the score is defined as the conditional probability of being assigned to a treatment group given the covariate data, and in practice, it can be estimated from the observed covariate data with a logistic model of the treatment group assignment based on the covariates. The PS used here is instead defined as the conditional probability of being affected given the observed covariate data in families, and its predicted value is then used as the single covariate in Olson's conditional logistic regression model [6]. A covariate-based linkage analysis on the Collaborative Study on the Genetics of Alcoholism (COGA) microsatellite dataset was performed.
