Hi Martin,

No, I get frequencies greather than 1.

 

See the code:

#TLC uniform

n=30

mi=1; mx=6

nrep=1000

xbar=rep(0,nrep)

for (i in 1:nrep) {xbar[i]=mean(runif(n,min=mi,max=mx))}

hist(xbar, freq=FALSE)

#hist(xbar,prob=TRUE,breaks="Sturges",xlim=c(1,6),main=paste("n =",n), xlab="Média", ylab="Probabilidade")

curve(dnorm(x,mean=mean(xbar),sd=sd(xbar)),add=TRUE,lwd=2,col="red")

 

Thanks anyway

Best

Jº

 

From: Martyn Byng [via R] [mailto:ml-node+3333757-242386738-215234@n4.nabble.com] 
Sent: quinta-feira, 3 de Março de 2011 17:12
To: jpmaroco
Subject: Re: Probabilities greather than 1 in HIST

 

Hi, 

Does 

xx = rnorm(100) 
hist(xx,freq=FALSE) 
curve(dnorm,add=TRUE) 

give you what you want? 

Martyn 
-----Original Message----- 
From: [hidden email] [mailto:[hidden email]] On Behalf Of David Winsemius 
Sent: 03 March 2011 17:00 
To: jpmaroco 
Cc: [hidden email] 
Subject: Re: [R] Probabilities greather than 1 in HIST 


On Mar 3, 2011, at 10:29 AM, jpmaroco wrote: 


> Dear David, 
> 
> Thanks for your prompt reply. 
> 
> I see your point. But how can I get a histogram with relative   
> frequencies? If I use 
> 
>> plot(xhist,yhist) 
> 
> I get absolute frequencies in the Y axis. 


In my earlier reply I meant to type yaxt="n". 

-- 
David. 


> 
> Best, 
> 
> Joao 
> 
> 
> 
> From: David Winsemius [via R] [mailto:[hidden email] 
> ] 
> Sent: quinta-feira, 3 de Março de 2011 16:01 
> To: jpmaroco 
> Subject: Re: Probabilities greather than 1 in HIST 
> 
> 
> 
> 
> On Mar 3, 2011, at 8:03 AM, jpmaroco wrote: 
> 
> 
>> Dear all, 
>> I am a newbie in R and could not find help on this problem. I am 
>> trying to 
>> plot an histogram with probabilities in the y axis. This is the code 
>> I am 
>> using: 
>> 
>> #TLC uniform 
>> n=30 
>> mi=1; mx=6 
>> nrep=1000 
>> xbar=rep(0,nrep) 
>> for (i in 1:nrep) {xbar[i]=mean(runif(n,min=mi,max=mx))} 
>> hist(xbar,prob=TRUE,breaks="Sturges",xlim=c(1,6),main=paste("n =",n), 
>> xlab="Média", ylab="Probabilidade") 
>> curve(dnorm(x,mean=mean(xbar),sd=sd(xbar)),add=TRUE,lwd=2,col="red") 
>> 
>> The problem is that I am getting greater than 1 probabilities in the 
>> Y axis? 
>> Is there a way to correct this? 
> 
> 
> Despite the argument name, which I agree suggests that probabilities 
> will be plotted, what is really described in the help page is that 
> densities will be plotted, and densities may be greater than 1. You 
> can suppress plotting of the y-axis, calculate the probabilities for 
> each of the groups returned by hist,  and then use the axes function. 
> 
>> xhist <- hist(xbar,breaks="Sturges",plot=FALSE) 
>> yhist <- xhist$counts/sum(xhist$counts) 
>> yhist 
>  [1] 0.002 0.027 0.087 0.236 0.287 0.228 0.107 0.021 0.004 0.001 
> 
> 
> 
> 
>> Many thanks in advance. 
>> Joao 
>> 
>> -- 
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> Heritage Laboratories 
> West Hartford, CT 
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David Winsemius, MD 
Heritage Laboratories 
West Hartford, CT 

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