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Results tagged with separation
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user 11887
Separation occurs when some classes of a categorical outcome can be perfectly distinguished by a linear combination of other variables.
2
votes
Complete separation in logistic regression with only one direction
The paper you linked do not have a correct definition of complete separation, it says that only occurs if it is caused by one variable $s_i$. … That is not correct, complete separation can well occur without any single variable causing it. …
- 82.8k
1
vote
likelihood ratio test for logistic regression with a complete separation
You can still use the likelihood ratio test with separation. … For more details on logistic regression and separation see How to deal with perfect separation in logistic regression? and GLM high standard errors, but variables are definitely not collinear. …
- 82.8k
5
votes
Why is it desirable to have linear separability in SVM?
In the example you show, point lie on concentric annular rings, which cannot be separated by any plane, but by introducing a new variable RADIUS---distance from center---you get complete linear separation …
- 82.8k
4
votes
Normally distributed estimated parameters in logistic regression
Well, you can define the $Z$ statistic by the same formulas (well, actually using asymptotic approximations) that is used in the normal case. There is no implication that the resulting statistic do h …
- 82.8k
2
votes
instability of logistic regression
Well, if your goal is discrimination, it doesn't really matter if the estimated parameters are unstable---the class assignments could well be stable! Even, if your goal is risk estimation, even if the …
- 82.8k
0
votes
any problems with Firths Logit model (to deal with separation)
Partially answered in comments:
No time to provide an elaborate response, but Greenland recommends log-F(1,1) prior instead of Firth's bias correction method. And you can implement it by simply modif …
45
votes
Why does logistic regression become unstable when classes are well-separated?
(y ~ x, family=binomial, separation="test")
Error in glm(y ~ x, family = binomial, separation = "test") :
Separation exists among the sample points. … =binomial, separation="test")
Error in glm(y ~ x, family = binomial, separation = "test") :
Separation exists among the sample points. …
- 82.8k
1
vote
Perfect separation error message for glm with binomial but not with quasibinomial family
for some ideas of what to do in this case of separation. …
- 82.8k
1
vote
Dealing with quasi-complete separation in General Additive Model?
Your diagnosis is probably correct, and the big standard errors is because the loglikelihood function in this case is far from quadratic. Confidence intervals based on likelihood profiling might be be …
- 82.8k
4
votes
If logistic regression is a linear classifier why does it fail on linearly separable data?
If the data are linearly separable with a positive margin, so that it can be separated by a plane in more than two (so infinitely many ways), then all those ways will maximize the probability, so the …
- 82.8k
4
votes
Accepted
Binomial GLM - non-significant difference between 100% opposite groups of observations
As for diagnosing such separation problems, there is the useful R package safeBinaryRegression. See my answer here Why does logistic regression become unstable when classes are well-separated? …
- 82.8k