Sukgumphaphan, Sujin, and Veeranun Pongsapukdee. 2015. “Contingency-Table Sparseness under Cumulative Logit Models for Ordinal Response Categories and Nominal Explanatory Variables With Two-Factor Interaction”. Thailand Statistician 6 (1):27-46. https://ph02.tci-thaijo.org/index.php/thaistat/article/view/34333.