posted and e-mailed. On 19 Nov 2003 13:56:23 -0800, [EMAIL PROTECTED] (Dennis Roberts) wrote:
[ snip, the original Q] > > some on various lists have claimed that the coefficient of variation ... > which is usually expressed as a % of the following ratio: SD / mean ... is > a useful tool > > i have NEVER been convinced that this is so [ snip, rest] I was surprised when I first met the CoV as a measure of reliability. I thought the folks must be kidding or mistaken. If I remember right, I said something embarrassingly ignorant. Then they pointed out that it was the very efficient and effective descriptor of measurement accuracy for, say, chemical assays and bioassays: Trace amounts are measured with 10% accuracy, or 2% accuracy, or whatever. That is *the* conventional usage. So, the CoV is a very popular measure for a lot of people -- even though it was hardly mentioned in the biostatistical training that I received, and I wouldn't be surprised if it is missing entirely from books on psych-statistics. As I implied in my post of yesterday, it is especially relevant when taking the logarithm is relevant -- perhaps I should have stated it that way. I said something about "log-normal" but that is not the important facet. -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html "Taxes are the price we pay for civilization." . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
