# Tag Info

Accepted

### Is a "hurdle model" really one model? Or just two separate, sequential models?

Separating the log-likelihood It is correct that most hurdle models can be estimated separately (I would say, instead of sequentially). The reason is that the log-likelihood can be decomposed into ...
• 15.8k
Accepted

### Why exactly can't beta regression deal with 0s and 1s in the response variable?

Because the loglikelihood contains both $\log(x)$ and $\log(1-x)$, which are unbounded when $x=0$ or $x=1$. See equation (4) of Smithson & Verkuilen, "A Better Lemon Squeezer? Maximum-Likelihood ...
• 599

### Diagnostic plots for count regression

This is an old question, but I thought it would be useful to add that my DHARMa R package (available from CRAN, see here) now provides standardized residuals for GLMs and GLMMs, based on a simulation ...
• 8,369

### Can a model for non-negative data with clumping at zeros (Tweedie GLM, zero-inflated GLM, etc.) predict exact zeros?

Predicting the proportion of zeros I am the author of the statmod package and joint author of the tweedie package. Everything in your example is working correctly. The code is accounting correctly ...
• 13.2k

### Zero Inflated Logistic Regression - Does This Exist?

Logistic regression will not "state that all future patients do not have the disease". Logistic regression yields probabilistic predictions, i.e., probabilities that a patient has the ...
• 128k

### Zero inflated distributions, what are they really?

fit a logistic regression first calculate the probability of zeroes, and then I could remove all the zeroes, and then fit a regular regression using my choice of distribution (poisson e.g.) You're ...
• 12.7k

### Can a model for non-negative data with clumping at zeros (Tweedie GLM, zero-inflated GLM, etc.) predict exact zeros?

This answer was merged from another thread asking about predictions zero-inflated regression model, but it also applies to the Tweedie GLM model. Regression-like models predict mean of some ...
• 140k

### Zero inflated distributions, what are they really?

The basic idea you describe is a valid approach and it is often called a hurdle model (or two-part model) rather than a zero-inflated model. However, it is crucial that the model for the non-zero ...
• 15.8k

### Zero Inflated Logistic Regression - Does This Exist?

While the answer by Stephan gives a good overview of the bigger picture, I think the answer in the narrow sense is IMHO that No, zero-inflated logistic regression does not make much sense Why? Assume ...
• 2,750

### Regression predictions show far less variance than expected

Your training data - just as any other data - is a mixture of signal and noise. In modeling, we try to capture the signal, since the noise is by definition not predictable, except in a probabilistic ...
• 128k
Accepted

### R: GLMM for unbalanced zero-inflated data (glmmTMB)

A1: "All in all, I have about 33% of the dates having counts of zero, which makes me think the data is zero inflated." -> this is a common misconception - zero-inflation != lots of zeros. Zero-...
• 8,369
Accepted

### When is it appropriate to use a zero-inflated Poisson regression model?

A zero-inflated Poisson model (or any other zero-inflated model) is a special case of a mixture model, i.e., one where we model observations as coming from a mixture of two or more underlying and ...
• 128k
Accepted

### Type I and Type II negative binomial distribution in zero inflated negative binomial (ZINB) model

The difference between these two model families is the relationship between mean and variance. nbinom1 (also called quasi-poisson) variance = µ * phi where µ is the mean and phi is the over-...
• 385
Accepted

### Zero inflated beta regression using gamlss for vegetation cover data

I have added preliminary support for gamlss to the emmeans package... ...
• 20.8k
Accepted

### hurdle model with non-zero gaussian distribution in R

If you want to model data that essentially follow a normal distribution for the positive values but have a point mass at zero, you could start with a Gaussian model censored at zero. In the ...
• 15.8k

### Zero-inflated Poisson regression Vuong test: Raw, AIC- or BIC-corrected results

I am convinced that it is incorrect to use the Vuong test -- in any of its forms -- as a test for zero-inflation. I have had a paper "The misuse of the Vuong test for non-nested models to test for ...
• 166

### Zero inflated distributions, what are they really?

What ssdecontrol said is very correct. But I'd like to add a few cents to the discussion. I just watched the lecture on Zero Inflated models for count data by Richard McElreath on YouTube. It makes ...
• 1,622
Accepted

### GAMM with zero-inflated data

In addition to mgcv and its zero-inflated Poisson families (ziP() and ziplss()), you might also look at the brms package by Paul-...
• 49.2k
Accepted

### Zero-inflated Gaussian for weights below zero recorded as 0?

I think the model is more appropriately a left-censored Gaussian, since the process you describe is about discarding information below some value (in this case, the location is known to be 0, which is ...
• 92.4k

### How do I deal with many zero values in terms of correlation?

Because you are comparing simulated vs. true values, a correlation between the two is not the best way to evaluate the quality of your simulations. This is easy to illustrate: imagine your model is ...
• 18.9k

### When is it appropriate to use a zero-inflated Poisson regression model?

Poisson regression sucks, but zero-inflating your models is fine As previously discussed here, here and here the Poisson regression is almost always a bad count model and is far inferior to the ...
• 129k

### Dealing with 0,1 values in a beta regression

I think the actual "correct" answer to this question is zero-one inflated beta regression. This is designed to handle data that vary continuously on the interval [0,1], and allows many real 0's and 1'...
• 1,242
Accepted

### Use loess regression with many zero values

A Loess confidence interval doesn't mean much unless the Loess parameters have been cross-validated (which usually is not the case). When you use Loess for exploration, as it was originally intended, ...
• 329k
Accepted

### Is a distribution still considered right-skewed if the majority of responses are zero?

This is certainly possible. The most common definition for a distribution to be right skewed is that the skewness $$\gamma_1 := E\bigg(\Big(\frac{X-\mu}{\sigma}\Big)^3\bigg)$$ be positive. For ...
• 128k
Accepted

### How do I deal with many zero values in terms of correlation?

Zero is a value like any other value to each kind of correlation. Each correlation takes zeros into account in its way: as implying a deviation from the mean of either variable in the case of Pearson ...
• 58.4k

### Standard negative binomial regression when counts are mainly zeros?

I don't quite think that a distinction between "true" and "untrue" ("false"?) zeros is very helpful. Zero inflated distributions arise naturally if your data generating ...
• 128k

### How to test for Zero-Inflation in a dataset?

The score test (referenced in the comments by Ben Bolker) is performed by first calculating the rate estimate $\hat{\lambda}= \bar{x}$. Then count the number of observed 0s denoted $n_0$ and the total ...
• 4,299
Accepted

### Can you use glmmTMB to simultaneously model offsets and zero-inflation?

tl;dr as far as I can tell at this point, ...
• 44.6k
Accepted

### Small Sample Sizes and Zero Inflated Count Data in R

The problem you are observing with lack of significance of GA has nothing to do with zero inflation or with random effects. It is simply a limitation of Wald tests for count models. If you replace the ...
• 13.2k