“…Our sample was allocated to the strata in proportion to each stratum's population characteristics, such as age, income, and gender, resulting in 22 to 230 households being assigned to each stratum. For example, the numbers of surveys allocated to households in Seoul, Busan, Daegu, Incheon Gwangju, Daejeon, Ulsan, Gyunggi, Gangwon, Chungbuk, Chungnam, Jeounbuk, Jeounnam, Gyungbuk, and Gyungnaum were 197, 71, 50, 55, 30,32,22,230,33,33,45,38,39,58, and 67, respectively. A random sampling was implemented within each stratum.…”