Solving GLM Gamma Distribution “non-positive values not allowed” Error
Problem Description
When using Generalized Linear Models (GLM) with gamma distribution, you may encounter this error:
Error: non-positive values not allowed for the 'Gamma' family
Root Cause
This error occurs due to the mathematical definition of gamma distribution:
- Gamma distribution is mathematically defined for positive values only (x > 0)
- Data containing zero or negative values makes model estimation impossible
- Predicted values that become non-positive also trigger this error
Solutions
Option 1: Data Preprocessing
If 0 or negative values are not required, remove non-positive values
Option 2: Choose Appropriate Distribution
| Data Characteristics | Recommended Model | Rationale |
|---|---|---|
| Count data | Poisson/Negative binomial | Suitable for discrete values |
| Binary outcomes | Logistic regression | For 0/1 response variables |