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1、实例共同货币对国际贸易实例共同货币对国际贸易影响的影响的MetaMeta分析分析.vIntroductionvMeta-Analysis across studiesvPublication Selection and Meta-Regression AnalysisvConclusionsv My suggestions However,Fishers test for overall effect is inappropiate for this and perhaps all areas of economic research.Why?Because:It is quite stric
2、t It is unlikely to be satisfied by empirical economics.Then other tests for overall effects are needed.(Table 1).We can see:fixed and random effects.Manifestly,there is considerable heterogeneity across studies.The fixed and random effects estimators differ greatly in magnitude and their confidence
3、 intervals dont overlap The smaller fixed effects estimate of gamma indicates currency union raises trade by 33%The random effects estimate indicates this average effect is closer to 90%.Note that all confidence bounds exceed zero What does mean?Positive trade effect Table 2:Reports the fixed-effect
4、s estimates for gamma when studies are omitted from meta-analysis one by one.There is little indication that any single studies is especially influential in driving this result.Again,all confidence bounds are positive(meaning positive trade efect from monetary union).Another important isssue is that
5、 heterogeneity is present not only across studies,but also within most of the individual studies.The random effect estimator is one way to accommodate heterogeneity.And MRA is another way to do it.v Publication Selection and Meta-Regression Analysis:(Critiques)It is possible that these stong finding
6、s may be the artifact of selection for statistical significance(publication bias).Publication Selection occurs when researchers,referees or editors have preference for statistically significant results.Why?Because insignificant findings tend to be suppressed.The problem with such selection is that i
7、t will tend to exaggerate the magnitude of the empirical effect in question,potentially making negligible effects appear important.Funnel graphs:(Important tool)q It is conventional method to identify publication selection.q It is a scatter diagram of precision(1/standard error(SE)versus estimated e
8、ffect.q In the absence of publication selection,the diagram should resemble an inverted funnel(wide at the bottom for small-sample studies,narrowing as it rises)q Asymmetry is the mark of publication bias.qFigure 2 show s lack of symmetry.Funnel graph of 678 individual estimates:q To corroborate thi
9、s pictographic identification of publication bias,we use an MRA of the t-value versus precision.q Publication bias is typically modelled as:q The reason behind this model of publication selection begins with the recognition that researchers will be forced to select larger effects when the standard e
10、rror is also large.q Accounting for likely heterokedasticity leads to the weighted least squares(WLS)version of the previous equation:q In the absence of publication selection,beta o,will be zero.q In table 4:q Beta 0=3.85,which is significantly positive,confirming the asymmetry of the funnel graph.
11、q And we have a MODERATE corroboration of an authentically positive common currency effect(t=1.97)Then,after accommodating publication bias,an economically significant trade effect of monetary union remains.Results:A 95%confidence interval for gamma,after correcting for publication bias,is 0.184-0.5
12、86 Trade is increased between 20 and 80%.v Conclusions:First,the hypothesis that there is no trade effect from currency union is robustly rejected when individual studies are pooled.Second,the pooled estimate is not only positive,but also economically significantThird,there is evidence of publicatio
13、n bias and after correcting this problem we will have a lower trade effect from monetary union.Fourth,as expected,a number of research characteristics are found to have a significant effect on the reported common currency effect.Meta-analysis has an important limitationIf there is a common,systemati
14、c bias across the entire literature,meta-analysis has no way to distinguish it from an a unique empirical effect.v My suggestions:First,to clarify Rose and Stanley question:How much would trade increase when countries have a common currency?(In this case,these countries have always shared it)Second,
15、I wonder another question:How much would trade increase if I introduce a new common currency in these countries?(But in this case,these countries have never shared it)Finally,we could do this analysis in a dynamic way(paying attention to the long term)To see the effect on trade across time when currencies are created and destroyed.QUESTIONS AND COMMENTS THANK YOU VERY MUCH FOR YOUR ATTENTION结束语结束语谢谢大家聆听！谢谢大家聆听！25