Gibrat’s Law for Cities Revisited

The aim of this work is to test empirically the validity of Gibrat’s Law in the growth of cities, using data for all the twentieth century of the complete distribution of cities (without any size restrictions) in three countries: the US, Spain and Italy. For this we use different techniques. First panel data unit root tests confirm the validity of Gibrat’s Law in the upper tail distribution and, second, we find evidence in favour of a weak Gibrat's Law (size affects the variance of the growth process but not its mean) when using non-parametric methods which relate the growth rate to city size. Moreover, the lognormal distribution works as a good description of city size distribution all over the century when no truncation point is considered