The Korean version of PHQ-9 was used to measure the sample’s level of depression [32 (link)-34 (link)]. The PHQ-9 including nine items was administered as a self-report measure using a 4-point scale (0=not at all to 3=nearly every day). Higher scores indicated higher depressive levels; the total PHQ-9 scores over 10 indicated moderate or severe depression (cut-off ≥10) [32 (link)-34 (link)]. The total scores of PHQ-9 were used for statistical analysis (ranged 0 to 27). The PHQ-9 in this study showed a high internal consistency at the four survey points (overall Cronbach’s α=0.905).
The covariates were comprised of three blocks to explain the variance of PHQ-9: 1) survey points, 2) demographic variables, and 3) COVID-19 infection fear. As categorical variables, the survey points were assigned by the month of each survey, such as March (time 1; reference), May (time 2), September (time 3), and December (time 4) in 2020. Five demographic variables included gender, age, employment, family types, and regions. Gender was defined as a binary variable: male and female. Age was gauged as years at the point of each survey. Unemployment was coded as 1; others were coded as 0. The sample’s family type was categorized into four attributes: 1) living alone (reference), 2) living with only a partner, 3) living with a partner and child, and 4) other family/co-residence composition. Regions were divided into three attributes: 1) Seoul Capital area (reference), 2) other metropolitan (urban) areas, and 3) provinces (Table 1).
The “COVID-19 infection fear” scale was originally developed and validated by a group of multidisciplinary mental health specialists and researchers (i.e., psychiatry, social welfare, clinical psychology, and nursing) for measuring fear that was directly related to the COVID-19 situation and in consideration of the Korean culture and situations, which distinguished the construct validity from other COVID-19 fear-related measures. Prior to the surveys, the face and content validity of COVID-19 infection fear scale were obtained through several reviews and agreements of 13 mental health specialists and researchers from the multidisciplinary field. The COVID-19 infection fear scale consisted of nine itemsc including: I am afraid that 1) “I may get infected by coronavirus,” 2) “My family members might get infected by coronavirus,” 3) “I may be infected with coronavirus and pass it onto my family members or others,” 4) “I may be infected with coronavirus and will harm others, such as my colleagues at work or school shutdown,” 5) “If I and/or my family get infected, we will be separated/quarantined for treatment,” 6) “I may not be able to receive proper medical treatment,” 7) “I will be stigmatized as a confirmed person of coronavirus infection,” 8) “My community will be stigmatized,” and 9) “I may lose a job or have economic difficulties.” Each item was answered using a 4-point rating (0=very disagree, 1=disagree, 2=agree, and 3=very agree). Higher scores indicated higher levels of fear on COVID-19 infection. The average scores of the COVID-9 infection fear scale were used in the statistical analysis (ranged 0 to 3).d Although the COVID-19 infection fear scale was urgently developed at the early stage of the pandemic, it showed high internal consistency at all survey points (overall Cronbach’s α=0.928) (Table 2).