4.26* The data below are taken from Pierce et al. (1979), and summarise the daily mortality in groups of fish subjected to three levels of zinc concentration. Half the fish at each concentration level received one week’s acclimatisation to the test aquaria, and half received two weeks’ acclimatisation.

There were therefore six treatment groups, and 50 fish were randomised to each group, resulting in 300 fish in total in the experiment.