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Inferential Statistics. Significance Testing Chapter 13. Important Terms. Null hypothesis Significance Probability of error (alpha levels) Confidence level Independent t test Dependent t test. Assumptions. Group studies – comparing experimental group with control group

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## Inferential Statistics

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**Inferential Statistics**Significance Testing Chapter 13**Important Terms**• Null hypothesis • Significance • Probability of error (alpha levels) • Confidence level • Independent t test • Dependent t test**Assumptions**• Group studies – comparing experimental group with control group • Representative values to describe performance in both groups – mean and Sd • Probability of replication**Comparing Mean Values**• Mean values will be different • Caused by chance or caused by IV**Null Hypothesis**• Any observable difference between two mean values is simply due to chance • Significance testing either accepts or rejects null hypothesis • Acceptance means that observable difference was due to chance • Rejection means the IV caused the change**Calculation**• Independent t-test • Non independent t-test • See p.335**Independent t-test**• To determine significance between two independent groups, i.e., experimental group and control group • Experimental group receives IV; control group does not • Was the difference between experimental group mean and control group great enough to state significance?**Significance**• In essence, what is the likelihood that the group that receives the IV will score higher than the group who does not? • In essence, what is the probability that the group who receives the IV will not score higher than the group who does not? • In essence, how confident are you that the group who receives the IV will score higher than the group who does not?**Alpha Levels**• The symbol p means probability of error • An alpha level of .05 means probability of error is less than 5 out of 100 times that the IV group might not score higher • Or, 95% of the times the IV group will score higher • See p. 329**Alpha levels (cont.)**• An alpha level of .01 means that less than 1 out of 100 times the IV group might not score higher • Or, 99% of the times the IV group will score higher • What about an alpha level of .001?**Non independent t-test**• To determine significance between pre and post tests within one group • One group, two treatments • Examples

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