29.5 P-values: Mean differences

A P-value determines if the sample data are consistent with the assumption (Table 28.1), Since t=1.681, the one-tailed P-value is between 2.5% and 16% based on the 68–95–99.7 rule. This is a wide, and inconclusive, interval. Software gives a more precise P-value (jamovi: Fig. 29.4; SPSS: Fig. 29.5): the two-tailed P-value is 0.127, so the one-tailed P-value is 0.127/2=0.0635.

jamovi output for the insulation data

FIGURE 29.4: jamovi output for the insulation data

SPSS output for the insulation data

FIGURE 29.5: SPSS output for the insulation data

The software clarifies how the differences have been computed:

  • jamovi: At the left of the output (Fig. 29.4), the order implies the differences are found as Before minus After.

  • SPSS: At the left of the output (Fig. 29.5), the difference is described as Before After.

Click on the hotspots in the following image, to see how to read the SPSS output.