Several ordinal measures of association for cross-classification tables are compared with respect to their stability when various grids are placed on a bivariate normal distribution. Kendall's taubusually fares better than Kendall's tauc, Goodman and Kruskal's gamma, and three extensions of Spearman's rho for cross-classification tables, in terms of approximating an associated measure for ungrouped data. The loss of efficiency of taubdue to grouping in testing the hypothesis of no association is considered and observed to be strongly related to the proportion of tied pairs of observations.