Note that one has to exercise caution in interpreting this result causa - tion ally, since it is at least as plausible that welfare is a determinant of ur- banization. The main purpose of model (6) is to test for the effect of country size by having as many observations in the regression as possible. We therefore had to exclude some variables which were only available for less than 100 countries, but the goodness of fit of the model is still re- markable. All variables in model (6) are highly significant with the ex- ception of the logarithm of population, although trade openness does not appear in the model. We take this result as a further confirmation of our argument concerning the irrelevance of size. The effect of trade openness may be replaced by two variables which are highly correlated with openness, i.e. population density and vulnerability.110Whereas the high correlation between vulnerability and trade openness is not surpris - ing due to the definition of the vulnerability index, there is no apparent 143 
Sources of welfare in VSC 110Pearson correlation coefficients: 0.582 (p < 0.001; two-sided) for openness and pop- dens; 0.690 (p < 0.001; two-sided) for openness and vulnerability. 
            
SourceObs.MeanSt. dev.  Briguglio based on IMF1140.390.27  Baratta (1999)191229.631234.71   Baratta (1999)1916.631.00    World Bank14754.1723.02    Barro-Lee, own195   Barro-Lee, own195    Barro-Lee, own195   Barro-Lee, own195 Barro-Lee118 Barro-Lee1180.080.18  Barro-Lee1330.180.28   Freedom House1893.532.01 Briguglio1140.450.14    Baratta (1999)1593.220.67   Briguglio based on UNCTAD1140.190.24