*2.3. Measurement*

#### 2.3.1. Demographic Information

Demographic characteristics included age, gender (male/female), marital status (single/married/divorced or widowed), living situation (alone/with spouse, partners or children), medical history of chronic diseases (e.g., heart diseases, diabetes, cancer, respiratory illnesses, liver or kidney diseases), and three key indicators of socioeconomic status (SES) [18,20,23,28]. These included education level (primary school or below/middle or high school/college or above), occupational status (unemployed/pensioner or retired/parttime or full-time employment), and household income (below average/average/above average). Participants were also asked to report their body weight and height for the calculation of body mass index (BMI), using the formula "BMI = body weight (kg)/body height squared (m2)". Based on previous literature, the BMI was categorized by four levels

for Chinese people (underweight: BMI < 18.5; healthy weight: 18.5 ≤ BMI < 23; overweight: 23 ≤ BMI < 26; and obesity: BMI ≥ 26) [30].

#### 2.3.2. Covariates

The acquaintances' disease status and subjective health status served as important covariates for older adult's depression [31,32]. Participants were asked to report the infection situation of COVID-19 of their acquaintances (e.g., friends, family members, and neighbors), as well as their subjective health status (bad/satisfactory/excellent).

#### 2.3.3. Precautionary Behaviors

As recommended by the WHO, the precautionary behaviors for COVID-19 include hand washing, facemask wearing, and social distancing [14]. A six-item structured scale was used to measure the COVID-19 precautionary behaviors, with two items for each of the three behaviors. For example, the items for hand washing were "during the previous week, I adhered to washing my hands with soap and water or alcohol-based hand rub (for at least 20 s, on all surfaces of the hands)" followed by two situations including "(a) in a daily life situation, e.g., before eating, and (b) in a disease-related situation, e.g., after caring for the sick." The items for facemask wearing were "during the previous week, I adhered to wearing a face mask properly" followed by two different situations including "(a) when visiting public places, and (b) when caring for the sick". The items for the social distancing were "during the previous week, I adhered to social distancing" followed by two items including "(a) staying out of crowded places and avoiding mass gatherings when going outside of my home, and (b) keeping space (at least 1.5 m) between myself and other people who are coughing or sneezing." All responses were indicated on a four-point Likert scale ranging from "1 = strongly disagree" to "4 = strongly agree". A mean score of the total six items was calculated.

Participants were also invited to recall their precautionary behaviors before the outbreak of COVID-19 during seasonal influenza (i.e., past precautionary behaviors) using the same scale.
