On 19 Nov 2003 08:53:23 -0800, [EMAIL PROTECTED] (Paul Smith) wrote: > Dear All > > Some books say that the coefficient of variation can only be used if > the random variable is positive. I would like to know why cannot one > extend the use of the same coefficient with not necessarily positive > random variables but with positive mean. Could somebody here please > help me? >
To my way of thinking, the CoV is mainly of value when the underlying data are log-normal. So, yes, the values will be positive. - I do not recall reading about it that way, but what you describe sounds like admirable advice. That is, the SD needs to *stay* proportional to the mean, or there is hardly any value in talking about its value, right? You could compute a ratio and call it a CoV. But will you have anything worthwhile, if you have values that are negative, and not natural amounts of something? So, I guess the reason that you can't, is if your journal editors and grant reviewers are apt to see it that way, too. If someone ever has a good use for a CoV on number-line data from some source, I figure they could argue for the exception for that source. This is a practical matter. -- 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/ . =================================================================
