Can anyone help me with the statistical analysis of my study on the diversity of algae and the effect of abiotic parameters? My data count has many zeros which I cannot use CCA or PCA. I researched online and mostly talked about using Extra Poisson Variation models which I have no idea as to how to do it. Need help desperately. This is my first time doing an ecological study for my project, am desperately in need of help.
The high frequency of zero means that the event is rare and this suggests a Poisson distribution. You are therefore right to use Extra Poisson Variation models. Compare the variance with the mean. If the variance is bigger than the mean it means that your data exhibit over-dispersion. In this case you should consider a negative binomial distribution.
Ette is correct. You may also want to consider a zero-inflated variant of these models (Poisson or Negative Binomial). When fitting your models, there are test statistics that you can use to determine the correct method for your data. Using these test statistics, you can justify (statistically) which model you will fit for your data.
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