4.1 Parallel trend test
An important prerequisite for the use of the DID model in policy evaluations is that the experimental group and the control group must have common development trends before the policy is implemented. To verify this condition, we used the parallel trend tests proposed by Beck and Jacobson. As shown in Figure 2, before 2014, the parameter estimation coefficient of the advancement of the industrial structure in the YREB fluctuated around approximately 0, and the confidence interval of the coefficient included 0. This indicates that before the YREB Development Policy was implemented, there was no significant difference between the experimental group and the control group. Therefore, the advancement of the industrial structure passed the parallel trend test. In the three years following the implementation of the policy, AIS showed a clear "U-shaped" development trend, indicating that the implementation of the policy did, in fact, impact the advancement of the industrial structure. Only the year when the policy was implemented and the following two years showed a significant negative impact; subsequently, the policy promoted the industrial structure upgrading process. Then, it returned to the nonsignificant state, indicating that the impact of the YREB Development Policy on industrial structure advancement was temporary and unsustainable.
It can be seen from Figure 3 that before the policy was implemented, the estimated parameter coefficients of the rationalization of the industrial structure all fluctuated around approximately 0, and the confidence intervals of the coefficients all contained 0. This indicates that there was no significant difference between the experimental group and the control group before the implementation of the policy, and the industrial structure rationalization thus passed the parallel trend test. However, following the implementation of the policy, many years of parameter estimates still fluctuated around approximately 0, and the confidence intervals of the coefficients also contained 0. This result suggests that the YREB Development Policy did not play a role in promoting industrial structure rationalization after its implementation. Only in the third year following the implementation of the policy did the policy have a significant inhibitory impact.
4.2 Base regression analysis
Columns (1) and (2) in Table 3 show the base regression results representing the impact of the YREB Development Policy on industrial structure advancement. In column (1), the coefficient of Treat×Time representing the AIS treatment effect was 0.027, which was significant at the 5% level. This means that after the implementation of the YREB Development Policy, the industrial structure advancement in the YREB increased by 2.7%. After adding a series of control variables, the estimated value of the treatment effect coefficient was reduced to 0.017, which was still significant at the 5% level. This result confirmed that the YREB Development Policy did indeed significantly promote industrial structure advancement.
Columns (3) and (4) in Table 3 show the base regression results of the impact of the YREB Development Policy on industrial structure rationalization. The results indicate that before the control variables were added, the coefficient of Treat×Time representing the Theil treatment effect in column (3) was -0.007; this value was not statistically significant. After a series of control variables were added, the Treat×Time coefficient in column (4) was still not statistically significant. This result confirmed that the YREB Development Policy did not significantly affect industrial structure rationalization in the YREB.
In addition, columns (2) and (4) in Table 3 report the impacts of the control variables on the upgrading of the industrial structure. In column (2), except for the level of technological innovation, the other six control indicators all positively impacted industrial structure advancement. In column (4), four control variables significantly affected industrial structure rationalization, namely, the level of economic development, the process of urbanization, the level of opening up, and the level of infrastructure construction.
Table 3 Impact of the YREB Development Policy on the upgrading of the industrial structure
|
(1)
|
(2)
|
(3)
|
(4)
|
Variable
|
AIS
|
AIS
|
Theil
|
Theil
|
Treat×Time
|
0.027**
|
0.017**
|
-0.007
|
0.011
|
|
(2.48)
|
(2.07)
|
(-0.46)
|
(0.88)
|
Economy
|
|
0.100***
|
|
-0.118***
|
|
|
(15.66)
|
|
(-12.72)
|
Urban
|
|
0.068***
|
|
-0.035**
|
|
|
(3.83)
|
|
(-2.35)
|
Open
|
|
0.680***
|
|
-0.979***
|
|
|
(5.29)
|
|
(-5.49)
|
Infrastructure
|
|
0.016***
|
|
-0.067***
|
|
|
(3.15)
|
|
(-10.41)
|
Innovation
|
|
0.199
|
|
17.085***
|
|
|
(0.12)
|
|
(8.17)
|
Government
|
|
0.083***
|
|
-0.014
|
|
|
(3.69)
|
|
(-0.38)
|
Information
|
|
1.165***
|
|
-0.315
|
|
|
(8.16)
|
|
(-1.58)
|
Constant
|
2.228***
|
1.060***
|
0.252***
|
1.717***
|
|
(474.07)
|
(17.17)
|
(35.50)
|
(18.61)
|
Observations
|
3113
|
3113
|
3113
|
3113
|
R-squared
|
0.113
|
0.483
|
0.018
|
0.375
|
Note: *** p<0.01, ** p<0.05, and * p<0.1.
