the smaller, the higher the degree of downward real
surplus management.
3.2.4 Controlled Variable
Based on previous research results related to equity
pledge and earnings management, the following
variables are used as control variables: (1) Nature of
property rights (SOE): Based on whether it is a state-
owned enterprise, the value is 1 if it is a state-owned
enterprise, and 0 if it is not. (2) Shareholding ratio of
the largest shareholder (Top1): This variable is used
to represent the concentration of ownership. It is
measured by the proportion of the shares held by the
largest shareholder to the total shares of the listed
company. Generally, the larger the proportion, the
higher the degree of equity concentration. (3) Audit
quality (Big4): The Big Four accounting firms are
relatively authoritative accounting firms. It is
measured according to whether the listed company is
audited by the Big Four accounting firm at the end of
the year. (4) Size of the company (Size): The size of
the company is measured by taking the natural
logarithm of the company's total assets. The larger the
indicator is, the larger the company is. (5) Growth
rate of operating income (Growth): It is used to
express the development ability of the enterprise. It is
measured by dividing the operating income of the
current year by the operating income of the previous
year and subtracting one. (6) Number of directors
(Board): Indicates the size of the board of directors of
the listed company, which is measured by taking the
natural logarithm of the number of directors of the
company. (7) Tobin's Q value (Tobin): This variable
is used to measure the company's performance. It is
measured by the ratio of the company's market value
to the replacement cost of assets. At the same time,
two dummy variables of year and industry are defined
to control their effects.
3.3 Model Specification
In this paper, the stepwise test method of mediation
test is used to test whether the total effect coefficient
is significant, that is, whether there is a significant
relationship between the independent variable and the
dependent variable. If significant, proceed to
subsequent analyses, if not, mediation analysis is
terminated. Test whether the effect of the
independent variable acting on the mediating variable
is significant; if it is significant, continue the
subsequent test, otherwise stop the analysis, and the
mediating effect does not exist; test whether the effect
of the mediating variable acting on the dependent
variable is significant; if significant, continue the
subsequent test, otherwise stop the analysis, the
mediating effect does not exist; test whether the direct
effect is significant. When the first two items are
significant, if it is not significant, there is a complete
mediation effect (Judd, Kenny, 1981), otherwise
there is a partial mediation effect (Baron & Kenny
1986).
The following models are set up to conduct the
mediation effect test of assumptions 1,2 and 3, and
then use the Bootstrap method if the step-wise test is
not significant.
Hypothesis 1a、1b was verified to construct the
following multiple linear regression model:
Radinti, t=β0+β1Pledgei, t+β2Soei, t+β3Roai,
t+β4Top1i, t+β5Big4i, t+β6Sizei, t+β7Growthi,
t+β8Boaedi, t+β9Tobini, t+∑Y+∑IND+ε (2)
Hypothesis 2 was verified to construct the
following multiple linear regression model:
Pledgei, t=β0+β1DREMi, t+β2Soei, t+β3Roai,
t+β4Top1i, t+β5Big4i, t+β6Sizei, t+β7Growthi,
t+β8Boaedi, t+β9Tobini, t+∑Y+∑IND+ε (3)
To verify hypothesis 3, the following multiple
linear regression model was constructed by
combining the models (2) and (3):
Radinti, t=β0+β1Pledgei, t+β2DREMi, t+β3Soei,
t+β4Roai, t+β5Top1i, t+β6Big4i, t+β7Sizei,
t+β8Growthi, t+β9Boaedi, t+β10Tobini,
t+∑Y+∑IND+ε
(4)
4 EMPIRICAL ANALYSIS
4.1 Descriptive Statistics
The descriptive statistics of the variables in this paper
are shown in Table 2. The minimum value of R & D
investment of listed companies is 0, and the
maximum value is 251.6%. It can be seen that there
is a large gap in the innovation level of different listed
companies, and there is an extreme phenomenon of
excessive innovation investment in that year. For
example, in Junshi Biology in 2019 and 2020, this
value reached 122.06% and 112.72%. The median is
3.4%, indicating that the overall innovation level of
listed companies is low, and the innovation impetus
is insufficient. The average equity pledge ratio
(Pledge) of controlling shareholders is 44.5%,
indicating that the equity pledge situation of
controlling shareholders of listed companies is
relatively common.
The Variance Inflation Factor test refers to the
ratio of the variance when there is multicollinearity
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