Which Test to Use?Intro to t-tests & chi-squareDecision Tree(cont.)T-test v Z-testTypes of T-testsExamples of t-testsLab 19Which Test to Use?Wed, March 31stIntro to t-tests & chi-squareNext few weeks, will discuss 3 different types of t-tests & chi-squareHow to decide when to use each test:–Use Decision tree link for today–Consider design of the study:–Examining differences or relationships?–# samples or groups (1 or 2)?–If more than 1 group, were they matched?–If only 1 group, how many scores from subjects?Decision TreeWe have already covered correlation & regression, chi-sq is a similar option:–Use corr or chi-sq when interested in whether there is a relationship betw 2 variables–Correlation – relationship betw two interval/ratio variables·is age related to hours of sleep per night?(cont.)–Chi-square – relationship betw two nominal/ordinal variables·Is gender related to preference for Kerry v Bush? (Lab 24, 4/19)T-test v Z-testWe’ve also already covered the z test–Use to compare a sample & pop mean when pop standard dev () is knownZ test is similar to a 1-sample t-test–1-sample t test compares a sample & pop mean, but pop standard dev () is unknown–Will cover 1-sample t in Lab 20 (Apr 5th)Types of T-testsBesides 1-sample t-test, there are 2 other types:–Independent Samples t-test: use when comparing sample means of 2 unrelated (indep) samples–Related Samples t-test: 2 options·Repeated Measures: compare 1 samples’ means at 2 different times·Matched Pairs – Pairs are created & 1 person is put in 1st group; 2nd person put in 2nd group  compare means of Group 1 and Group 2.Examples of t-testsInd Samples: compare men and women’s mean job stress scores (Lab 22, 4/12)Related Samples (Repeated Measures): compare mean scores of 50 students at pre-test v. post-test (Lab 21, 4/7)–(note: 1 sample, but measured twice)Related Samples (Matched Pairs): Pairs of twins – randomly assign Twin 1 to a group, Twin 2 to the other group & compare group means (Lab 21, 4/7)–(note: 2 groups, but they aren’t independent, they’re related)Lab 19Notice 1 branch of decision tree includes comparisons among more than 2 groups–This is beyond 138 material, but may be an answer to one of the lab scenarios (just indicate ‘beyond 138’!)Also indicate for ea. Question, 1 or 2-tailed test? Read the Ha – if specifies a direction  1-tailed; if simply “not equal to…” or no difference  2-tailedSkip