4.3 Robustness test
4.3.1 Placebo test
A series of robustness tests were carried out to ensure the robustness of the results. First, a placebo test was performed by adjusting the time window to construct a dummy policy implementation year. The implementation year of the policy was assumed to be 2008, and data from 2005 to 2011 were selected to examine the impact of the policy on the upgrading of the industrial structure in the YREB. Table 4 shows the results of this test obtained after adjusting the time window. Column (1) shows that before the control variables were added, the AIS coefficient was -0.006, which was not statistically significant. After adding the control variables, the results listed in column (2) were still not statistically significant, contrary to the results listed in Table 3. In addition, the test results of the Theil index showed opposite results. The above results confirm that the study passed the placebo test.
Table 4 Test results obtained after adjusting the time window
|
(1)
|
(2)
|
(3)
|
(4)
|
Outcome var.
|
Ais
|
Ais
|
Theil
|
Theil
|
Before
|
|
|
|
|
Control
|
2.195
|
1.233
|
0.251
|
1.568
|
Treated
|
2.193
|
1.262
|
0.282
|
1.547
|
Diff (T-C)
|
-0.001
|
0.029
|
0.031**
|
-0.021*
|
After
|
|
|
|
|
Control
|
2.220
|
1.213
|
0.239
|
1.614
|
Treated
|
2.212
|
1.228
|
0.304
|
1.633
|
Diff (T-C)
|
-0.008
|
0.015
|
0.066***
|
0.019
|
Diff-in-Diff
|
-0.006
|
-0.014
|
0.035*
|
0.039**
|
Note: *** p<0.01, ** p<0.05, and * p<0.1.
4.3.2 Adjusted sample size
Table 5 shows the test results obtained after adjusting the sample size. Since non-random problems may exist in central cities, the "peripheral cities" method was adopted: the samples of all provincial capitals and four municipalities were eliminated, and the DID test was performed again. We found that after removing these cities, the impacts of the YREB Development Policy on the AIS and Theil index were consistent with the regression results listed in Table 3. This indicates that the inclusion of provincial capitals and municipalities did not cause measurement errors in the test results. Therefore, the results of this test confirm the robustness of our findings.
Table 5 Test results obtained after adjusting the sample size
|
(1)
|
(2)
|
(3)
|
(4)
|
Outcome var.
|
Ais
|
Ais
|
Theil
|
Theil
|
Before
|
|
|
|
|
Control
|
2.199
|
1.214
|
0.275
|
1.782
|
Treated
|
2.198
|
1.226
|
0.330
|
1.803
|
Diff (T-C)
|
-0.001
|
0.012**
|
0.055***
|
0.021***
|
After
|
|
|
|
|
Control
|
2.293
|
1.266
|
0.027
|
1.833
|
Treated
|
2.320
|
1.295
|
0.322
|
1.867
|
Diff (T-C)
|
0.027***
|
0.029***
|
0.046***
|
0.034***
|
Diff-in-Diff
|
0.028***
|
0.017**
|
-0.009
|
0.012
|
Note: *** p<0.01, ** p<0.05, and * p<0.1.
4.4 Heterogeneity analysis
4.4.1 Analysis of population heterogeneity
Due to China's vast territory and large population, great developmental differences exist among regions. Therefore, in this study, we divided the research samples according to the size of the urban population. If the urban population was greater than 5 million, this article defined the urban area as a large city. Cities with populations under 5 million were considered smaller cities. After controlling the control variables, city fixed effect and year fixed effect tests were carried out sequentially, and the regression results are shown in Table 6. The results show that in cities with large urban populations, the YREB Development Policy had a positive impact (coefficient=0.023, p<0.05) on industrial structure advancement. For industrial structure rationalization, the impact of the YREB Development Policy was nonsignificant. For cities with small urban populations, the interaction coefficients of industrial structure advancement and rationalization were both nonsignificant. These results indicate that the implementation of the YREB Development Policy had a more significantly positive impact on industrial structure advancement in cities with large populations than in cities with small populations.
