There are two types of t tests: equal variances and unequal variances.
• If you select the Means/Anova/Pooled t option, a Pooled t Test report appears. This t test assumes equal variances.
• If you select the t Test option from the red triangle menu, a t test report appears. This t test assumes unequal variances.
The t Test report contains the following columns:
t Test plot
Shows the sampling distribution of the difference in the means, assuming that the null hypothesis is true. The vertical red line is the actual difference in the means. The shaded areas correspond to the p-values.
Difference
Shows the estimated difference between the two X levels. In the plots, the Difference value appears as a red line that compares the two levels.
Std Err Dif
Shows the standard error of the difference.
Upper CL Dif
Shows the upper confidence limit for the difference.
Lower CL Dif
Shows the lower confidence limit for the difference.
Confidence
Shows the level of confidence (1-alpha). To change the level of confidence, select a new alpha level from the Set α Level command from the platform red triangle menu.
t Ratio
Value of the t-statistic.
DF
The degrees of freedom used in the t test.
Prob > |t|
The p-value associated with a two-tailed test.
Prob > t
The p-value associated with an upper-tailed test.
Prob < t
The p-value associated with a lower-tailed test.