Compare means in two dependent groups

To compare the means in two dependent groups, the t-test for dependent groups can be used. In this example, a dataset/dataframe called dat contains two continuous variables called dependentVariable_t0 and dependentVariable_t1

SPSS

T-TEST PAIRS = dependentVariable_t0 WITH
               dependentVariable_t1 (PAIRED).

R

meanDiff(dependentVariable_t0, dependentVariable_t1,
         paired=TRUE);