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Unformatted text preview: Notes on week 6 material Notices • Midterm 2 next Wednesday during class • Study guide is posted • Do the homework problems from chs 10 & 12 – No real computation, very much like stuff that will be on the test • Change in my office hours for next week – Tuesday 24 in FH 6625 – No OH on Wednesday (no point) • No discussion next week (no point) What you should know • Ztest • Ttests – Single sample vs independent groups vs within groups • One factor ANOVAs – Between subjects/Independent groups – Within subjects/Repeated measures • When to use these things, how to evaluate them, and what they mean • Post hoc tests • Effect size Review: Variables • Independent variable (IV) – What the experimenter manipulated – Often called “Factor” – Can have multiple levels (e.g., conditions) • Dependent variable (DV) – What the experimenter measured Ttest leftovers Independent samples ttest • Two different groups – Different people in each group • No information about the population is given to you • Numerator: difference between group means = X A1 X A2 Independent samples ttest • Two different groups – Different people in each group • No information about the population is given to you • Denominator: standard error based on sampling distribution of difference between means = s XA1  XA2 This is one standard error, NOT the standard error of A1 minus the standard error of A2 Independent samples ttest • The formula t obs = X A1 X A2 s XA1  XA2 Denominator is the standard error of the difference between means This is the standard deviation of the sampling distribution of differences between means (i.e., it is a standard error) Standard error in independent samples ttest • Standard deviation of sampling distribution of differences between means • Since σ is not known, sample values must be used • Leads to a big messy formula s XA1  XA2 = ( n A11)s 2 A1 + ( n A21)s 2 A2 1 1 n A1 + n A2 2 n A1 n A2 + Standard error in independent samples ttest s XA1  XA2 = ( n A11)s 2 A1 + ( n A21)s 2 A2 1 1 n A1 + n A2 2 n A1 n A2 + This part is the pooled variance It takes into account the variance and sample size of each sample Standard error in independent samples ttest s XA1  XA2 = ( n A11)s 2 A1 + ( n A21)s 2 A2 1 1 n A1 + n A2 2 n A1 n A2 + Considering that s X can be rewritten as (s 2 )(1/N) You should be able to see how the formula below is a standard error Independent samples ttest • You will not need to memorize the formula for the test • You should know what the numerator and denominator are (conceptually) • You should know how to conduct and evaluate the test – Given the standard error, critical values, alpha level, # tails, etc. Independent samples ttest • How to evaluate • Compare t obt to t crit – Must know N ( df ), alphalevel, #tails to find t crit • df = N  2 = n A1 + n A2 2 – bc there are two groups • If t obt exceeds t crit , reject null hypothesis Repeated measures ttest...
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 Winter '07
 Marken
 Statistics, Normal Distribution, Independent Samples tTest

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