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Categorical Data Analysis Using The SAS® System, 2nd Edition by Gary G. Koch, Charles S. Davis, Maura E. Stokes

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9.2. Ordinal Response: Proportional Odds Model

9.2.1. Methodology

Consider the arthritis pain data in Table 9.1. Male and female subjects received an active or placebo treatment for their arthritis pain, and the subsequent extent of improvement was recorded as marked, some, or none (Koch and Edwards 1988).

Table 9.1. Arthritis Data
  Improvement 
SexTreatmentMarkedSomeNoneTotal
FemaleActive165627
FemalePlacebo671932
MaleActive52714
MalePlacebo101011

One possible analysis strategy is to create a dichotomous response variable by combining two of the response categories, basing a model on either Pr{marked improvement} versus Pr{some or no improvement} or Pr{marked or some improvement} versus Pr{no improvement}. However, since there is a natural ordering ...

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