Table 6 Test results of the heterogeneity of the urban population size
|
Population≥500
|
Population<500
|
Variable
|
(1)
|
(2)
|
(3)
|
(4)
|
|
AIS
|
Theil
|
AIS
|
Theil
|
Treat×Time
|
0.023**
|
0.021
|
0.012
|
-0.001
|
|
(2.23)
|
(1.22)
|
(1.22)
|
(-0.06)
|
Control
|
Yes
|
Yes
|
Yes
|
Yes
|
City fixed effect
|
Yes
|
Yes
|
Yes
|
Yes
|
Year fixed effect
|
Yes
|
Yes
|
Yes
|
Yes
|
Constant
|
1.075***
|
1.692***
|
1.150***
|
1.579***
|
|
(16.03)
|
(17.33)
|
(17.22)
|
(16.27)
|
Observations
|
2497
|
2497
|
2552
|
2552
|
R-squared
|
0.511
|
0.394
|
0.452
|
0.356
|
Note: *** p<0.01, ** p<0.05, and * p<0.1.
4.4.2 Analysis of regional heterogeneity
Traditionally, people divide the YREB into upper, middle, and lower reaches based on geographical and economic factors. The upper reaches of the Yangtze River include the four provinces of Yunnan, Guizhou, Sichuan, and Chongqing. The middle reaches include Hunan, Hubei, and Jiangxi Provinces. The lower reaches involve Shanghai, Jiangsu, Zhejiang, and Anhui Provinces. In our article, 107 cities in 11 provinces within the YREB were included as the research objects, and research was carried out according to the heterogeneity among these cities.
Table 7 shows the impact of the YREB Development Policy on the upgrading of the industrial structure across the upper, middle and lower reaches of the YREB. In the upper reaches of the YREB, judging from the coefficient of the interaction term, the implementation of the policy did not have a significant impact (AIS coefficient of -0.005, p>0.1; Theil coefficient of 0.028, p>0.1). In the middle reaches of the YREB, the policy significantly positively impacted industrial structure advancement (AIS coefficient of 0.025, p<0.1) but had a nonsignificant impact on industrial structure rationalization (Theil coefficient of -0.009, p>0.1). In the lower reaches of the YREB, the policy significantly positively impacted industrial structure advancement (AIS coefficient of 0.027, p<0.05) but had a nonsignificant impact on industrial structure rationalization (Theil coefficient of 0.009, p>0.1). It can be seen from these results that the policy more obviously impacted economically active areas and even had restrictions on the transformation and upgrading of the upper and middle reaches.
Table 7 Test results obtained when considering urban heterogeneity
|
The upper reaches
|
The middle reaches
|
The lower reaches
|
Variable
|
(1)
|
(2)
|
(3)
|
(4)
|
(5)
|
(6)
|
|
AIS
|
Theil
|
AIS
|
Theil
|
AIS
|
Theil
|
Treat×Time
|
-0.005
|
0.028
|
0.025*
|
-0.009
|
0.027**
|
0.009
|
|
(-0.40)
|
(1.28)
|
(1.88)
|
(-0.47)
|
(2.57)
|
(0.52)
|
Control
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
City fixed effect
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
Year fixed effect
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
Yes
|
Constant
|
1.202***
|
1.606***
|
1.195***
|
1.519***
|
1.069***
|
1.612***
|
|
(16.89)
|
(16.18)
|
(17.12)
|
(15.68)
|
(16.10)
|
(15.87)
|
Observations
|
2265
|
2265
|
2332
|
2332
|
2386
|
2386
|
R-squared
|
0.484
|
0.423
|
0.450
|
0.351
|
0.510
|
0.366
|
Note: *** p<0.01, ** p<0.05, and * p<0.1.
