Week 7 CI_t test_rev 3_7_09

Week 7 CI_t test_rev 3_7_09 - SAN JOS STATE UNIVERSITY...

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SAN JOSÉ STATE UNIVERSITY College of Social Work S. W. 242 Spring 2009 Edward Cohen Next week: *Meet at lab classroom for t -test lab assignments (#2a and 2b) *We’ll review material for exam, then distribute take home exam *Introduction to ANOVA Week 7: March 6, 2008 Confidence Intervals Lab #1 (Chi-square) Comparing means of two groups: t -tests Final Paper preparation Take home exam due at beginning of class March 13 Concepts you should know: H O -- The null hypothesis H A -- The alternative hypothesis Confidence interval of the mean Standard error of the mean Dichotomous variable Assumptions for using t -test Equality of variances Independent groups t -test Dependent group (or paired sample) t -test Degrees of freedom (and the t -test) Confidence interval of the difference between means I. Review: If… The independent variable is : And the dependent variable is: Then the statistical test is: Categorical Categorical Chi square Nominal (dichotomous) Continuous t - test II. t –test: comparing means of 2 groups; independent variable is nominal (dichotomous—the 2 groups), and dependent variable is continuous Two types: Independent groups t -test Dependent groups (or paired samples) t -test A. Independent sample t -test Comparing the means of two independently chosen samples Example: H A : SJSU students receiving post-grad test preparation will score higher in the LCSW exam compared to those SJSU students who did not receive post-grad test preparation Eight steps to testing hypothesis:
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1. What is the independent variable, and its level of measurement? Group (test prep vs. no test prep); nominal (dichotomous) 2. What is the dependent variable , and its level of measurement? LCSW test score; continuous 3. What’s the Null Hypothesis? There is no difference in LCSW test scores between the two groups. 4. Is the alternative hypothesis stated above one-tailed or two-tailed? There is a difference in the test scores between the two groups (two-tailed); OR, The group receiving test preparation will score higher in the LCSW exam than the group not receiving test prep (one-tailed) 5. Statistical test & alpha level: Independent sample t -test, alpha < .05 6. Review SPSS table of results 7. Describe results & decision to accept or reject Null –using standard reporting of statistic: ( t = __, df = ___, p = ___) 8. Discuss results B. Dependent (or Paired) sample t –test Comparing the means of two related samples, or more typically, the same sample measured twice Example: H A : LCSW test preparation will result in reduced anxiety as measured by a ratio level anxiety scale score, comparing scores pre- and post- test preparation Eight steps to testing hypothesis: 1. What is the independent variable, and its level of measurement? One group (pretest, posttest) 2. What is the dependent variable , and its level of measurement? Anxiety scale score; continuous 3. What’s the Null Hypothesis? There is no difference in pretest and posttest anxiety scale scores.
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This note was uploaded on 09/08/2010 for the course SCWK 298 at San Jose State University .

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Week 7 CI_t test_rev 3_7_09 - SAN JOS STATE UNIVERSITY...

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