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Chapter 10: Analysis of Variance: Comparing More Than Two Means

Chapter 10: Analysis of Variance: Comparing More Than Two Means. Where We’ve Been. Presented methods for estimating and testing hypotheses about a single population mean Presented methods for comparing two population means. Where We’re Going.

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Chapter 10: Analysis of Variance: Comparing More Than Two Means

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  1. Chapter 10: Analysis of Variance: Comparing More Than Two Means

  2. Where We’ve Been • Presented methods for estimating and testing hypotheses about a single population mean • Presented methods for comparing two population means Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  3. Where We’re Going • Discuss the critical elements in the design of a sampling experiment • Investigate completely randomized, randomized block,and factorial designs • Show how to analyze data using a technique called analysis of variance Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  4. 10.1: Elements of a Designed Experiment Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  5. 10.1: Elements of a Designed Experiment Factor Levels are the values of the factors Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  6. 10.1: Elements of a Designed Experiment • Treatments are the factor-level combinations • In the example above, a variety of different GPA – Hours Studied combinations could occur within each subset (Yes or No) of the Study Group factor Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  7. 10.1: Elements of a Designed Experiment • An experimental unit is the object on which the response and factors are observed or measured • In the example above, an individual student would be the experimental unit Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  8. 10.1: Elements of a Designed Experiment Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  9. 10.1: Elements of a Designed Experiment The method by which the experimental units are selected determines the type of experiment Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  10. 10.1: Elements of a Designed Experiment Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  11. 10.2: The Completely Randomized Design The completely randomized design is a design in which treatments are randomly assigned to the experimental units or in which independent random samples of experimental units are selected for each treatment. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  12. 10.2: The Completely Randomized Design Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  13. 10.2: The Completely Randomized Design • Very often the object is to determine whether the varying treatments result in different means: H0: µ1 = µ2 = µ3 = µ4 = ···= µk Ha: At least two of the k treatment means differ Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  14. 10.2: The Completely Randomized Design • Testing the equity of the means involves comparing the variability among the different treatments as well as within the treatments, adjusted for degrees of freedom. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  15. 10.2: The Completely Randomized Design • Adjusting for degrees of freedom produces comparable measures of variability Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  16. 10.2: The Completely Randomized Design Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  17. 10.2: The Completely Randomized Design • The ratio of the variability among the treatment means to that within the treatment means is an F -statistic: with k-1 numerator and n-k denominator degrees of freedom. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  18. 10.2: The CompletelyRandomized Design If F* 1, the difference between the treatment means may be attributable to sampling error. If F* > 1 (significantly), there is support for the alternative hypothesis that the treatments themselves produce different results. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  19. 10.2: The CompletelyRandomized Design Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  20. 10.2: The CompletelyRandomized Design • Conditions required for a Valid ANOVA F-Test: Completely Randomized Design • The samples are randomly selected in an independent manner from the k treatment populations. • All k sampled populations have distributions that are approximately normal. • The k population variances are equal. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  21. 10.2: The Completely Randomized Design • The USGA compares the driving distance of four brands of golf balls. • H0: µ1 = µ2 = µ3 = µ4 • Ha: The mean distances differ for at least two of the brands •  = .10 • Test Statistic: F = MST/MSE • Rejection region: F > 2.25 = F.10 with v1= 3 and v2= 36 Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  22. 10.2: The Completely Randomized Design Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  23. 10.2: The Completely Randomized Design • The USGA compares the driving distance of four brands of golf balls. • H0: µ1 = µ2 = µ3 = µ4 • Ha: The mean distances differ for at least two of the brands •  = .10 Test Statistic: F = MST/MSE • Rejection region: F > 2.25 = F.10 with v1= 3 and v2= 36 Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  24. 10.2: The Completely Randomized Design • The USGA compares the driving distance of four brands of golf balls. • H0: µ1 = µ2 = µ3 = µ4 • Ha: The mean distances differ for at least two of the brands •  = .10 Test Statistic: F = MST/MSE • Rejection region: F > 2.25 = F.10 with v1= 3 and v2= 36 Since the calculated F > 2.25, we reject the null hypothesis. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  25. 10.2: The CompletelyRandomized Design • If the conditions for ANOVA are not met, a nonparametric procedure is recommended (see Chapter 14). • If the null hypothesis is not rejected, that is not conclusive proof that the treatment means are all equal. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  26. 