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Section 13.2 Chi-square Test of Association / Independence

Section 13.2 Chi-square Test of Association / Independence. AP Statistics March 30, 2010 Berkley High School. Housekeeping. Χ 2 with df=10 can be expressed using the shorthand notation: Χ 2 (10) The answer to question 4 on the sample test is wrong ; the correct answer is C . . Example.

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Section 13.2 Chi-square Test of Association / Independence

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  1. Section 13.2Chi-square Test of Association / Independence AP Statistics March 30, 2010 Berkley High School

  2. Housekeeping • Χ2 with df=10 can be expressed using the shorthand notation: Χ2(10) • The answer to question 4 on the sample test is wrong; the correct answer is C. AP Statistics, Section 13.1

  3. Example • Chronic users of cocaine need the drug to feel pleasure. Perhaps giving them a medication that fights depression will help them stay off cocaine. A three-year study compared an antidepressant call desipramine with lithium (a standard treatment for cocaine addiction) and a placebo. • The subjects were 72 chronic users of cocaine who wanted to break their addiction. AP Statistics, Section 13.1

  4. Observed AP Statistics, Section 13.1

  5. Expected (assuming independence) AP Statistics, Section 13.1

  6. Formula for expected counts AP Statistics, Section 13.1

  7. AP Statistics, Section 13.1

  8. AP Statistics, Section 13.1

  9. What new for Chi-squared Test for independence • H0: the categories are independent. • Ha: the categories are not independent. • You can safely use the chi-square test with critical values from the chi-square distribution when no more than 20% of the expected counts are less than 5 and all individual expected counts are 1 or greater. In particular, all four expected counts in a 2X2 table should be 5 or greater. AP Statistics, Section 13.1

  10. On the calculator • The “observed” data goes into matrix, typically, A • Run the χ2-Test from the Stats:Test • You specify where you want the expected matrix to go. AP Statistics, Section 13.1

  11. Exercises • 13.15-13.29 odd • Chapter Review: 13.31-39 odd AP Statistics, Section 13.1

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