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I am dealing with a very hard-to-work data set: fish larval density. It is a semicontinuous data, with 90% of zeros and a right-skewed distribution, with very very large values.

One problem is that my zeros have two sources: true and false, or structural and sampling.

I saw models that can deal with these two types of zeros, called Zero inflated models, but only for count data. I didn't see model for semicontinuous data that can deal with false zeros. These models are two-part models with log-normal or gamma distribution, and all of them assume true zeros.

Any help, please?

Here is a part of my data set: My response is fish larval density (Dprochilodus). And I have a lot of zeros, but I can't assume that all of them are trully zeros. What I want to tell is: when I have zero, it doesn't mean there were no larvae. Can be because I could't sample/detect them. Here there are some explanations about the different models for true and false zeros

ponto            Dprochilodus      periodo    Dif_his.y            temp      
 Length:574         Min.   :  0.0000   I :278   Min.   :0.01571   Min.   :21.00  
 Class :character   1st Qu.:  0.0000   II:296   1st Qu.:0.09738   1st Qu.:24.00  
 Mode  :character   Median :  0.0000            Median :0.22505   Median :27.00  
                    Mean   :  0.5949            Mean   :0.25405   Mean   :26.87  
                    3rd Qu.:  0.0000            3rd Qu.:0.40296   3rd Qu.:29.01  
                    Max.   :134.7469            Max.   :0.89746   Max.   :33.00
Fernanda Silva
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  • Hello and welcome to stack overflow. Please provide minimally reproducible example of your issue https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example – boski Feb 26 '19 at 12:44
  • You might want to ask the same question on the sister site cross validated. I've used Tobit models for continuous zero inflated data, but I did not run across your false zeroes problem. Good luck! – Nova Feb 26 '19 at 13:26
  • Thank you @Nova. I seems that Tobit is not the best model for me. Cross validated uses to hold my questions because that there are out of topic. But I will try again. – Fernanda Silva Feb 26 '19 at 14:46
  • @boski,I added more details – Fernanda Silva Feb 26 '19 at 15:30

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