Study design and participants
The China COVID-19 survey was an anonymous online study administered from April 25- May 11, 2020 via WeChat, China's leading social networking with more than one billion users. Almost every Chinese adult uses WeChat daily. We used both snowball and convenience sampling to recruit a diverse national sample across China. Data were obtained from 10,545 adults aged 18-80 years old in all 31 province-level administrative units in mainland China. The Institutional Review Board at Xi'an Jiaotong University Health Science Center approved study procedures, and participants provided consent online. An incentive of 1-10 RMB was provided after completing the survey.
Study variables and measurements
The China COVID-19 survey questionnaire included 74 questions.
Mental distress was assessed with a 5-item scale to assess the respondent's mental distress experienced during the COVID-19 pandemic. As we wanted to evaluate symptoms related to COVID-19 stress, we adapted items from the widely used and validated DSM-IV based civilian version of the posttraumatic stress disorder checklist (PCL-C) (14). The scale asks about symptoms in relation to “stressful experiences” and can be used with any population. It measures the intensity of symptoms encountered in the past month: (a) Anhedonia: loss of interest in activities you liked in the past; (b) Sleep problems: difficulty falling asleep, or staying asleep, or waking up frequently or early; (c) Anger: got easily irritable or angry; (d) Difficulty concentrating, and (e) Repeated disturbing dreams related to COVID-19. Response options for each question include a five-point scale from “not at all” to “extremely”. We choose these items based on our pilot study in more than 400 adults in China, which showed that these mental distress symptoms were most frequently reported in adults during the pandemic.
Changes in behavioral outcomes: Changes in PA, smoking, and alcohol consumption were measured by self-reported individual items extracted from Kadoorie Study of Chronic Disease in China (15) and from the China Chronic Disease and Risk Factor Survey (16) developed by the China Center for Disease Control Chronic Disease Control Center. The items, adapted for COVID-19, include: (a) Changes in PA measured by “Has your usual weekly PA changed compare to that before the COVID-19 pandemic?” (b) Change in smoking was measured by “Has your smoking pattern changed compared to that before the COVID-19 pandemic?” (c) Changes in alcohol consumption was measured by “Whether your alcohol consumption has changed compare to that before the COVID-19 pandemic?” Each response used a 5-point Likert scale which ranged from “Increased a lot” =1 to “Reduced a lot” =5; Data analyses on changes in smoking and alcohol consumption were limited to those who were current smokers (n=1,633) and alcohol drinkers (n=2,354) at the time of the survey.
Change in body weight: Participants’ self-reported weight changes (current weight compared to weight prior to the COVID-19 outbreak) were measured. Responses included, “No change (change within 1kg)” =1, “Increased 1-2·5 kg” =2, “Increased>2·5kg” =3, “Decreased 1-2·5 kg” =4, “Decreased>2·5 kg” =5, and “I don’t know” =99.
Other study variables: Associations of socio-demographic and pandemic-related factors with mental distress were examined, and socio-demographic factors were included as covariates in the models for investigating the independent associations of mental distress with behavioral outcomes and body weight. Socio-demographic factors included age, gender, marital status (unmarried, married, cohabiting, widowed, divorced or separated), ethnicity (Han and Not-Han), educational attainment (≤ primary school, secondary school/technical secondary school/technical school, undergraduate/graduate school), current work status (students, have job, jobless, and retirement), residence (urban, town, rural), health insurance (yes, no), and presence of any chronic diseases (e.g., hypertension and diabetes, total number of having chronic diseases were calculated).
Factors related to COVID-19 pandemic included impact on family income (great impact, slight impact, and no impact), impact on daily life due to financial difficulties during the COVID-19 pandemic (great difficulty, slight difficulty, and no difficulty), and loss of job due to COVID-19 (yes, no). All these items were based on a questionnaire developed by Conway and colleagues and used in previous surveys (17). Worry of contracting COVID-19 (not worried at all, a little worried, somewhat worried, and very worried) and perceptions about the likely of contracting COVID-19 (not at all likely, not that likely, somewhat likely, and very likely) were measured with respective single item adapted from a recent COVID-19 awareness, attitude, and action questionnaire (18).
Statistical analysis
First, descriptive analysis was conducted. Then, percentage differences in socio-demographic and pandemic-related factors by mental distress quartile were tested. For descriptive purpose, the quartiles were formed based on the summed score of the five items. χ2 test and ANOVAs were used to compare categorical and continuous variables, respectively.
For inferential analyses, we first evaluated the dimensionality and internal construct validity of mental distress scale using exploratory factor analysis in the overall sample. To account for the ordinal scale of the item responses, poly choric correlations were used in model fitting by treating the ordinal scale for each item as a discretized continuous latent response scale via a probit link. Based on principal components analysis in conjunction with Horn’s parallel analysis (19), one common factor was found to be sufficient for explaining the co variation among the five indicators of mental distress. This one-factor model accounted for 81% of the total variation, with a Cronbach’s alpha of 0.87 (Root Mean Square Error of Approximation (RMSEA)=0·124, 90% confidence interval = 0·117 – 0·131; Comparative Fit Index (CFI)=0·995; Tucker-Lewis Index (TLI)=0·989).
To identify predictors that were associated with mental distress, we fit a structural equation models (SEM) with mental distress factor as the dependent latent variable with covariates including age, sex, marital status, ethnicity, education, health insurance, residence, current work status, household size, body mass index, self-reported health, number of chronic conditions, COVID’s impact on family income, daily life, and job loss, and worries about self or family getting infected. The model was fit using a weighted least square minimum variance estimator.
We fit a SEM that consisted of a factor measurement model for mental distress and a multinomial logistic structural model for associations between mental distress during COVID-19 pandemic and changes in the behavioral outcome and body weight. Age, gender, ethnicity, marital status, educations, residence, and number of chronic conditions were adjusted in all models.
To explore the potential modification of the relationships between mental distress and behavioral changes by pre-COVID-19 factors including age, gender, and educational attainment, multiple-group SEMs were conducted under the assumptions of measurement invariance and structural variance. Separate models were fit for each outcome variable with and without constraining the path coefficient between mental distress and the outcome to be same between levels of the effect modifier. The effect modification was tested using the Satorra-Bentler scaled χ2difference test (20). The SEMs were fit using maximum likelihood with robust standard errors in Mplus version 8.
Analyses were performed by using STATA 16.1 (Stata Corporation, College Station, TX, U.S.), except Mplus version 8.0 was used for SEM. Statistical significance was considered when p<0·05.