# Tagged Questions

Refers generally to statistical procedures that utilize the logistic function, most commonly various forms of logistic regression

27k views

### Difference between logit and probit models

What is the difference between the logit and the probit model? I'm more interested here in knowing when to use logistic regression, and when to use probit. If there's any literature which define it ...
21k views

### Which pseudo-$R^2$ measure is the one to report for logistic regression (Cox & Snell or Nagelkerke)?

I have a SPSS Output for a logistic regression. This output reports two measure for the model fit, Cox & Snell and ...
3k views

### How to deal with perfect separation in logistic regression?

If you have a variable which perfectly separates zeroes and ones in target variable, R will yield the following "perfect or quasi perfect separation" warning message: ...
2k views

### Simulation of Logistic Regression Power Analysis - Designed Experiments

This question is in response to an answer given by @Greg Snow in regards to a question I asked concerning power analysis with logistic regression and SAS Proc GLMPOWER. If I am designing an ...
1k views

### Interpretation of simple predictions to odds ratios in logistic regression

I'm somewhat new to using logistic regression, and a bit confused by a discrepancy between my interpretations of the following values which I thought would be the same: exponentiated beta values ...
5k views

### Does an unbalanced sample matter when doing logistic regression?

Okay, so I think I have a decent enough sample, taking into account the 20:1 rule of thumb: a fairly large sample (N=374) for a total of 7 candidate predictor variables. My problem is the following: ...
675 views

### Logistic regression in R resulted in Hauck Donner phenomenon. Now what?

I'm trying to predict a binary outcome using 50 continuous explanatory variables (the range of most of the variables is -∞ to ∞). My data set has almost 24,000 rows. When I run glm in R, I get: ...
3k views

### What is the difference between generalized estimating equations and GLMM?

I'm running a GEE on 3-level unbalanced data, using a logit link. How does this differ (in terms of the conclusions I can draw and the meaning of the coefficients) from a GLM with mixed effects ...
1k views

### Model Selection: Logistic Regression

Suppose we have $n$ covariates $x_1, \dots, x_n$ and a binary outcome variable $y$. Some of these covariates are categorical with multiple levels. Others are continuous. How would you choose the ...
164 views

### Does down-sampling change logistic regression coefficients?

If I have a dataset with a very rare positive class, and I down-sample the negative class, then perform a logistic regression, do I need to adjust the regression coefficients to reflect the fact that ...
984 views

### Graphing a Probability Curve for a Logit Model With Multiple Predictors

I have the following probability function: $$\text{Prob} = \frac{1}{1 + e^{-z}}$$ where $$z = B_0 + B_1X_1 + \dots + B_nX_n.$$ My model looks like \Pr(Y=1) = \frac{1}{1 + \exp\left(-[-3.92 + ...
9k views

### Logistic Regression in R (Odds Ratio)

I'm trying to undertake a logistic regression analysis in R. I have attended courses covering this material using STATA. I am finding it very difficult to replicate ...
5k views

### How to carry out multiple post-hoc chi-square tests on a 2 X 3 table?

My data set is comprised of either total mortality or survival of an organism at three site types, inshore, midchannel and offshore. The numbers in the table below represent the number of sites. ...
1k views

### Power analysis for ordinal logistic regression

I am looking for a program (in R or SAS or standalone, if free or low cost) that will do power analysis for ordinal logistic regression.
8k views

### How to interpret main effects when the interaction effect is not significant?

I ran a Generalized Linear Mixed Model in R and included an interaction effect between two predictors. The interaction was not significant, but the main effects (the two predictors) both were. Now ...
3k views

### R package for fixed-effect logistic regression

I'm looking for an R package for estimating the coefficients of logit models with individual fixed-effect (individual intercept) using Chamberlain's 1980 estimator. ...
1k views

### When is logistic regression solved in closed form?

Take $x \in \{0,1\}^d$ and $y \in \{0,1\}$ and suppose we model the task of predicting y given x using logistic regression. When can logistic regression coefficients be written in closed form? One ...
1k views

### Assessing logistic regression models

This question arises from my actual confusion about how to decide if a logistic model is good enough. I have models that use the state of pairs individual-project two years after they are formed as a ...
4k views

### Multiple Chi-Squared Tests

I have cross classified data in a 2 x 2 x 6 table. Let's call the dimensions response, A and ...
6k views

### Reporting results of a logistic regression

I have the following logistic regression output: ...
2k views

### Case weighted logistic regression

I'm looking at a few logistic regression issues. ("regular" and "conditional"). Ideally, I'd like to weight each of the input cases so that the glm will focus more on predicting the higher weighted ...
221 views

### Enormous coefficients in logistic regression - what does it mean and what to do?

I get enormous coefficients during logistic regression, see coefficients with krajULKV: ...
2k views

### Interpretation of log transformed predictors in logistic regression

One of the predictors in my logistic model has been log transformed. How do you interpret the estimated coefficient of the log transformed predictor and how do you calculate the impact of that ...
270 views

### Significance of categorical predictor in logistic regression

I am having trouble interpreting the z values for categorical variables in logistic regression. In the example below I have a categorical variable with 3 classes and according to the z value, CLASS2 ...
1k views

