Computes sample size required for a paired-samples sign test with desired power. The null hypothesis can be expressed in terms of a population proportion. In a paired-samples experiment, the proportion is defined as the proportion of members in the population with scores that would be larger under treatment 1 than treatment 2. In a paired-samples nonexperiment, the proportion is the proportion of members in the population with measurement 1 scores that are larger than their measurement 2 scores. Under the null hypothesis, the population proportion is equal to to .5. This function requires a planning value of the population proportion.