R help - Jul 2013 - How to determine the pdf of a gamma distribution using the estimated parameters?

Hello everyone,

With th bar histogram (number of occurrences) hist<-c(24,7,4,1,2,1,1) of
seven equally spaces classes ]1-4], ]5-8], ]9-12], ]13-16], ]17-20], ]21-24],
]25-28], I obtained shape=0.8276 and rate=0.1448.

I would like to know how to build the continuous pdf of a this gamma
distribution knowing these two estimated parameters such that I will be able to
predict the pdf of any positive value.

Thanks
Armel

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Kaptue Tchuente, Armel <armel.kaptue <at> sdstate.edu> writes:
> 
[snip]
> With th bar histogram (number of occurrences)
>  hist<-c(24,7,4,1,2,1,1) of seven equally spaces classes
> ]1-4], ]5-8], ]9-12], ]13-16], ]17-20], ]21-24], ]25-28], 
> I obtained shape=0.8276 and rate=0.1448.
> 
> I would like to know how to build the continuous pdf of a this
> gamma distribution knowing these two estimated
> parameters such that I will be able to predict the pdf of any
> positive value.
  Are you talking about dgamma(x,shape=0.8276,rate=0.1448),
where x is the value you are trying to predict for?  dgamma gives
probability density, pgamma gives cumulative density/distribution
function.

Sorry not to be more precise in my previous message.
My question is how to use dgamma with the obtained shape and scale parameters in
order to approximate the observed pdf since the results of dgamma (seq(4,28,4),
shape,rate) are very different from the observed pdf [pdf obs_pdf<-c(0.600,
0.175, 0.100, 0.025, 0.050, 0.025, 0.025)]?
Armel

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Ben Bolker
Sent: Friday, July 12, 2013 11:58 AM
To: r-help at stat.math.ethz.ch
Subject: Re: [R] How to determine the pdf of a gamma distribution using the
estimated parameters?

Kaptue Tchuente, Armel <armel.kaptue <at> sdstate.edu> writes:
> 
[snip]
> With th bar histogram (number of occurrences)
>  hist<-c(24,7,4,1,2,1,1) of seven equally spaces classes ]1-4], ]5-8], 
> ]9-12], ]13-16], ]17-20], ]21-24], ]25-28], I obtained shape=0.8276 
> and rate=0.1448.
> 
> I would like to know how to build the continuous pdf of a this gamma 
> distribution knowing these two estimated parameters such that I will 
> be able to predict the pdf of any positive value.
  Are you talking about dgamma(x,shape=0.8276,rate=0.1448),
where x is the value you are trying to predict for?  dgamma gives probability
density, pgamma gives cumulative density/distribution function.

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