In comparing $K(\geqslant 2)$ treatments in a medical trial, suppose that the response of the patient to treatment is dichotomous. We propose and analyze a class of simple and nondeterministic treatment assignment schemes which tend to put more patients on better treatments. These schemes are also applicable when we have delayed responses from patients.
"The Generalized Polya's Urn Design for Sequential Medical Trials." Ann. Statist. 7 (2) 291 - 296, March, 1979. https://doi.org/10.1214/aos/1176344614