  A storm of favorable or critical publications regarding p-values-based
procedures has been observed in both the theoretical and applied literature. We
focus on valid definitions of p-values in the scenarios when composite null
models are in effect. A valid p-value (VpV) statistic can be used to make a
prefixed level-decision. In this context, Kolmogorov Smirnov goodness-of-fit
tests and the normal two sample problem are considered. In particular, we
examine an issue regarding the goodness-of-fit testability based on a single
observation. This article exemplifies constructions of new test procedures,
advocating practical reasons to implement VpV-based mechanisms. The VpV
framework induces an extension of the conventional expected p-value (EPV) tool
for measuring the performance of a test. Associating the EPV concept with the
receiver operating characteristic (ROC) curve methodology, a well-established
biostatistical approach, we propose a Youden index based optimality principle
to derive critical values of decision making procedures. In these terms, the
significance level alpha=0.05 can be suggested, in many situations. In light of
an ROC curve analysis, we introduce partial EPVs to characterize properties of
tests including their unbiasedness. We also provide the intrinsic relationship
between the Bayes Factor (BF) test statistic and the BF of test statistics.
  Keywords: AUC; Bayes Factor; Expected p-value; Kolmogorov Smirnov tests;
Likelihood ratio; Nuisance parameters; P-value; ROC curve; Pooled data; Single
observation; Type I error rate; Youden index
