There are multiple ways for estimating variances. JMP uses at least two
of them (maybe more, I'm not sure) (1. Expected Mean Squares (EMS) and
2. Restricted Maximum Likelihood (REML). You can tell JMP shichc to use
on the Fit Model sccrenn. Using the EMS method it is possible to get a
negative variance estimate because the estimates are just functions of
the mean squares in the model. Using the REML method, it will most
likely estimate that component as zero (REML should not give you a
negative variance estimate). I always use REML over EMS. If your
dataset is balanced then the two methods will always give you the same
result.
Regards,
Terri
-----Original Message-----
From: jmp-l-owner@lists.biostat.wustl.edu
[mailto:jmp-l-owner@lists.biostat.wustl.edu] On Behalf Of Davern, Sean
Sent: Tuesday, August 30, 2005 3:13 PM
To: 'jmp-l@lists.biostat.wustl.edu'
Subject: Re: [jmp-l] Simple Variance Component Analysis
So what does it mean when the Lot&Random component of variance is -22%
of the total?
How is it possible for the Var Comp Est to be negative?
Sean
-----Original Message-----
From: jmp-l-owner@lists.biostat.wustl.edu
[mailto:jmp-l-owner@lists.biostat.wustl.edu]On Behalf Of
Martin_Kane@hgsi.com
Sent: Tuesday, August 30, 2005 12:51 PM
To: jmp-l@lists.biostat.wustl.edu
Subject: Re: [jmp-l] Simple Variance Component Analysis
The correct way to do this analysis is to use the "Fit Model" analysis.
Put "Response" in the Y role and put "Lot" in the Effects role. Now,
highlight "Lot" in the effects box and select the red "Attributes"
arrow. With this "Attributes" menu, select "Random Effect". This will
change the effect from "Lot" to "Lot& Random".
Doing this will allow you to get variance components out.
Unfortunately, your data set seems to have much more variability within
lot than lot-to-lot.
Sincerely,
Martin Kane
Manager, Non-Clinical Statistics
Human Genome Sciences, Inc.
240-314-4400 x3822
"Davern, Sean"
<sdavern@amgen.com> To:
"'jmp-l@lists.biostat.wustl.edu'"
Sent by:
<jmp-l@lists.biostat.wustl.edu>
jmp-l-owner@lists.biosta cc:
t.wustl.edu Subject: [jmp-l]
Simple Variance Component Analysis
08/30/2005 03:42 PM
Please respond to jmp-l
Can anyone tell me how to get JMP to give a very simply variance
component analysis?
I'm trying to quantify lot-to-lot variability of a raw material. I've
made two independent measurements of 9 lots. I'd like to segregate the
overall variance into within lot variation (coming from run-to-run
variation) and between lot (lot-to-lot) variation. I'd like the total
variance to be reported as the two components.
Attached is the example data set.
<<Example Data.JMP>>
It seems like this should be very simple but I can't seem to get the
answer without doing the calculations by hand. Thanks, Sean
Sean Davern
Engineer III
Cell Sciences Process Development
Mail Stop AW2/D2152
Ext. 57074
(See attached file: Example Data.JMP)
|