[R] Temporal Analysis of variable x; How to select the outlier threshold in R?

[Melanie Vida]

--- bogdan romocea <br44114 at yahoo.com> wrote:

 > I'm not sure I understand.
 > You have financial data and want to throw away some
 > outliers??
 > Why would you ever do this?

I would select an outlier threshold, to extract a subset of the data "x" 
that had significant difference in financial contributions in a range of 
two years. "x" represents a variable for the amount of dollar value 
change in allocations to an account over a 2 year period.

 >
 > First of all, I'd suggest you pay close attention to
 > what the data is
 > trying to say. Maybe your distribution is not normal
 > after all (see
 > tests for normality etc). Maybe you shouldn't force
 > your normality
 > assumption upon the data.
 >

A plot off qq.plot(x) or qqnorm(x) indicated that the data was not 
normally distributed. I also used shapiro.test() which gave a p-value << 
0.05.

In order to select the outlier threshold, I ended up using the following :
outlier_threshold <- qauntile(x, 3/4) + 1.5* IQR(x)


-Melanie

 >
 >
 > -----Original Message-----
 > From: Melanie Vida [mailto:mvida at mitre.org]
 > Sent: Friday, February 25, 2005 1:30 PM
 > To: r-help
 > Subject: [R] Temporal Analysis of variable x; How to
 > select the outlier
 > threshold in R?
 >
 >
 > For a financial data set with large variance, I'm
 > trying to find the
 > outlier threshold of one variable "x" over a two
 > year period. I
 > qqplot(x2001, x2002) and found a normal
 > distribution. The latter part
 > of
 > the normal distribution did not look linear though.
 > Is there a suitable
 >
 > method in R to find the outlier threshold of this
 > variable from 2001
 > and
 > 2002  in R?
 >
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