Zubizarreta, José R.; Neuman, Mark; Silber, Jeffrey H.; … - In: Journal of the American Statistical Association 107 (2012) 499, pp. 901-915
In a randomized trial, subjects are assigned to treatment or control by the flip of a fair coin. In many nonrandomized or observational studies, subjects find their way to treatment or control in two steps, either or both of which may lead to biased comparisons. By a vague process, perhaps...
