title: Is the classical Wald test always suitable under response-adaptive randomization?
abstract: The aim of this paper is to analyze the impact of response-adaptive randomization rules for normal response trials intended to test the superiority of one of two available treatments. Taking into account the classical Wald test, we show how response-adaptive methodology could induce a consistent loss of inferential precision. Then, we suggest a modified version of the Wald test which, by using the current allocation proportion to the treatments as a consistent estimator of the target, avoids some degenerate scenarios and so it should be preferable to the classical test. Furthermore, we show both analytically and via simulations how some target allocations may induce a locally decreasing power function. Thus, we derive the conditions on the target guaranteeing its monotonicity and we show how a correct choice of the initial sample size allows one to overcome this drawback regardless of the adopted target.
authors.affiliation: 1 Department of Statistical Sciences, University of Bologna, Italy.
authors.forename: Alessandro Baldi
authors.initials: AB
authors.lastname: Antognini
authors.affiliation: 1 Department of Statistical Sciences, University of Bologna, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Vagheggini
authors.affiliation: 2 Department of Business Administration and Law, University of Calabria, Italy.
authors.forename: Maroussa
authors.initials: M
authors.lastname: Zagoraiou
mesh_terms: D000465:Algorithms; D002986:Clinical Trials as Topic / Q000706:statistics & numerical data; D015986:Confounding Factors, Epidemiologic; D011897:Random Allocation; D018401:Sample Size
keywords: Adaptive experiments; asymptotic tests; comparative clinical trials; ethics; power