Hi!
With the following script, I'm trying to make a demonstration of a
Confidence Interval, but I'm observing some differences on tails.
# Teste de média entre uma amostra e uma população normal
# Autor: Raphael de Freitas Saldanha
# Agosto de 2008
n <- 200 # Sample size
xbar <- 100 # Sample mean
s <- 2 # Sample SD
nc <- 0.95 # Confidence level (95% -> 0.95)
rep <- 1000 # Loops
#######################################################################
y <- NULL # Vetor com as médias da amostra
for (i in 1:rep){ # Loop
x <- rnorm(n,xbar,s) # Gere uma amostra normal n elementos, xbar média e
s desvio-padrão
x <- mean(x) # Calcule a média (exata) dessa amostra
y <- c(y,x) # Coloque essa média em um registro em y
}
y <- sort(y) # Ordene todas as médias geradas
LI <- y[((1-nc)/2)*rep] # Limite inferior,
LS <- y[rep-(((1-nc)/2)*rep)] # Limite superior
### PARTE GRÁFICA ###
x <- mean(y)
xvals <- seq(-LI, LI, length.out=5000)
dvals <- dnorm(xvals,mean(y), sd(y))[1:5000]
xbvals <- seq(LS, LS*2, length.out=5000)
dbvals <- dnorm(xbvals,mean(y), sd(y))[1:5000]
ahist <- hist(y, freq=FALSE, col="lightblue", main="Intervalo de confiança")
polygon(c(xvals,LI,LI), c(dvals,dnorm(LI,mean(y), sd(y)),min(dvals)),
col="orange", lty=0)
polygon(c(LS,LS,xbvals), c(min(dbvals),dnorm(LS,mean(y), sd(y)),dbvals),
col="orange", lty=0)
curve(dnorm(x,mean(y), sd(y)),add=TRUE, lty=1, col="red",lwd=2)
### Intervalo de Confiança ###
LI # Limite inferior
LS # Limite superior
--
Atenciosamente,
Raphael Saldanha
[EMAIL PROTECTED]
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
