NIST SP800-22 is a randomness test set applied for a set of sequences. Although SP800-22 is widely used, a rational criterion throughout all test items has not been shown. The main reason is that the dependency of test items has not been perfectly clear. In this paper, a certain scalar is computed for each sequence throughout all test items and make the histogram of the scalar. By comparing the histogram and the theoretical distribution under some assumptions, the dependency is visually shown. In addition, an algorithmic method to derive ``minimum set'' using the histogram is proposed.