Suggested answer to exercise: Comparing peak flow meters, 1

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.

Suggested answer

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.

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Last updated: 20 February, 2012.

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