# PSY 303 Lecture 16: 303 Contrasts

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8 Feb 2017
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Psych 303
2/8/17
Contrasts
A. Problem set due Friday (still)
B. Finalize materials section
C. Sigle page of materials
D. Contrast- an analysis of a specific variance
- Portion of BGV accounted for by a specific predicted pattern of means
- The obtained means are weighted based on what was predicted
- To the extent that the obtained patterns of means corresponds to the predicted
pattern, the contrast will be stronger
- The contrast SS will be a greater proportion of BGV
E. ANOVA source tablecontrasts are part of between group-variance.
F. Spss gives contrasts in form of T-Test.
G. Where contrasts fall short
- Predicted meansex: blue ink increases self esttem relative to red and black ink
(Hypothesis) \red ink and black ink vs blue ink
- Actual means -red=4.3, black=6.0, blye-6.2
- (-1)4.3+(-1)6.02(6.2)
- =-4.3+-6.0+12.4=2.1
- SSt=5.88
- F(1, 21)= 5.88/.225= p<.001 stat sig ---in a way---does’t eessarily fit data
- This situation would make sense to do a post hoc test
- Contrast test based on specified pattern of weights may yield s dignificant contrast F
- But actual means may be inconsistent with weights!
predicted means:
- Red ink lowers SE compared to black or blue ink
- Red ink vs black ink+ blue ink
- Still have to look at hypothesisdo they correspond to the weights you used?
H. Contrast Weights
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