10.3: Multiple Comparisons of Means • Suppose the ANOVA F-testindicates differences in the means. To determine the differences, we would compare the differences of the means. • With k treatment means, there are c = k(k – 1)/2 pairs of means to be compared, and each would have a significance level smaller than the overall . Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  27. 10.3: Multiple Comparisons of Means • To retain the overall confidence level, various techniques are available for pair wise comparisons: • Tukey – treatment sample sizes are equal • Bonferroni - treatment sample sizes may be unequal • Scheffé – general procedure for all linear combinations of treatment means Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  28. 10.3: Multiple Comparisons of Means • Let’s go back to the four brands of golf balls in the previous example: • Rank the treatment means with an overall 95% level of confidence using Tukey’s procedure. • Estimate the highest ranked golf ball's mean driving distance. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  29. 10.3: Multiple Comparisons of Means Pair wise Comparisons for Four Golf ball Brands Based on a SAS ANOVA report (see pages 506-7) Brand C outperforms each of the other brands. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  30. 10.3: Multiple Comparisons of Means • To construct a confidence interval on Brand C, we can use the descriptive statistics from the ANOVA and a straightforward one-sample t-based confidence interval (see section 7.3): Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  31. 10.4: The Randomized Block Design • The randomized block design: • Blocks (matched sets of experimental units) are formed. • Each of the b blocks has k experimental units, one for each treatment. • One experimental unit from each block is randomly assigned to each treatment, for a total of n = bk responses. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  32. 10.4: The Randomized Block Design • To test the equity of the means, we use the ratio MST/MSE ~ F Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  33. 10.4: The Randomized Block Design Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  34. 10.4: The Randomized Block Design Conditions required for a valid ANOVA F – Test • The b blocks are randomly selected and all k treatments are applied (in random order) to each block. • The distribution of observations corresponding to all bk block-treatment combinations are approximately normal. • The bk block-treatment distributions have equal variances. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  35. 10.4: The Randomized Block Design Completely Randomized Design Randomized Block Design Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  36. 10.4: The Randomized Block Design • Suppose the golf balls analyzed above are analyzed again using ten real golfers instead of a machine. • Each golfer is a block • Each brand is a treatment assigned in random order to each golfer • The ten drives for each brand produce the following means: Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  37. 10.4: The Randomized Block Design ANOVA Table for the Golf Ball Tests Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  38. 10.4: The Randomized Block Design Equity of Means 95% Confidence Intervals for the Golf Balls’ Distance None of the confidence intervals contain zero, so we can be 95% certain all of the brand means differ. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  39. 10.4: The Randomized Block Design ANOVA Table for the Golf Ball Tests To test for block mean differences, use the ratio of MSB to MEE Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  40. 10.5: Factorial Experiments • A complete factorial experiment is a factorial experiment in which every factor-level combination is utilized. That is, the number of treatments in the experiment equals the total number of factor-level combinations. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  41. 10.5: Factorial Experiments Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  42. 10.5: Factorial Experiments Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  43. 10.5: Factorial Experiments Stage 1 Stage 2 Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  44. 10.5: Factorial Experiments • Tests Conducted in Analyses of Factorial Experiments: Completely Randomized Design, r Replicates per Treatment Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  45. 10.5: Factorial Experiments • Tests Conducted in Analyses of Factorial Experiments: Completely Randomized Design, r Replicates per Treatment Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  46. 10.5: Factorial Experiments • Tests Conducted in Analyses of Factorial Experiments: Completely Randomized Design, r Replicates per Treatment Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  47. 10.5: Factorial Experiments • Tests Conducted in Analyses of Factorial Experiments: Completely Randomized Design, r Replicates per Treatment Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  48. 10.5: Factorial Experiments • Tests Conducted in Analyses of Factorial Experiments: Completely Randomized Design, r Replicates per Treatment • Conditions Required: • Response distribution for each factor-level combination is normal. • Response variance is constant for all treatments. • Random and independent samples of experimental units are associated with each treatment. Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  49. 10.5: Factorial Experiments • The four brands of golf balls are tested again, this time with a driver and a 5 iron. Each brand-club combination (eight in all) is assigned randomly to four experimental units in a sequence of swings by Iron Byron. • Are the treatment means equal? • Do the factors “brand“ and “club” interact? Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

  50. 10.5: Factorial Experiments TABLE 10.13: ANOVA Summary Table for Example 10.10 Statistics for Business and Economics, 11th ed. Chapter 10: Analysis of Variance

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