tailieunhanh - Engineering Statistics Handbook Episode 9 Part 15

Tham khảo tài liệu 'engineering statistics handbook episode 9 part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | . How can we make multiple comparisons ANOVA F test is a preliminary test Procedures for examining factor-level effects Determine contrasts in advance of observing the experimental results The ANOVA uses the F test to determine whether there exists a significant difference among treatment means or interactions. In this sense it is a preliminary test that informs us if we should continue the investigation of the data at hand. If the null hypothesis no difference among treatments or interactions is accepted there is an implication that no relation exists between the factor levels and the response. There is not much we can learn and we are finished with the analysis. When the F test rejects the null hypothesis we usually want to undertake a thorough analysis of the nature of the factor-level effects. Previously we discussed several procedures for examining particular factor-level effects. These were Estimation of the Difference Between Two Factor Means Estimation of Factor Level Effects Confidence Intervals For A Contrast These types of investigations should be done on combinations of factors that were determined in advance of observing the experimental results or else the confidence levels are not as specified by the procedure. Also doing several comparisons might change the overall confidence level see note above . This can be avoided by carefully selecting contrasts to investigate in advance and making sure that the number of such contrasts does not exceed the number of degrees of freedom between the treatments only orthogonal contrasts are chosen. However there are also several powerful multiple comparison procedures we can use after observing the experimental results. Tests on Means after Experimentation http div898 handbook prc section4 2 of 3 5 1 2006 10 39 06 AM . How can we make multiple comparisons Procedures If the decision on what comparisons to make is withheld until after the for data are examined the following .