The present article analyses a classic in the methodology on the analysis of the social variation of languages: the application of the ratio of 0'0025 % to obtain a representative sample of the population of a speaking community. This ratio, established empirically by Labov in 1966 for New York City, nevertheless presents important limitations when moving to communities with smaller populations. Replicating the empirical experimentation in four Spanish populations of different demographic size, it is shown that the empirically representative samples correspond to the confidence intervals already provided by the general statistics. Likewise, it is shown that these were the parameters between which 0,0025 % in the city of New York was developed. Consequently, the problem was not in the formulation of the ratio by Labov (1966), but in the subsequent indiscriminate application that has been made of it.