Stata The Stata listserver
[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

st: ratios first or last?


From   David Airey <david.airey@vanderbilt.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: ratios first or last?
Date   Sat, 22 Nov 2003 19:27:00 -0600

Recently I was surprised to find a difference between two methods of calculating a ratio during an experiment. Each animal has two measures taken repeatedly over time. The ratio is of the two measures. I could take the ratio at each time point, and then average the ratios to get my animal ratio. Alternatively, I could average each of the two measures and then form a ratio of the two averages, again getting my animal ratio. The second method consistently gets a higher ratio than the first method. Why would this occur? The second method is standard in my literature base.

-Dave

*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/




© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index