quantile question

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Read the help page for the quantile function (the whole page, there is a lot of good detail in there), the 2nd reference on the page should also be a helpful read.
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of ANJAN PURKAYASTHA
> Sent: Thursday, January 22, 2009 9:52 AM
> To: r-help at r-project.org
> Subject: [R] quantile question
> 
> Hi,
> A simple quantile question:
> I need to calculate the 95% and 5% quantiles (aka percentiles) for the
> following data:
> 67.12
> 64.51
> 62.06
> 55.45
> 51.41
> 43.78
> 10.74
> 10.14
> 
> if I use the formula: 95% quantile point= 95 (8+1)/100, I get the
> 8.55th
> point as the 95% quantile. Which does not make too much sense as I have
> only
> 8 data points.
> The other option is to use (95*8)/100 = 7.6th data point (which can be
> found
> by interpolation between the 7th and 8th data points).
> Reportedly, the second formula is not too accurate. However in my case
> the
> first formula does not make much sense.
> 
> Any advice?
> 
> TIA,
> Anjan
> 
> --
> =============================
> anjan purkayastha, phd
> bioinformatics analyst
> whitehead institute for biomedical research
> nine cambridge center
> cambridge, ma 02142
> 
> purkayas [at] wi [dot] mit [dot] edu
> 703.740.6939
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> 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.
have a look at the online help file of ?quantile(); check also:

x <- c(67.12, 64.51, 62.06, 55.45, 51.41, 43.78, 10.74, 10.14)
sapply(1:9, function (i) quantile(x, c(0.05, 0.95), type = i))

I hope it helps.

Best,
Dimitris
Hi,
A simple quantile question:
I need to calculate the 95% and 5% quantiles (aka percentiles) for the
following data:
67.12
64.51
62.06
55.45
51.41
43.78
10.74
10.14

if I use the formula: 95% quantile point= 95 (8+1)/100, I get the 8.55th
point as the 95% quantile. Which does not make too much sense as I have only
8 data points.
The other option is to use (95*8)/100 = 7.6th data point (which can be found
by interpolation between the 7th and 8th data points).
Reportedly, the second formula is not too accurate. However in my case the
first formula does not make much sense.

Any advice?

TIA,
Anjan

Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
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