Question 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, which gave P = 0.0063?
Click Analyze, Compare Means, Paired-Samples T Test. Choose variables 'Attacks while on placebo' and 'Attacks while on pronethalol'. Click OK.
You should get the following output:
| Paired Samples Statistics | |||||
|---|---|---|---|---|---|
| Mean | N | Std. Deviation | Std. Error Mean | ||
| Pair 1 | Attacks while on placebo | 53.42 | 12 | 89.069 | 25.712 |
| Attacks while on pronethalol | 45.75 | 12 | 97.185 | 28.055 | |
| Paired Samples Correlations | ||||
|---|---|---|---|---|
| N | Correlation | Sig. | ||
| Pair 1 | Attacks while on placebo & Attacks while on pronethalol | 12 | .991 | .000 |
| Paired Samples Test | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Paired Differences | t | df | Sig. (2-tailed) | ||||||
| Mean | Std. Deviation | Std. Error Mean | 95% Confidence Interval of the Difference | ||||||
| Lower | Upper | ||||||||
| Pair 1 | Attacks while on placebo - Attacks while on pronethalol | 7.667 | 15.108 | 4.361 | -1.932 | 17.266 | 1.758 | 11 | .107 |
The first table shows the two variables separately. The second table shows something about the relationship between the two variables, which we shall cover in Week 8. The third table shows the results of the t test and we have P = 0.107.
The P value is considerably larger than the 0.0063 for the sign test and is not significant.
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Last updated: 20 February, 2012.