Title: A Constrained Conditional Likelihood Approach for Estimating the Means of Selected Populations,
Abstract: Given p independent normal populations, we consider the problem of estimating
the mean of those populations, that based on the observed data, give the
strongest signals. We explicitly condition on the ranking of the sample means,
and consider a constrained conditional maximum likelihood (CCMLE) approach,
avoiding the use of any priors and of any sparsity requirement between the
population means. Our results show that if the observed means are too close
together, we should in fact use the grand mean to estimate the mean of the
population with the larger sample mean. If they are separated by more than a
certain threshold, we should shrink the observed means towards each other. As
intuition suggests, it is only if the observed means are far apart that we
should conclude that the magnitude of separation and consequent ranking are not
due to chance. Unlike other methods, our approach does not need to pre-specify
the number of selected populations and the proposed CCMLE is able to perform
simultaneous inference. Our method, which is conceptually straightforward, can
be easily adapted to incorporate other selection criteria.
Selected populations, Maximum likelihood, Constrained MLE, Post-selection
inference