Re: [R] Interpreting Q-Q Plots
On 14/05/2012 23:21, Rich Shepard wrote:
On Tue, 15 May 2012, Peter Alspach wrote:
Probably highly skewed to the right, with discrete values (perhaps
due to
the limitations in the accuracy of the assessment equipment).
Peter,
Most of these data are near zero or the lower detection limit. A few
values are very much higher. I didn't think of skewness as a reason.
But note:
library(fortunes)
fortune('chicken')
And since I don't have the experience, the only way to gain it is by
learning from those with practice reading chicken entrails.
Thanks,
Rich
I found this page helpful
http://www.cms.murdoch.edu.au/areas/maths/statsnotes/samplestats/qqplot.html
HTH
Keith J
__
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.
[R] Interpreting Q-Q Plots
My understanding of Q-Q plots is that if the tails of the plotted points fall above or below the x=y line the distribution of observed/measured values is under or over dispersed. But, how do I interpret measured values that are in horizontal lines? The attached plot illustrates this situation. TIA, Rich chromium_norm.pdf Description: Adobe PDF document __ 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.
Re: [R] Interpreting Q-Q Plots
Tena koe Rich
Probably highly skewed to the right, with discrete values (perhaps due to the
limitations in the accuracy of the assessment equipment). But note:
library(fortunes)
fortune('chicken')
HTH .
Peter Alspach
-Original Message-
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
Behalf Of Rich Shepard
Sent: Tuesday, 15 May 2012 9:53 a.m.
To: r-help@r-project.org
Subject: [R] Interpreting Q-Q Plots
My understanding of Q-Q plots is that if the tails of the plotted points
fall above or below the x=y line the distribution of observed/measured values
is under or over dispersed. But, how do I interpret measured values that are in
horizontal lines? The attached plot illustrates this situation.
TIA,
Rich
The contents of this e-mail are confidential and may be subject to legal
privilege.
If you are not the intended recipient you must not use, disseminate,
distribute or
reproduce all or any part of this e-mail or attachments. If you have received
this
e-mail in error, please notify the sender and delete all material pertaining
to this
e-mail. Any opinion or views expressed in this e-mail are those of the
individual
sender and may not represent those of The New Zealand Institute for Plant and
Food Research Limited.
__
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.
Re: [R] Interpreting Q-Q Plots
On Tue, 15 May 2012, Peter Alspach wrote:
Probably highly skewed to the right, with discrete values (perhaps due to
the limitations in the accuracy of the assessment equipment).
Peter,
Most of these data are near zero or the lower detection limit. A few
values are very much higher. I didn't think of skewness as a reason.
But note:
library(fortunes)
fortune('chicken')
And since I don't have the experience, the only way to gain it is by
learning from those with practice reading chicken entrails.
Thanks,
Rich
__
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.
Re: [R] Interpreting Q-Q Plots
And since I don't have the experience, the only way to gain it is by
learning from those with practice reading chicken entrails.
This can be hard on the chicken population.
Try comparing QQ plots for simulated random data from different distributions
with something more immediately interpretable on the measurement scale, such
as dot plots, box plots and density plots. That should add up to a fair bit of
experience quite quickly.
#Example
par(mfrow=c(1,2))
qqnorm(x-rlnorm(200, 1,0.5))
qqline(x)
plot(density(x))
qqnorm(x-rnorm(200, sample(c(0,4), 200, replace=TRUE))) #bimodal
qqline(x)
plot(density(x))
and so on.
Notice that qqnorm's vertical scale by defult corresponds to the horizontal
scale in density plots and stripcharts. I personally prefer datax=TRUE, but
really that's only a choice about whether to face north or east when reading
the entrails.
***
This email and any attachments are confidential. Any use...{{dropped:8}}
__
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.
