Paired t

Test of the Differences - Confidence Interval

  

The confidence interval is a range of likely values for m D. Since you do not know the true value of m D, the confidence interval allows you to guess its value based on the sample data. The mean sample difference provides an estimate of m D, and the standard deviation (StDev) of the sample difference is used to determine how far off the estimate might be. In general, the proportion of intervals that include m D is equal to 1 minus the chosen a-level. You can choose any a-level that is greater than 0% and less than 100%. The 0.05 a-level is commonly used.

 

Example Output

Paired T for Before - After

 

             N    Mean  StDev  SE Mean

Before      15  74.667  3.478    0.898

After       15  72.333  3.200    0.826

Difference  15   2.333  3.352    0.866

 

 

95% CI for mean difference: (0.477, 4.190)

T-Test of mean difference = 0 (vs ≠ 0): T-Value = 2.70  P-Value = 0.017

Interpretation

Since the heart rate data were analyzed with an a-level of 0.05, a 95% (or 0.95) confidence interval was constructed. This interval tells you that, based on the sample data, you can be 95% confident that m D is greater than or equal to 0.477 and less than or equal to 4.190.

Since the reference value of 0 is not within the confidence interval, you can reject H0 with 95% confidence and conclude that m D is not 0.