R help - Jun 2012 - Violation of sample independence in Pearson's product-moment correlation

Hi all:

There was a concern raised by reviewers of a manuscript of mine over the
proper execution of a Pearson's correlation. In brief, this was undertaken
in order to determine the relationship between the extent of wheel running
(y axis) and ethanol intake (x axis) across three, separate 10 day periods
in 7 animals.

In the paper, the correlational plots for each 10 day-period had 70 data
points: One point for each day and each animal across 10 days of
experimentation. The reviewers, however, appropriately pointed out that
this is a violation of the assumption of sample independence for Pearson's
test, and I should have had only 7 points, which would reflect the means of
my two variables for each individual animal across 10 days. Is this
appropriate or is there a means of accounting for repeated sampling with a
correlation test?

-
Justin Montemarano
Graduate Student
Kent State University - Biological Sciences

http://www.montegraphia.com

	[[alternative HTML version deleted]]

The reviewers are right.

But this is not an R question at all. Post on a statistics list like
stats.stackexchange.com.

Much better yet, consult a local statistician, as it is abundantly
clear that you have insufficient statistical background to properly
analyze your data.

Cheers,
Bert

On Fri, Jun 1, 2012 at 10:15 AM, Justin Montemarano <jmontema at kent.edu>
wrote:
> Hi all:
>
> There was a concern raised by reviewers of a manuscript of mine over the
> proper execution of a Pearson's correlation. In brief, this was
undertaken
> in order to determine the relationship between the extent of wheel running
> (y axis) and ethanol intake (x axis) across three, separate 10 day periods
> in 7 animals.
>
> In the paper, the correlational plots for each 10 day-period had 70 data
> points: One point for each day and each animal across 10 days of
> experimentation. The reviewers, however, appropriately pointed out that
> this is a violation of the assumption of sample independence for
Pearson's
> test, and I should have had only 7 points, which would reflect the means of
> my two variables for each individual animal across 10 days. Is this
> appropriate or is there a means of accounting for repeated sampling with a
> correlation test?
>
> -
> Justin Montemarano
> Graduate Student
> Kent State University - Biological Sciences
>
> http://www.montegraphia.com
>
> ? ? ? ?[[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.


-- 

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm