American trade policy towards Sub Saharan Africa –- a meta analysis of AGOA



Table 3: Weighted Least Squares meta regression results

(1)

T-stat

(2)

T-stat

(3)

T-stat

(4)

T-stat

(5)

T-stat

(6)

T-stat

(7)

T-stat

Constant

2.693***

1.932***

-0.253*

-0.572***

-0.406***

-28.82***

-0.360***

(0.077)

(0.079)

(0.101)

(0.097)

(0.109)

(0.001)

(0.006)

no. of explanatory variables

0.0422***

0.0416***

0.0416***

0.0416***

0.0425***

(0.000)

(0.000)

(0.000)

(0.000)

(0.000)

N (in logs)

0.0175***

0.000443

0.00515

-0.00195

-0.0162***

(0.000)

(0.006)

(0.005)

(0.006)

(0.000)

No. of years used (log)

0.0448***

-0.392*

0.0198

-0.269

-0.378***

(0.002)

(0.166)

(0.086)

(0.375)

(0.025)

No. of countries (log)

0.384***

-0.0535***

-0.0642***

-0.0561***

-0.0285***

(0.003)

(0.010)

(0.010)

(0.010)

(0.000)

annual = 1

1.241***

-2.880*

1.092***

(0.190)

(1.214)

(0.031)

selection correction = 1

-0.190***

-0.189***

-0.252***

(0.049)

(0.049)

(0.004)

published = 1

0.0106

2.287*

0.0117***

(0.009)

(0.977)

(0.000)

country effects = 1

-0.283*

0.384

-0.235***

(0.115)

(0.560)

(0.016)

time effects = 1

0.00382

0.0105

-0.00122

(0.046)

(0.048)

(0.004)

cross section = 1

-2.256***

-4.005

-2.485***

(0.320)

(4.257)

(0.044)

other preferences included = 1

0.200***

0.699

0.151***

(0.061)

(3.553)

(0.010)

gravity regression = 1

-0.466***

4.300**

-0.379***

(0.066)

(1.514)

(0.011)

agoa dummy = 1

-2.707***

-2.196***

-2.673***

(0.262)

(0.422)

(0.103)

robust s.e. = 1

-0.144***

-0.139***

0.00619***

(0.016)

(0.017)

(0.001)

product effects = 1

0.153**

-0.864

0.391***

(0.047)

(0.570)

(0.005)

single country analysis = 1

0.834***

0.972***

(0.125)

(0.015)

logged dep. var. = 1

0.288***

-0.116

0.331***

(0.041)

(0.208)

(0.005)

product group = ”All/Total”

-0.00637

-0.0311

(0.056)

(0.068)

product group = ”Apparel & Textiles”

-0.0369

-0.0436

(0.045)

(0.045)

product group = ”Agriculture”

0.0609*

0.0550*

(0.026)

(0.026)

regions included = AGOA countries

-0.0514

-2.874

(0.068)

(3.493)

regions included = AGOA + N. Africa

-0.287***

-6.300**

(0.069)

(2.054)

definition of dep. var. = Exports

-0.214

0.696

(0.264)

(3.502)

definition of dep. var. = Imports

0.156

1.813

(0.245)

(3.455)

time frequency = Annual

0.488**

(0.157)

time frequency = Monthly

-0.0248

-2.959*

(0.134)

(1.208)

econometric method = GMM

-0.00367

-0.657

(0.057)

(0.607)

econometric method = Heckman/Tobit

-0.873***

-2.552

(0.121)

(1.567)

level of aggregation = Aggregate

0.0686+

0.0712+

(0.039)

(0.040)

level of aggregation = Less Aggregate

0.0779*

-2.206*

(0.040)

(0.976)

Precision

0.00449***

-2.228***

2.584***

-0.258+

4.384***

0.0128***

2.489***

(0.000)

(0.009)

(0.342)

(0.149)

(1.056)

(0.000)

(0.107)

Observations

173

173

173

173

173

173

173

goodness of fit-χ2

120496.0

7710.6

862.6

1074.5

836.8

1.31107e+10

316374.3

model χ2

1217.4

114002.8

120850.8

120639.0

120876.6

600194512.9

1.37106e+10

Standard errors in parentheses. All explanatory variables divided by standard error.

The last two columns use the square of the standard error as weights

+ p < 0.1, * p < 0.05, ** p < 0.01, *** p < 0.001

Multi-Level Meta-Regression

The final table, Table (4) below presents the multi-level MRA results. We include these results to check
the robustness of our earlier results given that that our coefficients are nested in the individual studies. The
intercept is the only random component included in the 2-level multi-level
MRA. In column (2) in the table,
precision is negative and significant at the 1% level of significance. The number of explanatory variables,
product fixed effects and logged dependent variables contribute to higher to t-statistics holding all else con-
stant. The remaining significant variables in the final column of the table, number of years, cross-sectional

14



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