Categorical Data Analysis Using The SAS® System, 2nd Edition

10.8. Exact Conditional Logistic Regression in the Stratified Setting

While conditional logistic regression often serves to counterbalance the small counts in a strata by conditioning away the strata effect, sometimes the data are so sparse that these methods also become inappropriate. The conditional exact inference described in Chapter 8 also applies to the stratified setting. Note that in the asymptotic logistic regression setting, the methodology for the unstratified and stratified analysis is different (the former is based on an unconditional likelihood and the latter is based on a conditional likelihood). In the exact setting, you use the same methodology (involving conditioning). The only difference is that, in the unstratified case, ...