*4.1. Overall Influence of Directors' Postgraduate Education Characteristics on a Firm's R&D Investment*

The OLS regression is applied to explore the influence of directors' postgraduate education characteristics on R&D investment in the listed companies. Model 1, model 3, and model 5 are benchmark models that only include independent variables to reflect net influence of directors' education level, discipline background, and graduation institutions on a firm's R&D investment, respectively. Model 2, model 4, and model 6 include three control variables, i.e., corporate asset-liability ratio, industry, and the proportion of directors with work experience in R&D positions. Model 7 involves all the independent and control variables. Table 5 documents the OLS regression results.

As the regression results show, when control variables are introduced based on the benchmark model, the F value and R-value increase prominently, and the F value is statistically significant (p = 0.00). This indicates that the fitting and explanation degree of the model enhances significantly after the introduction of control variables. According to model 2, model 4, model 6, and model 7, the higher the proportion of directors with doctoral degrees is, the more investment in research and development will be made. This result fails to reject the hypothesis 1b. However, proportions of directors with master's degrees, director's discipline background, and graduation institution do not show significant impact on the amount of R&D investment in companies.

The regression coefficient of control variables also manifests the director's R&D working experience, a significantly positive relationship with the firm's R&D investment. However, asset-liability ratio exerts a significantly negative effect on R&D investment. In addition, regression results shown in Table 3 also indicate the industrial heterogeneity of the influence of directors' postgraduate education characteristics on R&D investment in listed companies. Therefore, it is necessary to further run additional regressions by industry.


**Table 5.** OLS regression results of the influence of directors' postgraduate education characteristics on a firm's R&D investment.


**Table 5.** *Cont*.

Note: CC: commercial companies; FR: financial and real estate companies; PU: public utility companies; AFAF: companies in agriculture, forestry, animal husbandry, and fishery; IC: industrial companies; CES: cultural, educational, and sports companies; and IT: IT companies. t statistics in parentheses. \* *p* < 0.1, \*\* *p* < 0.05, \*\*\* *p* < 0.01.
