title: Conditional estimation in two-stage adaptive designs.
abstract: We consider conditional estimation in two-stage sample size adjustable designs and the consequent bias. More specifically, we consider a design which permits raising the sample size when interim results look rather promising, and which retains the originally planned sample size when results look very promising. The estimation procedures reported comprise the unconditional maximum likelihood, the conditionally unbiased Rao-Blackwell estimator, the conditional median unbiased estimator, and the conditional maximum likelihood with and without bias correction. We compare these estimators based on analytical results and a simulation study. We show how they can be applied in a real clinical trial setting.
authors.affiliation: Division of Cancer Epidemiology, Department of Clinical Sciences Lund, Lund University, Skane University Hospital, Lund, Sweden.
authors.forename: Per
authors.initials: P
authors.lastname: Broberg
authors.affiliation: Department of Statistics, Stockholm University, 10691 Stockholm, Sweden.
authors.forename: Frank
authors.initials: F
authors.lastname: Miller
mesh_terms: D015233:Models, Statistical; D011336:Probability; D012107:Research Design; D018401:Sample Size
keywords: Adaptive design; Conditional estimation; Sample size recalculation; Two-stage design