Convergence Problems in Logistic Regression

A frequent problem in estimating logistic regression models is a failure of the likelihood maximization algorithm to converge. In most cases, this failure is a consequence of data patterns known as complete or quasi-complete separation. For these patterns, the maximum likelihood estimates simply do not exist. In this paper, I examine how and why complete or quasi-complete separation occur, and the effects they produce in output from SAS ® procedures.I then describe and evaluate several possible solutions.

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“…I also look at how several SAS procedures handle the problem. This paper is a revised and updated version of Allison (2004).…”

Section: Introductionmentioning

confidence: 99%

Predictors of outcome in civilian gunshot wounds to the head

Aarabi¹,

Tofighi

Kufera³

et al. 2014

JNS

103

112

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“…We considered the sample size of 90 border cells to be too small and therefore used a penalized maximum likelihood estimation. This method results in approximately unbiased estimates of coefficients even with small sample sizes and separation issues (Allison 2008;Firth 1993;Heinze and Schemper 2002). We built three separate models; the first model used all border crossing data by pooling both entry sites and exit sites, the second one used all entry crossings, and the third one used all exit crossings.…”

Section: Logistic Regression Models Using Penalized Maximum Likelihoomentioning

confidence: 99%

Understanding site selection of illegal border crossings into a fenced protected area: a rational choice approach

2018

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This study investigates illegal border crossings by rhino poachers into a fenced reserve in South Africa, comparing journeys to and after crime using a rational choice approach. Using various regression models, our analysis indicates poachers prefer to enter and exit the reserve near high rhino densities, while high road densities outside the reserve increase the odds of an illegal entry. The results also show that half of the incursions occurred at a single location, leading us to describe the special circumstances of this outlier. The study lays a foundation for understanding the location choices poachers make and presents a methodology that can be replicated in other reserves.

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“…In this study, blood type compatibility was not included in the multivariate analysis because complications occurred in all pa- Original Article tients with incompatible matching (16). However, blood type mismatch is thought to be a strong risk factor for severe complications, with 100% specificity (17).…”

Section: )mentioning

confidence: 99%