4.4.3 Analysis of industrial structure change
The above results indicate that the implementation of the YREB Development Policy more significantly impacted industrial structure advancement than industrial structure rationalization. Therefore, this study considered the proportions of the primary, secondary, and tertiary industries in the regional GDP as proxy variables representing industrial structure changes to explore the changes induced by the policy on the industrial structure of the YREB. Columns (1), (2), and (3) in Table 8 successively represent the impacts of the YREB Development Policy on the primary, secondary and tertiary industries in the YREB. In columns (1) and (2), the proportions of the primary and secondary industries decrease following the implementation of the policy, but these decreases are not significant. In contrast, the YREB Development Policy promoted the growth of the tertiary industry (coefficient=0.013, p<0.05). Consequently, this result implies that the development focus of the industrial structure tends to be service-oriented, and this focus benefits the development of the advanced industrial structure.
Table 8 Test results obtained when considering industrial structure changes
Variable
|
(1)
|
(2)
|
(3)
|
|
PI
|
SI
|
TI
|
Treat×Time
|
-0.004
|
-0.009
|
0.013**
|
|
(-1.14)
|
(-1.28)
|
(1.99)
|
Control
|
Yes
|
Yes
|
Yes
|
City fixed effect
|
Yes
|
Yes
|
Yes
|
Year fixed effect
|
Yes
|
Yes
|
Yes
|
Constant
|
0.873***
|
0.194***
|
-0.071
|
|
(29.46)
|
(3.26)
|
(-1.34)
|
Observations
|
3113
|
3113
|
3113
|
R-squared
|
0.585
|
0.297
|
0.328
|
Note: *** p<0.01, ** p<0.05, and * p<0.1.
As clarified above, the YREB Development Policy promoted the development of the tertiary industry in cities in the lower reaches of the YREB and significantly reduced the primary industry proportion in the middle reaches and the secondary industry proportion in the lower reaches. To further determine the roles these control variables play in the upgrading of the industrial structure among different regions, we conducted a deeper analysis of the regional industrial structure changes (see Table 9).
- Economy. In the middle and upper reaches of the YREB, the development speed of the secondary industry is almost two to three times that of the tertiary industry. However, in the lower reaches of the YREB where the economic strength is robust, the development of the secondary and tertiary industries does not differ extensively and is relatively balanced.
- Urban. Accelerating the process of urbanization in the YREB can restrict the development of the primary and secondary industries and can play a sustained and significant role in promoting the tertiary industry. Under this policy shock, the impacts of urbanization on the middle and upper reaches of the YREB were more pronounced than that on the lower reaches. The impacts on the secondary and tertiary industries were obviously more significant than that on the primary industry.
- Opening up. The results show that the impacts of the level of opening up on the three industries in the upper and middle reaches of the YREB were relatively consistent. An increase in the level of opening up significantly reduced the primary and secondary industry proportions and promoted the development of the tertiary industry. Moreover, under the current policy shock, the development of the tertiary industry in the upper reaches of the YREB is better than that in the middle reaches, while the policy has no significant impact on the lower reaches.
- Infrastructure. As shown in Table 9, the higher the level of infrastructure construction is, the more constrained the primary and secondary industries are. The level of infrastructure construction can promote the vigorous development of the tertiary industry. For China, accelerating the infrastructure construction level means promoting the trans-regional flow of resources, and this promotion helps accelerate the regional integration process and is conducive to driving the rapid development of the regional economy.
- Innovation. The empirical results indicate that the implementation of the YREB Development Policy significantly increased the number of patent applications in the primary industry of the YREB and thus improved the technological innovation level of the primary industry. The policy also significantly reduced the enthusiasm of patent applications in the secondary industry.
- Governmental support. In the process of promoting the transformation of the industrial structure, the government has been vigorously developing the primary and tertiary industries. The YREB Development Policy has played an active role in guiding regional modern agriculture and developing the modern service industry. However, the government has significantly reduced its funding support for the secondary industry, which contains a large number of highly energy-consuming industries with underdeveloped production capacities.
- Informatization. One of the intentions of the implementation of the YREB Development Policy was to make full use of the new generation of information technology to transform and upgrade traditional industries and cultivate emerging industries. As shown in Table 9, the positive impact of improved informatization on the industrial structure is embodied in the tertiary industry. Informatization also greatly weakened the primary industry and secondary industry proportions.
