To investigate the associations between housing insecurity and mental health, we analyzed the Korea Welfare Panel Study (KoWePS) data between 2007 and 2020. KoWePS has collected information by tracking nationally representative Korean households annually since 2006. KoWePS collects various information, particularly related to individuals’ residential environments and mental health outcomes. The analytic sample, after we cleaned missing and abnormal values for key variables used for our analyses, includes 153,326 observations from 19,396 individuals for 14 years.
Depressive symptoms are our primary outcome. We relied on the Center for Epidemiologic Studies Depression (CES-D 11) scale available to measure the severity of depressive feelings. The CES-D 11 consists of eleven items, including (1) “I lost my appetite,” (2) “I was relatively OK,” (3) “I was very depressed,” (4) “Everything seemed to be overwhelming,” (5) “I could not sleep well,” (6) “I was lonely and felt I was the only one in the world,” (7) “I did not have any complaint,” (8) “Everyone seemed to be mean to me,” (9) “I was sad,” (10) “Everyone seemed to hate me,” and (11) “I did not have the courage to do anything.” Respondents answered each item on a 4-point scale ranging from 0 (rarely or none of the time, less than a day) to 3 (Mostly, 5 ~ 7 days or more a week). Items 2 and 7 are reverse-coded since they indicate the opposite direction of depression. The severity of the symptom is indicated by a total score ranging from 0 to 33, with higher values reflecting greater severity.
Given our focus on the multidimensionality of housing insecurity, we measured it from six different dimensions: (1) housing affordability, (2) housing tenure, (3) residential mobility, (4) overcrowding, (5) poor housing facility, and (6) poor physical environments. First, we measured housing affordability by calculating the proportion of housing-related costs to household income. The total housing-related costs are derived from mortgage-related costs, other loans to pay security deposits, rent, and utility costs. Following previous studies, we categorized housing affordability problems into two types: when housing-related costs account for 30% or more but less than 50% of household income, it is considered housing affordability stress (HAS); and when the costs account for 50% or more of household income, it is severe HAS [28]. Second, we categorized housing tenure into three groups: monthly-paying renters, deposit-only renters (or Jeonse renters in Korean), and homeowners. Korea has a unique tenure system known as Jeonse, which allows tenants to pay a deposit equal to approximately 50–80% of the housing price upfront without paying monthly rent over a contract period. Since Jeonse is commonly regarded as a stepping stone to advance from monthly-paying renting to homeownership, we set Jeonse renters as the reference group, which helps capture the effects of upward/downward changes along with a housing tenure ladder on mental health outcomes. Third, we measured residential mobility based on whether they moved between KoWePS waves. Fourth, we operationalized overcrowding by measuring whether sample households did not meet the official minimum living space requirements per household member set by the Korean government (see the detailed requirements in Appendix 1). Fifth, we regarded poor housing facilities when the sample households’ housing units do not meet at least one of the following conditions: (1) independent water and sewer systems, (2) cooking facilities, (3) toilet facilities, and (4) bathing facilities with hot water. Sixth, we regarded poor physical environments as the housing units that do not meet any of the following criteria: (1) a permanent building made of durable, heat-resistant, fireproof, and moisture-controlled materials, (2) appropriate soundproofing, ventilation, lighting, and heating equipment, (3) suitable for residential use in terms of noise, vibration, odor, or air pollution, and (4) safe from natural disasters such as storms, floods, landslides, or land collapses.
Following previous studies, we included a set of independent variables [15, 29]. First, we categorized the location of residence into four types: (1) Seoul, (2) the Capital region surrounding Seoul (i.e., Gyeonggi and Incheon), (3) metropolitan cities in non-Capital regions, and (4) other areas. We also include variables related to gender, age, age-squared, education attainments, disability status, existing chronic health problems, marital status, the number of children, log-transformed household income, and employment, all of which may influence mental health.
To exploit the advantages of analyzing panel data, we employed a hybrid regression approach, a specific form of conventional fixed-effects models for panel data. The conventional fixed-effects approach cannot estimate the effects of time-invariant factors such as gender, whereas hybrid models combine the advantages of fixed- and random-effects models and simultaneously estimate the effects of time-varying and invariant factors [30]. In hybrid models, all time-varying variables are decomposed into two variables, between- and within-individual variations, and both variables are included in the models. Typically, the estimated coefficients derived from within-individual variations are similar to the estimates from fixed-effects models, whereas the coefficients for time-invariant variables typically reflect underlying contextual effects (see the example in Kang [31]).