*3.2. Measurement*

We utilized a seven-point Likert scale to measure the core variables in this study. All scales of the related variables have been tested in other studies.

Dependent variable: job performance. Based on the research of Williams and Anderson [63], we utilized four items to measure the variable of job performance. Example items include "I am satisfied with my job performance", "I could adequately complete assigned duties" and ""I try to work as hard as possible" (Cronbach's α = 0.858).

Independent variable: Employee mental health. Employee mental health used nine items, mainly from the study of Kashyap and Singh [64]. Example items include "I am always very nervous and feel stressed", "I always feel unhappy or depressed" and "I always could not concentrate when I do something" (Cronbach's α = 0.952).

Mediating variables: Work engagement and employee innovative behavior. First, we used four items to measure work engagement based on the study of Suárez-Albanchez et al. [65]. Example items include "I am passionate about my work", "I feel full of energy when I am working" and "Time flies when I'm working" (Cronbach's α = 0.849). Second, according to the research of Scott and Bruce [66], we used eight items to measure the variable of employee innovative behavior. Example items include "Always search for ideas for new technologies, processes, and/or products", "Always generate creative ideas" and "Always promote and support ideas to others" (Cronbach's α = 0.958).

Control variables: The selection of control variables is important for the results. In this study, firm age, the number of firm employees (firm size), the educational background of employees, and the work experience of employees were set as control variables. Firm age is calculated by the years since the firm was created (1–5 years, 1; 6–10 years, 2; 11–15 years, 3; more than 15 years, 4). Firm size is determined by the number of employees (more than 200 employees, 4; 51–200 employees, 3; 21–50 employees, 2; 20 or fewer employees, 1). Employees' educational background reflects the levels of employees' education (high school degree or below, 1; junior college education, 2; Bachelor's degree, 3; Master's degree, Ph.D., 4). Work experience refers to the year(s) an employee has worked in the company.
