The jackknife procedure can be used to compare 2 plant cohorts undergoing different intensities of competition as reflected in the skewness coefficient derived from their above-ground biomass distribution. The results of such comparisons show that the competition experienced by a cohort increases with density and age. The jackknifed skewness coefficient can be obtained by computing different numbers of subestimates of the skewness coefficient for the population. A comparison of the jackknifed results for 6, 12 and n subestimates shows that the jackknifed skewness coefficient is virtually invariant to subgroup size; the jackknife standard error does show variation. A comparison of the jackknife standard error and the standard error when normality is assumed shows, as predicted, that the latter is markedly smaller for heavily skewed plant distributions.