p-values

What does the p-value mean for Joinpoint?

Answer:

The Joinpoint Regression Program performs a series of hypothesis tests that test the null hypothesis of ka joinpoints against the alternative hypothesis of kb joinpoints, where ka and kb change for each hypothesis test (ka< kb). Each p-value corresponds to this type of test. The p-value is an estimate of the probability of observing data at least as extreme as the data that we have, in fact, observed under the assumption that the null hypothesis (i.e. smaller number of joinpoints) is true.

As the permutation test is a randomization test, it depends on the random number generator. For greater consistency in the permutation test p-values obtained if one were to change the seed for each run, we suggest running the program for at least 4499 permutations. For this reason, the default number of permutations is now 4499 in the current version of the Joinpoint Regression Program. Choice of the number of permutations selected by the user is a tradeoff between computer time and consistency of the p-values obtained.