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Unformatted text preview: onstraints specified a priori: 1 = 0, 2 = 1, 3 = 2, and
4 = 7. These resulted in the following log-ratios: β,
β + γ , β + 2 γ , and β + 7 γ , for the four logits, as
described earlier. Our choice of constraints were based
on examining the log odds ratios from the observed data,
which were derived by constructing four 2 × 2 tables,
with episiotomy (yes/no) as the two rows, and lacerations ‘any’ versus ‘none’ as the columns for the first
table; 2° – 4° versus none plus 1° for the second table,
and so on. A simultaneous test of H0: β = 0, γ = 0
(based on 2 d.f.) resulted in a χ2 = 85.6, implying good
fit. Notice that the choice of different constraints will
produce different parameter estimates and standard
The results of fitting the polytomous logistic and the
adjacent-category logistic models are summarized in
Table 6. The formulation of these models is more
flexible when compared to the proportional odds and
continuation-ratio models, in that the regression coe...
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This document was uploaded on 02/25/2014.
- Spring '11