
Dear List

I'm using Poisson GLM for the analysis of crabs data and see the correlation between BasketPortion (catch rates) and other factors such as location, sex and time. I'm new to GLM in R. I try to incorporate Date to the formula but why the coefficient for Date is NA? Another is: Does infinite AIC mean that the fitted model is inappropriate or the response and predictor need to be adjusted? Here is my code:

> crabs<-read.csv("test.csv",header=TRUE,dec=",",sep=",")
> names(crabs)
[1] "Date"                "Sex"                 "CategoryDescription" "BasketPortion"
[5] "LineOrNetNo"         "NumberOfPots"        "Longitude"           "Lat"

> Longitude<-as.numeric(levels(crabs$Longitude)[crabs$Longitude])
> Lat<-as.numeric(levels(crabs$Lat)[crabs$Lat])
> BasketPortion<-as.numeric(levels(crabs$BasketPortion)[crabs$BasketPortion])
> Date<-as.Date(levels(crabs$Date)[crabs$Date])
> glm(BasketPortion~Date+crabs$Sex+Longitude+Lat,family=poisson())

Call:  glm(formula = BasketPortion ~ Date + crabs$Sex + Longitude +
    Lat, family = poisson())

Coefficients:
(Intercept)         Date   crabs$SexM    Longitude          Lat
  -1189.749           NA        1.126       17.625       32.264

Degrees of Freedom: 18 Total (i.e. Null);  15 Residual
Null Deviance:      1.403
Residual Deviance: 0.2711       AIC: Inf
There were 19 warnings (use warnings() to see them)

Thanks in advance
Cheers
Changying


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