take $D_{\max }=\min (p_A{p}_B,(1-p_A)(1-p_B))$ and retain its negative sign in $D^{\prime }$. Thus $|D^{\prime }|\le 1$. Its magnitude measures the fraction of the largest disequilibrium possible at the specified allele frequencies. High $|D^{\prime }|$ need not imply high allelic correlation, so it does not alone guarantee good marker prediction.