a group of 1,000 randomly selected adults is classified into 4 smoking groups: nonsmoker, light smoker, moderate smoker, and heavy smoker. at the end of a ten-year period, the proportion in each group who developed lung cancer was determined. the null hypothesis is that all 4 groups will have the same incidence rate of lung cancer. the p-value is found to be smaller than the level of significance (i.e. smaller than .05). what is the most appropriate conclusion?