Propagating errors
Michael Lonetto
lonetto at cgl.ucsf.edu
Sun Jul 7 14:01:40 EST 1996
Hi,
I have a question about calculations on datasets, each with separate
errors. For example :-)
I have three data sets, each of which has a mean and a standard
deviation.
Set 1 is a control (eg, no trascription activator)
Sets 2 and 3 are results with mutant and wild type activators,
respectively.
Dividing the means of sets 2 and 3 each by set 1 provides a measure
of transcription activation.
The question is, what to do about the errors:
1) since I'm using the same set as control for both sets 2 and 3 can
I ignore the error on set 1?
2) If not, how can I combine the standard deviations? Simple combinations
(divide, multiply) do not produce reasonable numbers :-) Adding them
isn't too bad, but not of obvious validity. Should I average the
coefficients of variability and normalize them to the activation ratio?
Any way that I do this I see differences well beyond the spread of the
data, the question is what is the proper thing to do?
Sorry for posting this to bionet.software, but I remember seeing a
similar query some time back (and wondering at the time why anyone
would care :-0) I can't find any discussion of this problem in
BIOMETRY or my other statistics book. Any pointers to an appropriate
source will be appreciated.
Thanks, Mike
--
-=-=-=-=-=-=- Mike Lonetto lonetto at cgl.ucsf.edu
UCSF Dept of Stomatology, 513 Parnassus Avenue, San Francisco, CA 94143-0512
=-=-=-=-=-=-=-
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