The Student 't' Calculation -- Comparing Two Groups
These figures are from
Q - Approach to Quality
© 1998 by Jay Warner. Reproduction rights reserved.
Students, and working people(!), often get confused by when they need to compare two groups of data rigorously. Yet we need to make decisions with confidence that the measurements back us up -- should the production machine be adjusted; did the marketing video really improve sales? There are so many versions of the Student 't' equation, all closely related. Which fits your situation? Follow the steps, weave through the Guide Sheet below. You'll get to the right place!
Question: Is there a difference (between two groups)?
When comparing two groups using internal estimates of both s, use s1 = s2 branch when (a) n1 is approximately equal to n2,
, (b) F-ratio <2.5
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