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I am currently trying to find if there is a causal relationship which exists between cuts to government spending and county court judgements.

I have panel data covering multiple regions across 10 years. This data covers: Local authority spending, benefits spending, uneployment, local gross value added (similar to GDP), education, number of county court judements etc... for each region for each year.

I am planning on using a fixed effects regression but I am unsure about whether I should control for both time and entity effects, time effects or just enetity effects.

I have run the regression for entity fixed effects only and for both entity and time fixed effects and the results are pretty different so I am unsure which to use.

Entity Fixed Effects Only

Oneway (individual) effect Within Model

Call:
plm(formula = lg_ccj_p1000 ~ lg_GVA_p_1000 + lg__16._Unemployed_p1000 + 
    lg_low_income_housing_benefits_p1000 + lg_Total_Expenditure_no_Education_p_1000 + 
    lg_Population + lg_Non_Disabled_p_1000 + Dependency.Ratio + 
    lg_Disability_Related.Benefits_p1000, data = df, model = "within", 
    index = c("LACcd", "Year"))

Balanced Panel: n = 149, T = 10, N = 1490

Residuals:
      Min.    1st Qu.     Median    3rd Qu.       Max. 
-0.5712078 -0.1056597 -0.0054156  0.0953477  0.5314735 

Coefficients:
                                          Estimate Std. Error  t-value
lg_GVA_p_1000                            -0.025601   0.084799  -0.3019
lg__16._Unemployed_p1000                 -0.197998   0.023132  -8.5594
lg_low_income_housing_benefits_p1000     -1.445102   0.055498 -26.0387
lg_Total_Expenditure_no_Education_p_1000  0.295909   0.062235   4.7547
lg_Population                            -1.074991   0.297190  -3.6172
lg_Non_Disabled_p_1000                    0.674084   0.201692   3.3422
Dependency.Ratio                         -0.820800   0.388098  -2.1149
lg_Disability_Related.Benefits_p1000     -0.344142   0.079086  -4.3515
                                          Pr(>|t|)    
lg_GVA_p_1000                            0.7627697    
lg__16._Unemployed_p1000                 < 2.2e-16 ***
lg_low_income_housing_benefits_p1000     < 2.2e-16 ***
lg_Total_Expenditure_no_Education_p_1000 2.203e-06 ***
lg_Population                            0.0003090 ***
lg_Non_Disabled_p_1000                   0.0008544 ***
Dependency.Ratio                         0.0346212 *  
lg_Disability_Related.Benefits_p1000     1.455e-05 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Total Sum of Squares:    90.753
Residual Sum of Squares: 34.017
R-Squared:      0.62517
Adj. R-Squared: 0.5813
F-statistic: 277.904 on 8 and 1333 DF, p-value: < 2.22e-16

Both Entity and Time Fixed Effects

Twoways effects Within Model

Call:
plm(formula = lg_ccj_p1000 ~ lg_GVA_p_1000 + lg__16._Unemployed_p1000 + 
    lg_low_income_housing_benefits_p1000 + lg_Total_Expenditure_no_Education_p_1000 + 
    lg_Population + lg_Non_Disabled_p_1000 + Dependency.Ratio + 
    lg_Disability_Related.Benefits_p1000, data = df, effect = "twoways", 
    model = "within", index = c("LACcd", "Year"))

Balanced Panel: n = 149, T = 10, N = 1490

Residuals:
      Min.    1st Qu.     Median    3rd Qu.       Max. 
-0.4704793 -0.0668939 -0.0046179  0.0670402  0.4971985 

Coefficients:
                                           Estimate Std. Error t-value Pr(>|t|)
lg_GVA_p_1000                             0.0099026  0.0594994  0.1664 0.867842
lg__16._Unemployed_p1000                 -0.0079207  0.0177763 -0.4456 0.655976
lg_low_income_housing_benefits_p1000     -0.0435300  0.0680741 -0.6394 0.522641
lg_Total_Expenditure_no_Education_p_1000 -0.0876279  0.0476867 -1.8376 0.066349
lg_Population                            -1.2512911  0.2311960 -5.4123 7.38e-08
lg_Non_Disabled_p_1000                   -0.0206642  0.1505369 -0.1373 0.890838
Dependency.Ratio                         -0.9941714  0.3577568 -2.7789 0.005531
lg_Disability_Related.Benefits_p1000      0.2599478  0.0906636  2.8672 0.004207
                                            
lg_GVA_p_1000                               
lg__16._Unemployed_p1000                    
lg_low_income_housing_benefits_p1000        
lg_Total_Expenditure_no_Education_p_1000 .  
lg_Population                            ***
lg_Non_Disabled_p_1000                      
Dependency.Ratio                         ** 
lg_Disability_Related.Benefits_p1000     ** 
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Total Sum of Squares:    16.771
Residual Sum of Squares: 16.292
R-Squared:      0.028568
Adj. R-Squared: -0.092495
F-statistic: 4.86698 on 8 and 1324 DF, p-value: 6.1864e-06

Any help would be appreciated!

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1 Answer 1

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Although the approach of including both time and unit fixed effects is used often in practice, recent methodological work shows that this approach suffers from problems associated with causal assumptions as well as significant interpretational challenges. Without further assumptions about the nature of the causal effect, you are probably best off employing unit fixed effects with time-varying covariates.

See the following articles for more information:

http://web.mit.edu/insong/www/pdf/FEmatch-twoway.pdf

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0231349

https://www.researchgate.net/publication/334000163_Limitations_of_Fixed-Effects_Models_for_Panel_Data

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