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Unformatted text preview: seline category (i.e. women
with no laceration). DISCUSSION
Choice of an Ordinal Model
The choice between the cumulative logit and
continuation-ratio models merit further discussion.
Armstrong and Sloan15 argue that when the cumulative
logit model is valid implying that the cumulative logodds ratios are a constant, say β*, then the continuationratio model will begin at βj = β*, but will approach 0 as
j increases. This argument has led to the cumulative
logit model being proposed as an adjunct to the Cox’s
proportional hazards model13 i.e. continuation-ratio
model for survival data when hazard rates of groups are
thought likely to converge with time (see McCullagh4
and McCullagh and Nelder14 for a more thorough
The choice of a simple logistic model to an ordered
response has its own disadvantages. Based on extensive
simulations, Armstrong and Sloan15 conclude that the
logistic model attains only between 50 and 75% efficiency, relative to the cumulative logit model for a fivelevel ordered response. Moreover, efficiency...
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- Spring '11