09 Inferential Statistics, External Validity

09 Inferential Statistics, External Validity - 1...

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11/9/2016 1 INFERENTIAL STATISTICS EXTERNAL VALIDITY Class 9 Announcement LECTURE OUTLINE Inferential Statistics Error Null hypothesis t test F test External Validity Exact Replication Conceptual Replication Meta-analysis INFERENTIAL STATISTICS Learning by disconfirming INFERENTIAL STATISTICS We can tell Main effects 1 2 3 4 5

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11/9/2016 2 Interactions These suggest that IVs affect the DV A causal relationship One main effect per factor or variable! FAIL? The results that we obtained could be WRONG. Sampling Participant variability Experimenter bias Convenience/Haphazard sampling Testing Experimenter bias Flaws in design Reactivity PROBLEMS Sampling Most Universities use Haphazard Sampling!! Finding truly representative samples is very difficult generalizability PROBLEMS If we study university undergrads, how do the results compare to another group of people (senior citizens, for example)? 6 7 8
11/9/2016 3 Do measures of religiosity in a Christian college reflect what all students think? Do measures of play behavior in upper-middle class children compare to working class children? Does measuring the attention span of inmates in one prison compare to the attention spans of inmates in another? MO’ PROBLEMS Reliability Scientists make mistakes in measuring Validity Scientists make mistakes in experimental design MO’ PROBLEMS Scientists combine all forms of mistakes Confounding variables Unknown variables Randomness Error ERROR A measure of any variability in all of the variables in an experiment that are NOT controlled, randomized, or manipulated. 9 10 11

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11/9/2016 4 ERROR Cannot know absolute truths What we know is relative to other things Scientist CANNOT and WILL NOT prove absolute truth The DV is affected by so many things OTHER than the IV. Alternative Explanations Effects of error The effects of manipulations MUST be stronger than the effects of error. HOW WE ROLL Scientists always disconfirm. Never confirm. Therefore, we use error to our advantage Null Hypothesis (H 0 ) Research Hypothesis (H 1 ) “Alternate Hypothesis” (H A ) “Hypothesis” NULL HYPOTHESIS The antithesis of the research hypothesis. It is the hypothesis that the manipulation of the IV has no effect on changes in the DV.
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