R help - May 2011 - how to compute the inverse percentile of a given observation w.r.t. a reference distribution

Hi,

can anyone help me to figure out how to compute the percentile of an
individual observation with respect to a reference distribution.

What I mean is. Let's assume I have a vector consisting of 10 numbers
{3,5,8,1,9,5,4,3,5.5,7} and I want figure out what percentile the
number 4.9 corresponds to. I failed to find any reference to such a
function, although I would assume this must frequently be necessary.

Thanks in advance for you help.

/Rudi

On May 25, 2011, at 3:42 PM, rudi wrote:
> Hi,
>
> can anyone help me to figure out how to compute the percentile of an
> individual observation with respect to a reference distribution.
>
> What I mean is. Let's assume I have a vector consisting of 10 numbers
> {3,5,8,1,9,5,4,3,5.5,7} and I want figure out what percentile the
> number 4.9 corresponds to. I failed to find any reference to such a
> function, although I would assume this must frequently be necessary.
?quantile

Talking about percentiles when you only have 10 numbers seems rather  
misleading, don't you think?

-- 
David Winsemius, MD
West Hartford, CT

Hi Rudi,

Take a look at ?ecdf

HTH,
Jorge


On Wed, May 25, 2011 at 3:42 PM, rudi <> wrote:
> Hi,
>
> can anyone help me to figure out how to compute the percentile of an
> individual observation with respect to a reference distribution.
>
> What I mean is. Let's assume I have a vector consisting of 10 numbers
> {3,5,8,1,9,5,4,3,5.5,7} and I want figure out what percentile the
> number 4.9 corresponds to. I failed to find any reference to such a
> function, although I would assume this must frequently be necessary.
>
> Thanks in advance for you help.
>
> /Rudi
>
> ______________________________________________
> 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.
>
	[[alternative HTML version deleted]]

Hi:

On Wed, May 25, 2011 at 12:42 PM, rudi <rudi.strasser at gmail.com>
wrote:
> Hi,
>
> can anyone help me to figure out how to compute the percentile of an
> individual observation with respect to a reference distribution.
>
> What I mean is. Let's assume I have a vector consisting of 10 numbers
> {3,5,8,1,9,5,4,3,5.5,7} and I want figure out what percentile the
> number 4.9 corresponds to. I failed to find any reference to such a
> function, although I would assume this must frequently be necessary.
The simple answer is, I believe,

x <- c(3,5,8,1,9,5,4,3,5.5,7)
plot(ecdf(x))
sum(x <= 4.9)/length(x)
[1] 0.4

This would correspond to the empirical cumulative distribution
function (ecdf) to which Jorge alluded.

HTH,
Dennis
>
> Thanks in advance for you help.
>
> /Rudi
>
> ______________________________________________
> R-help at 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.
>