Inferential Statistics Significance Testing Chapter 13 Important Terms

Important Terms • • • Null hypothesis Significance Probability of error (alpha levels) Confidence

Assumptions • Group studies – comparing experimental group with control group • Representative values

Comparing Mean Values • Mean values will be different • Caused by chance or

Null Hypothesis • Any observable difference between two mean values is simply due to

Calculation • Independent t-test • Non independent t-test • See p. 335

Independent t-test • To determine significance between two independent groups, i. e. , experimental

Significance • In essence, what is the likelihood that the group that receives the

Alpha Levels • The symbol p means probability of error • An alpha level

Alpha levels (cont. ) • An alpha level of. 01 means that less than

Non independent t-test • To determine significance between pre and post tests within one

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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