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Re: st: RE: AW: ratio function


From   Steve Samuels <sjsamuels@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: AW: ratio function
Date   Thu, 1 Apr 2010 09:30:10 -0400

2010/4/1 Roman Kasal <kasal@trexima.cz>:
>
> but it ignores unpaired data :(

And it should.   Data (x,y) (1,2) (2,4) (3,6) (100,.)    will give an
entirely different view of the data if the unpaired observation is
included in a mean or ratio calculation.  Or consider data with x
missing in half the pairs and y missing in the other half; the ratio
of means would be meaningless.

The formulas for standard errors for ratios  assume that the data are
paired. Formally, they are based on the residual MSE of a regression
of y on x through the origin. You cannot do that regression with
unpaired data.

If your concern is missing data, the solution is to impute the missing
values before analysis.

Steve
>
>
Steven Samuels
sjsamuels@gmail.com
18 Cantine's Island
Saugerties NY 12477
USA
Voice: 845-246-0774
Fax:    206-202-4783
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