Colleagues Consider:smokers? <- c( 83, 90, 129, 70 ) patients <- c( 86, 93, 136, 82 ) prop.test(smokers, patients) ??? 4-sample test for equality of proportions ?? ?without continuity correction data:? smokers out of patients X-squared = 12.6, df = 3, p-value = 0.005585 alternative hypothesis: two.sided sample estimates: ?? prop 1??? prop 2??????? prop 3??????? prop 4 0.9651163 0.9677419 0.9485294 0.8536585 Now:prop.trend.test(smokers, patients)??? Chi-squared Test for Trend in Proportions data:? smokers out of patients , ?using scores: 1 2 3 4 X-squared = 8.2249, df = 1, p-value = 0.004132 How can one determine the direction of the trend? Thomas Subia [[alternative HTML version deleted]]