using fitdist from fitdistplus with binomial distr

Question

I just discovered the fitdistrplus package, and I have it up and running with a Poisson distribution, etc.. but I get stuck when trying to use a binomial:

set.seed(20)
#Binomial distributed, mean score of 2
scorebinom <- rbinom(n=40,size=8,prob=.25)


fitBinom=fitdist(data=scorebinom, dist="binom", start=list(size=8, prob=mean(scorebinom)/8))

I get the error:

Error in fitdist(data = scorebinom, dist = "binom", start = list(size = 8,  : 
  the function mle failed to estimate the parameters, 
                with the error code 100
In addition: There were 50 or more warnings (use warnings() to see the first 50)

I see a lot of documentation from this package about the negative binomial distribution, but not much about the binomial. This function does appear to support this distribution (though fitdistr in MASS does not).

Any thoughts?

Answer 1

Won't you always know the number of trials (i.e., the size parameter)? If so, then try

fitBinom=fitdist(data=scorebinom, dist="binom", fix.arg=list(size=8), start=list(prob=0.3))

to estimate p and its error.