When are random data not random, or is the PTP test useful?

Recently, empirical evidence was presented that the permutation tail probab ility (PTP) test has extremely low discriminatory power when assessing char acter covariance in phylogenetic data based on bootstrap measures of confid ence. Here we are concerned with the problem of using one statistical appro ach, especially when applied to empirical data, to judge the performance of another. Applying an appropriate statistical approach, we statistically de monstrated that the PTP test is extremely weak in detecting the absence of character covariation. In addition, we show that PTP is highly dependent on the number of terminals and the proportion of character states in phylogen etic matrices. In conclusion, we advocate the use of simulation studies whe n testing the performance of statistical tools applied to phylogenetic data . (C) 2000 The Willi Hennig Society.