Question 1:Using SPSS, compare the PEF measured using the two instruments using the paired t test. Report the results to a suitable number of decimal places.
Click Analyze, Compare Means, Paired-Samples T Test. Choose variables 'PEF (Wright meter)' and 'PEF (mini meter)'. Click OK.
You should get the following output:
| Paired Samples Statistics | |||||
|---|---|---|---|---|---|
| Mean | N | Std. Deviation | Std. Error Mean | ||
| Pair 1 | PEF (Wright meter) | 402.1667 | 12 | 94.97161 | 27.41594 |
| PEF (mini meter) | 419.3333 | 12 | 90.09624 | 26.00855 | |
| Paired Samples Correlations | ||||
|---|---|---|---|---|
| N | Correlation | Sig. | ||
| Pair 1 | PEF (Wright meter) & PEF (mini meter) | 12 | .906 | .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 | PEF (Wright meter) - PEF (mini meter) | -17.16667 | 40.32782 | 11.64164 | -42.78974 | 8.45641 | -1.475 | 11 | .168 |
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 = 0.168.
We should give the results to an appropriate number of decimal places. One decimal place looks about right. We could say that the mean difference, Wright minus mini, was −17.2 L/min, standard error = 11.6 L/min, 95% confidence interval = −42.8 to 8.5 L/min, P=0.2.
Back to Exercise: Comparing peak flow meters.
To Applied Biostatistics index.
To Martin Bland's M.Sc. index.
This page maintained by Martin Bland.
Last updated: 20 February, 2012.