1. T-TEST FOR CORRELATIVEGROUPS
- Usedto compare twogroupswhose measurementsare interval orration,where the
samplesare observedbefore andafterthe introductionof the independentvariable
- Usedin:
 Pre-testandpost-testof samples
 Repeatedmeasures withinsubjectdesigns
 Matched sample designs
* two-tailedtestof significance isused( ±)
*assume normal distribution
How to use:
1. State hypotheses.
Ho (null hypothesis) : Ma = Mb
Ha (alternative hypothesis):Ma= Mb
2. Findthe critical areaor t critical.
a. State 𝛼, or the level of significance.
b. Finddf,where df=n -1, where n= numberof samples  n-1 because onlyone groupof
samplesisused
c. Look upthe critical/tabularvalue of ton the table.
3. Set upthis table:
Sample/s Numerical
measurement
before
manipulation
Numerical
measurement
aftermanipulation
D D2
Where:
D = measurementsbefore –measurementsafter * noabsolute value
𝐷2 = (measurements before – measurements after)2
4. Calculate forthe test statistic,ort calc
a. Calculate the sumof squaresof the difference score,or ∑ 𝑑²
∑𝑑² = ∑ 𝐷² −
(∑ 𝐷)²
𝑛
 n = numberof samples
b. Calculate the standarderrorof meandifference,or 𝑆 𝐷
𝑆 𝐷 = √
∑ 𝑑²
𝑛(𝑛 − 1)

2. c. Calculate 𝐷
𝐷 =
∑ 𝐷
𝑛
d.Calculate t
𝑡 =
𝐷
𝑆 𝐷
* the final value of tmust be ±, since it’sa two-tailedtest.
5. Formulate the conclusion.
If:t calc > t critical
acceptHa, rejectHo the manipulationhasa significanteffect.
If:t calc < t critical
acceptHo, rejectHa  the manipulationhasnosignificanteffect.