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- Original Message
From: Michele Scardi <[EMAIL PROTECTED]>
To: ECOLOG-L@LISTSERV.UMD.EDU
Sent: Monday, January 14, 2008 4:58:18 AM
Subject: Re: [ECOLOG-L] Data set with many many zeros. Help?
Monday, January 14, 2008, 4:11:24 AM, Warren Aney wrote:
WWA> Bill, are we the Ludd
Jim R and Michele hit on very important and related points.
I almost wrote in my original reply that:
"If the critters being sampled in the quadrats are mobile, you'll need to
verify that your ability to detect (and count) them is 100% and does not
vary by quadrat (perhaps as a function of the
- Original Message ----
Subject: Re: Data set with many many zeros. Help?
Date: Sun, 13 Jan 2008 18:38:41 +0200
From: Anon. <[EMAIL PROTECTED]>
To: Highland Statistics Ltd. <[EMAIL PROTECTED]>
References: <[EMAIL PROTECTED]>
Highland Statistics Ltd. wrote:
> On Sat, 12
Monday, January 14, 2008, 4:11:24 AM, Warren Aney wrote:
WWA> Bill, are we the Luddites in this arena? I agree with you, and my
WWA> statistics professor would have taken it one important step further:
Choose
WWA> your statistical analysis methods before you start collecting your data --
WWA> ..
y
> Senior Wildlife Ecologist
> Tigard, Oregon
>
> -Original Message-
> From: Ecological Society of America: grants, jobs, news
> [mailto:[EMAIL PROTECTED] Behalf Of William Silvert
> Sent: Sunday, January 13, 2008 1:57 PM
> To: ECOLOG-L@LISTSERV.UMD.EDU
> Subject: Re: D
While you are right that the technique should be what is emphasized,
many people are not familiar with generalized linear models (as
opposed to general linear models), and even less are familiar with
how to use them with their stats software of choice. Many pieces of
software that are more
igard, Oregon
-Original Message-
From: Ecological Society of America: grants, jobs, news
[mailto:[EMAIL PROTECTED] Behalf Of William Silvert
Sent: Sunday, January 13, 2008 1:57 PM
To: ECOLOG-L@LISTSERV.UMD.EDU
Subject: Re: Data set with many many zeros. Help?
One point about the va
Bill,
As far as I could tell all of the responses were directed at
techniques/models (zero-inflated models, generalized linear models, etc.).
Some folks offered ways to use those techniques in various common software
packages, but I don't see how that's a bad thing or that it shows any
relianc
One point about the various replies to this and other posts that disturbs me
is the focus of the responses. It used to be that statistical questions were
answered in terms of statistical techniques, such as regression or ANOVA or
t-tests. Now the answers are phrased in terms of software - SAS, R
Stephen,
You'd be one of the lucky ones if your data actually fit a Poisson. You'll
probably find some level of overdispersion and need to handle that with,
e.g., a negative binomial or gamma distribution. Either way, for some
methods to handle those zeros in a flexible way, check out the excel
If you have access to SAS, Proc GLIMMIX generalizes Procs Genmod and
Mixed, allowing hierarchical random effects and various link
functions and error distributions. Like Proc Genmod, it is
well-suited for binomial (logistic) or count data and allows a
poisson (overdispersed or not) distribution
On Sat, 12 Jan 2008 15:38:33 -0400, Stephen Cole <[EMAIL PROTECTED]> wrote:
>Hello Ecolog - I was wondering if anyone had any advice on the following
>problem.
>
>I have a data set that is infested by a plague of zeros that is causing me
>to violate all assumptions of classic parametric testing.
Jonathan Coop's advice -- linear model with Poisson data-- is good. I would add
that I think you are
approaching your data the wrong way -- you admit that your zeros are good data,
and so they are
neither a 'plague,' nor something that can, or should, be 'cleaned up.' Find
the statistical mode
sampling design. =20
=20
hope this helps
=20
Jonathan> Date: Sat, 12 Jan 2008 15:38:33 -0400> From: [EMAIL PROTECTED]> S=
ubject: [ECOLOG-L] Data set with many many zeros. Help?> To: [EMAIL
PROTECTED]
ISTSERV.UMD.EDU> > Hello Ecolog - I was wondering if anyone had any advice
Saturday, January 12, 2008, 8:38:33 PM, Stephen Cole wrote:
SC> I have a data set that is infested by a plague of zeros that is causing me
SC> to violate all assumptions of classic parametric testing. ...
Stephen,
if you're measuring density, abundance or such and you end up with
many zeros and s
Hello Ecolog - I was wondering if anyone had any advice on the following
problem.
I have a data set that is infested by a plague of zeros that is causing me
to violate all assumptions of classic parametric testing. These are true
zeros in that the organisms in question did not occur in my randoml
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