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On Jan 21, 2013, at 4:36 PM, hu duan wrote:
Hi Evan,
Thanks for your quick response. I may list some interesting result.
1. The density plot on the left bottom in previous email shown red
line had a sharp peak while black not. Can you inform me what does
that difference mean?
Black = density estimate of the batch effects (used directly by non-
parametric adjustments)
Red= Normal/invgamma distributions used for the parametric adjustments
Ultimately, if the black curve in the first plot is roughly bell
shaped, you won't see much difference in the batch effect adjustments.
1. I just finished analysis of the nonparametric and parametric for
a same data. The following two plots shown here, which the Y axis is
the parametric and X axis is the nonparametric. It seems nonparametric
approach will tend to increase signal. The mean for CV for that is
1.7% while median is 0.37%. The data looks pretty close.
Yes, they are usually very similar unless the black and red lines are
very different from each other.
1.
2. For the run time, I did a PCA analysis by using all features.
The left pic shown different run times in different color, which
clearly shown run time difference. Right one is after adjust by
parametric approach. Would you consider batch effects have been
removed?
Yes, looks like the batch effects are gone.
1.
2. If I run Combat analysis in same data and use the adjust data to
run Combat again, do you think the result will be better or it will
overfitting your model? Does the model converge?
Yes, you might be overfitting a little, but the EB helps reduce the
amount of over-fitting. Also, due to you experimental design, over-
fitting shouldn't be a huge issue.
1.
Best
Tiger
<image.png>
<image.png>
2013/1/21 Johnson, William Evan <wej@bu.edu<mailto:wej@bu.edu>>
Tiger,
For question #1: The parametric plots look fine. What you are really
looking for here are major distributional deviations from these plots.
They actually look pretty good. You'll find only very small
differences between the parametric and non-parametric results. Also,
no there should not have been a plot for the non-parametric
adjustment, as it uses the empirical prior directly, so there are no
distributional assumptions to check.
Question #2: Check to see if there is a clear "run time" batch effect.
If so, compare the two step with the single step. If you have only a
few nest run times in each experiment, then the two approaches will be
very similar. I would trust the two step approach more than the one-
step method.
Hope this helps.
Evan
P.S. I hope you don't mind, I cc'd the bioconductor mailing list where
we are now using to answer questions on ComBat.
Begin forwarded message:
From: hu duan <hu.duan@asu.edu<mailto:hu.duan@asu.edu>>
Subject: about ComBat plot for non parametric
Date: January 21, 2013 3:52:46 PM EST
To: wejlab@gmail.com<mailto:wejlab@gmail.com>
Reply-To: hu.duan@asu.edu<mailto:hu.duan@asu.edu>
Hi Dr. Johnson
I am performing a microarray experiment on cancer research with
multiple run times in the two batch of arrays.
1. I have tried your Combat analysis with par.prior=T.
The attachment is the plot. There is a difference between red and
black line, I am not sure whether it can be called a major violation.
I have also tried the nonparametric one. The output was finished but
without any plot. Is that normal without a plot?. How should I judge
the nonparametric work?
2. Should I first do a Combat analysis in the same batch of slides
with multiple run time and then use the adjusted data to do with
another batch OR I could do them together?
Best
Tiger
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--
Hu Duan (Tiger)
Biological Design PhD student
Graduate Research Associate
Center for Innovation in Medicine
The Biodesign Institute, Arizona State University
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"MY MIND REBELS AT STAGNATION." -- Sherlock Holmes
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--
Hu Duan (Tiger)
Biological Design PhD student
Graduate Research Associate
Center for Innovation in Medicine
The Biodesign Institute, Arizona State University
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"MY MIND REBELS AT STAGNATION." -- Sherlock Holmes
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