Question: Three drug treatments are compared at three sites. The treatments consist of two dosages (low and high dose) of an experimental drug and a control drug. The results were analysed by two-way ANOVA with interaction. The ANOVA is shown below.

Analysis of Variance for response

Source DF SS MS F P

site 2 21.301 10.651 0.47 0.656

dose 2 185.404 92.702 4.09 0.108

site*dose 4 90.654 22.663 7.05 0.000

Error 63 202.574 3.215

Total 71 499.933

(i) What was the level of replication? How do you know?

(ii) State all the hypotheses that may be tested. Test each hypothesis working in the correct order and state your conclusions.

(iii) Distinguish between an interaction and a main effect, in this experiment.