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Analysis of Treatment Means. KNNL – Chapter 17. Cell Means Model – Sampling Distributions and Graphs. Inference for Individual Treatment Means. Comparing Two Treatment Means. Contrasts among Treatment Means. Simultaneous Comparisons.
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Analysis of Treatment Means KNNL – Chapter 17
Simultaneous Comparisons • Confidence Coefficient (1-a) applies to only one estimate or comparison, not several comparisons simultaneously. Confidence Coefficient for a “family” of tests/intervals will be smaller than confidence coefficient for “individual” tests/intervals • If we construct five independent confidence intervals, each with confidence level = 0.95, Pr{All Correct} = (0.95)5 = 0.774 • Confidence Coefficient (1-a) applies to only pre-planned comparisons, not those suggested by observed samples (referred to as “data snooping”). • If we wait until after observing the data, then decide to test whether most extreme means are different, actual a too high
SNK Method for All Pairwise Comparisons • Controls False Discovery Rate at e • Uses Different Critical Values for different ranges of means
Duncan’s Method for All Pairwise Comparisons • More powerful than SNK method, at cost of increasing e for longer stretches (does not control experimentwise error rate) • Uses Different Critical Values for different ranges of means