  In a novel approach to the multiple testing problem, Efron (2004; 2007)
formulated estimators of the distribution of test statistics or nominal
p-values under a null distribution suitable for modeling the data of thousands
of unaffected genes, non-associated single-nucleotide polymorphisms, or other
biological features. Estimators of the null distribution can improve not only
the empirical Bayes procedure for which it was originally intended, but also
many other multiple comparison procedures. Such estimators serve as the
groundwork for the proposed multiple comparison procedure based on a recent
frequentist method of minimizing posterior expected loss, exemplified with a
non-additive loss function designed for genomic screening rather than for
validation.
  The merit of estimating the null distribution is examined from the vantage
point of conditional inference in the remainder of the paper. In a simulation
study of genome-scale multiple testing, conditioning the observed confidence
level on the estimated null distribution as an approximate ancillary statistic
markedly improved conditional inference. To enable researchers to determine
whether to rely on a particular estimated null distribution for inference or
decision making, an information-theoretic score is provided that quantifies the
benefit of conditioning. As the sum of the degree of ancillarity and the degree
of inferential relevance, the score reflects the balance conditioning would
strike between the two conflicting terms.
  Applications to gene expression microarray data illustrate the methods
introduced.