Table 9 Test results obtained when considering regional industrial structure changes
Variable
|
The upper reaches
|
The middle reaches
|
The lower reaches
|
(1)
|
(2)
|
(3)
|
(4)
|
(5)
|
(6)
|
(7)
|
(8)
|
(9)
|
PI
|
SI
|
TI
|
PI
|
SI
|
TI
|
PI
|
SI
|
TI
|
Treat×Time
|
0.006
|
-0.008
|
0.003
|
-0.009*
|
-0.007
|
0.016
|
-0.006
|
-0.016*
|
0.023**
|
|
(1.10)
|
(-0.74)
|
(0.25)
|
(-1.88)
|
(-0.64)
|
(1.46)
|
(-1.50)
|
(-1.69)
|
(2.43)
|
Economy
|
-0.069***
|
0.053***
|
0.017***
|
-0.069***
|
0.051***
|
0.018***
|
-0.071***
|
0.040***
|
0.031***
|
|
(-18.72)
|
(8.49)
|
(2.91)
|
(-18.77)
|
(8.36)
|
(3.28)
|
(-19.92)
|
(6.16)
|
(5.46)
|
Urban
|
-0.011*
|
-0.062***
|
0.073***
|
-0.009
|
-0.066***
|
0.075***
|
-0.008*
|
-0.061***
|
0.070***
|
|
(-1.71)
|
(-4.57)
|
(4.27)
|
(-1.47)
|
(-4.75)
|
(4.36)
|
(-1.72)
|
(-5.22)
|
(4.92)
|
Open
|
-0.184***
|
-0.474***
|
0.674***
|
-0.270***
|
-0.234*
|
0.520***
|
-0.100**
|
0.011
|
0.105
|
|
(-3.39)
|
(-3.34)
|
(4.95)
|
(-4.99)
|
(-1.78)
|
(4.02)
|
(-2.06)
|
(0.09)
|
(0.88)
|
Infrastructure
|
-0.006**
|
-0.008*
|
0.014***
|
-0.005*
|
-0.005
|
0.010**
|
-0.005*
|
-0.002
|
0.007*
|
|
(-2.00)
|
(-1.93)
|
(3.22)
|
(-1.87)
|
(-1.12)
|
(2.31)
|
(-1.73)
|
(-0.59)
|
(1.72)
|
Innovation
|
3.433***
|
-4.610***
|
1.236
|
3.463***
|
-4.529***
|
1.129
|
3.586***
|
-4.861***
|
1.314
|
|
(6.27)
|
(-2.76)
|
(0.76)
|
(6.29)
|
(-2.74)
|
(0.72)
|
(7.99)
|
(-3.22)
|
(0.92)
|
Government
|
0.119***
|
-0.308***
|
0.191***
|
0.117***
|
-0.319***
|
0.202***
|
0.121***
|
-0.306***
|
0.185***
|
|
(8.08)
|
(-15.60)
|
(11.32)
|
(7.24)
|
(-15.33)
|
(11.72)
|
(6.92)
|
(-10.57)
|
(8.87)
|
Information
|
-0.205***
|
-0.610***
|
0.805***
|
-0.234***
|
-0.711***
|
0.934***
|
-0.240***
|
-0.724***
|
0.953***
|
|
(-3.50)
|
(-4.73)
|
(6.79)
|
(-4.15)
|
(-5.05)
|
(7.38)
|
(-4.24)
|
(-5.11)
|
(7.54)
|
Constant
|
0.851***
|
0.092
|
0.052
|
0.855***
|
0.097
|
0.044
|
0.867***
|
0.196***
|
-0.067
|
|
(24.81)
|
(1.50)
|
(0.92)
|
(24.69)
|
(1.60)
|
(0.79)
|
(25.37)
|
(2.93)
|
(-1.16)
|
Observations
|
2662
|
2662
|
2662
|
2332
|
2332
|
2332
|
2387
|
2387
|
2387
|
R-squared
|
0.539
|
0.345
|
0.363
|
0.534
|
0.342
|
0.333
|
0.571
|
0.329
|
0.362
|
Note: *** p<0.01, ** p<0.05, and * p<0.1.