Samenvatting
The interaction test for 2 x 2 x t contingency tables of Zelon (1971) is extended to 2 x s x t tables. This test is related to the tests of partial association, or "main effect" of Birch (1965) and Armitage (1966). These tests are frequency analogues of the log-frequency tests considered by Placket (1962) and Goodman (1964). The various analyses are illustrated and compared in several numerical examples.