Adolescent Problem Gaming and Loot Box Purchasing in Video Games: Cross-sectional Observational Study Using Population-Based Cohort Data - Ide, Soichiro; Nakanishi, Miharu; Yamasaki, Syudo; Ikeda, Kazutaka; Ando, Shuntaro; Hiraiwa-Hasegawa, Mariko; Kasai, Kiyoto; Nishida, Atsushi (JMIR Serious Games, 2021)