# Exercise: Normal plot for angina and pronethalol

The file angina.sav contains the data from the pronethalol for angina crossover trial analysed in the lecture for Week 4.

## Questions

1. Using SPSS, compare the numbers of attacks on the two drug treatments using the paired t test. How does the result compare with that from the sign test in Week 4?

2. Compute the differences in number of attacks, placebo minus pronethalol, and draw a Normal plot (Q-Q plot). Does the distribution look Normal?

3. Compute the average number of attacks on placebo adnd pronethalol and draw a scatter plot of difference against average. Do the differences and averages of the numbers of attacks appear to be related?

5. If the data do not meet the assumptions of a t test, we may find a mathematical transformation of the data which will do so. We shall try the square root. Compute the difference between the square root of the number of attacks on placebo and the number of attacks on pronethalol and draw a Normal plot.

6. Compute the average of the square roots of the number of attacks on placebo adnd pronethalol and draw a scatter plot of difference against average. Do the difference and average after square root transformation appear to be related?

7. Do you think the square root transformed data meet the conditions for a paired t test? Are they closer than are the raw data?

8. Compare the square root transformed numbers of attacks on the two drug treatments using the paired t test. How does the result compare with those from the sign test and from the t test on the raw data?