Useful when: you have two sets of measurements, and want to know if there has been a shift in mean value.
Use Student’s t-test for significantly different means.
Sample variance for sample A:
Similarly for sample B. Then
Finding the significance level
Use the t-distribution with degrees of freedom to compute the significance level, which is the probability that could be larger, by chance, for distributions of equal means. Thus a significance of 0.05 suggests that the means are different with 95% confidence.
Testing against a significance level
For e.g. a test with 95% confidence level, find the threshold value of t at 0.05 from the t-distribution. If the computed t exceeds the threshold, the means are considered different to that level of confidence.
Octave – t_test
Perl – Statistics::TTest
Spreadsheet – TTEST, TDIST, TINV