K. Takamatsu, Y. Kozaki, K. Muarakami, K. Bannaka, K. Mitsunari, and Y. Nakata, “NEW ANALYSIS OF VISUALIZATION IN EDUINFORMATICS USING A NETWORK WITH PARAMETRIC AND NONPARAMETRIC CORRELATION COEFFICIENTS WITH THRESHOLD”, pijss, vol. 4, no. 1, pp. 619–630, May 2018.