First select the variables for sample 1 and sample 2, and a possible selection criterion for the data pairs.  

Use the 

 button to select variables and selection criteria in the variables list.   

Options 

Logarithmic transformation: select this option if the data are positively skewed. 

Results 

The program displays the summary statistics of the two samples followed by the mean of the differences 

between the paired observations, and the standard deviation of these differences, followed by a 95% 

confidence interval for the mean. 

Note that the sample size will always be equal (only cases are included with data available for the two 

variables).  

Next the result of the null hypothesis test is displayed.  If the calculated P value is less than 0.05, the 

conclusion is that the mean difference between the paired observations is statistically significantly different 

from 0. 

Log transformation 

If you selected the Log transformation option, the program performs the calculations on the logarithms of 

the observations, but reports the back transformed summary statistics.   

For the paired t test, the mean difference and 95% confidence are given on the log transformed scale. 

Next, the results of the t test are transformed back and the interpretation is as follows: the back 

transformed mean difference of the logs is the geometric mean of the ratio of paired values on the original 

scale (see Altman, 1991). 

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