[R] log transformation and mean question

From: 1Rnwb <sbpurohit_at_gmail.com>
Date: Thu, 12 May 2011 08:15:00 -0700 (PDT)


I have question about log2 transformation and performing mean on log2 data. I am doing analysis for ELISA data. the OD values and the concentration values for the standards were log2 transformed before performing the lm. the OD values for samples were log2 transformed and coefficients of lm were applied to get the log2 concentration values. I then backtransformed these log2 concentrations and the trouble started. when i take the mean of log2 concentrations the value is different than the backtransformed concentrations.

> 100+1000/2

[1] 600

> 2^((log2(100)+log2(1000))/2)

[1] 316.2278

What I am doing wrong to get the different values

--
View this message in context: http://r.789695.n4.nabble.com/log-transformation-and-mean-question-tp3517825p3517825.html
Sent from the R help mailing list archive at Nabble.com.

______________________________________________
R-help_at_r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Received on Thu 12 May 2011 - 16:18:31 GMT

This quarter's messages: by month, or sorted: [ by date ] [ by thread ] [ by subject ] [ by author ]

All messages

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Thu 12 May 2011 - 17:00:06 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.

list of date sections of archive