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Dependent Sample t-test
https://www.youtube.com/watch?v=zD3VIBkwc-0
Depicts the procedure to compute and apply t-statistic to test the difference across two dependent samples.  Special note: This video uses “before-after” when calculate the difference scores. Such an approach does not make any difference in a two-tailed test. However, it is better to use “after-before” to make sure the calculated differences are in the same direction as the alternative hypothesis.