Hi all, The "meantest" command provides a simple way to conduct a paired t-test comparing the mean values between TWO series. The help says: """ Paired test In the primary case (only) the --⁠paired option can be given, to test the null hypothesis that the mean difference between the paired values of the two series arguments is zero. Otherwise, pairing is not assumed. """ Take the following example which I would expect to fail as only a single series is provided: <hansl> open mrw --quiet summary gdpgrow --simple meantest gdpgrow --paired </> However, the output is: """ Summary statistics, using the observations 1 - 121 for the variable 'gdpgrow' (117 valid observations) Mean 4.09402 Minimum -0.900000 Maximum 9.20000 Standard deviation 1.89146 Missing obs. 4 Paired difference test Number of observations = 117 Sample mean paired difference = 3.09402 Null hypothesis: The population mean difference is zero. Estimated standard error = 0.174866 Test statistic: t(116) = 17.6937 p-value (two-tailed) = 9.72895e-35 """ It looks as in case no 2nd series is provided, the test compares to a constant series - compare with this: <hansl> # Compare series y = 1 meantest gdpgrow y --paired </> I guess that should be mentioned in the help text or output. Alternatively, an error may be flagged as two series are expected. Best Artur