### Diagnostics for logistic regression?

For linear regression, we can check the diagnostic plots (residuals plots, Normal QQ plots, etc) to check if the assumptions of linear regression are violated. For logistic regression, I am having ...
3k views

### Poisson regression to estimate relative risk for binary outcomes

Brief Summary Why is it more common for logistic regression (with odds ratios) to be used in cohort studies with binary outcomes, as opposed to poisson regression (with relative risks)? Background ...
2k views

### Why use Platt's scaling?

In order to calibrate a confidence level to a probability in supervised learning (say to map the confidence from an SVM or a decision tree using oversampled data) one method is to use Platt's Scaling ...
2k views

### Stepwise logistic regression and sampling

I am fitting a stepwise logistic regression on a set of data in SPSS. In the procedure, I am fitting my model to a random subset that is approx. 60% of the total sample, which is about 330 cases. ...
5k views

### How to do logistic regression subset selection?

I am fitting a binomial family glm in R, and I have a whole troupe of explanatory variables, and I need to find the best (R-squared as a measure is fine). Short of writing a script to loop through ...
512 views

### Are robust methods really any better?

I have two groups of subjects, A, and B, each with a size of approximately 400, and about 300 predictors. My goal is to build a prediction model for a binary response variable. My customer wants to ...
2k views

What's the difference between terms 'link function' and 'canonical link function'? Also, are there any (theoretical) advantages of using one over the other? e.g. A binary response variable can be ...
442 views

### Properties of logistic regressions

We're working with some logistic regressions and we have realized that the average estimated probability always equals the proportion of ones in the sample; that is, the average of fitted values ...
2k views

### Hosmer-Lemeshow vs AIC for logistic regression

If the Hosmer-Lemeshow indicates a lack of fit but the AIC is the lowest among all the models....should you still use the model? If I delete a variable, the Hosmer-Lemeshow statistic is not ...
6k views

### Logistic regression model does not converge

I've got some data about airline flights (in a data frame called flights) and I would like to see if the flight time has any effect on the probability of a ...
4k views

### Logistic Regression - Multicollinearity Concerns/Pitfalls

In Logistic Regression, is there a need to be as concerned about multicollinearity as you would be in straight up OLS regression? For example, with a logistic regression, where multicollinearity ...
199 views

### Updating classification probability in logistic regression through time

I am building a predictive model that forecasts a student's probability of success at the end of a term. I’m specifically interested in whether the student succeeds or fails, where success is usually ...
2k views

### How to simulate artificial data for logistic regression?

I know I'm missing something in my understanding of logistic regression, and would really appreciate any help. As far as I understand it, the logistic regression assumes that the probability of a '1' ...
343 views

### Interpreting a logistic regression model with multiple predictors

I performed multivariate logistic regression with the dependent variable Y being death at a nursing home within a certain period of entry and got the following ...
304 views

### Is the Mundlak fixed effects procedure applicable for logistic regression with dummies?

I have a dataset with 8000 clusters and 4 million observations. Unfortunately my statistical software, Stata, runs rather slowly when using its panel data function for logistic regression: ...
1k views

### How to do logistic regression in R when outcome is fractional?

I'm reviewing a paper which has the following biological experiment. A device is used to expose cells to varying amounts of fluid shear stress. As greater shear stress is applied to the cells, more of ...
2k views

### Better Classification of default in logistic regression

Full Disclosure: This is homework. I've included a link to the dataset ( http://www.bertelsen.ca/R/logistic-regression.sav ) My goal is to maximize the prediction of loan defaulters in this data set. ...
774 views

### How to fit Bradley–Terry–Luce model in R, without complicated formula?

The Bradley–Terry–Luce(BTL) model states that $p_{ji} = logit^{-1}(\delta_j - \delta_i)$, where $p_{ij}$ is the probability that object $j$ is judged to be "better", heavier, etc, than object $i$, ...
745 views

### How do you predict a response category given an ordinal logistic regression model?

I want to predict a health problem. I have 3 outcome categories that are ordered: 'normal', 'mild', and 'severe'. I wish to predict this from two predictor variables, a test result (a continuous, ...
2k views

### Logistic Regression: Classification Tables a la SPSS in R

In SPSS output there is a pretty little classification table available when you perform a logistic regression, is the same possible with R? If so, how?
1k views

### Multinomial logistic regression vs binary logistic regression

Lets say we have a dependent variable $Y$ with few categories and set of independent variables. What are the advantages of Multinomial logistic regression over set of binary logistic Regressions? ...
2k views

### Stepwise model selection, Hosmer-Lemeshow statistics and prediction success of model in nested logistic regression in R

is it possible to do stepwise (direction = both) model selection in nested binary logistic regression in R? I would also appreciate if you can teach me how to get: Hosmer-Lemeshow statitistic, Odds ...
500 views

### Consequences of an improper link function in N alternative forced choice procedures (e.g. 2AFC)?

Background: In some cognitive psychology research areas N-alternative forced choice tasks are common. The most common of these is a two alternative forced choice (2AFC). This usually takes the form ...
815 views

### Logistic vs linear regression

Let's say I run a linear regression model with a binary dependent variable. If I ran logistic regression on the same data would the results be comparable or exactly similar? By results I mean both the ...