The data looks at abundance vs rainfall. Abundance peaks at low or high rainfall. Fitting a quadratic creates a false peak at intermediate rainfall.
- What's the best type of regression to fit here?
- What type of test can I do to confirm this bimodal peak? I believe
diptestis useful for a distribution not necessarily a regression.
The first image is a fit with excluding the zeros. The second is a fit including the zeros. As you see, the second fit is zero-inflated. But that pulls down the ends of the quadratic curve and creating on what looks like a false peak.