1. Dependent t-test

2. Varieties of t 1-Sample (only one kind) 2-Sample (two kinds)
Independent samples – groups are unrelated
Experimental vs. control groups (at random)
Male vs. female participants (unrelated)
Dependent samples – groups are related
Same person in both groups
Left hand vs. right hand
Pain-free vs. placebo
Groups are related somehow
Wife, husband
Cancer patient, friend

3. Dependent t Formulas
Observations come in pairs. Brother, sister, repeated measure.
Dependent t is equivalent to a single sample t computed on differences.
Problem solved by finding diffs between pairs Di=Xi1-Xi2.
df=N(pairs)-1

4. Dependent t Example
Brother (X1)
Sister(X2) 5 7 8 3
Diff 2 1

5. Six Steps 1. Alpha = .05 2. Null & Alt: 3. Calc stat:
4. Crit value: df = N-1 =2, alpha .05, 2 tails.
5. Decision rule:
6. Conclusion:
t = 4.30
Reject if |tobt| > tcrit
N.S., i.e., no difference.

6. Faces – how attractive are they?B
Rate each face on a scale from 1 to 10 where 1 is unattractive and 10 is extremely attractive.