Regarding the use of mean channel values on log data: When data is collected using log amplifiers and displayed on a log scale it makes sense to use the median rather than the mean channel values as a method of measuring changes in fluorescence intensity. When data displayed on a log scale looks like a normal distribution it means that the underlying linear data is actually skewed toward lower intensity values. The problem with calculating the mean using log channel values is that it the mean log channel value is not the same as taking the log of the mean channel values. The median is a more robust measurement particularly when working with log channel values. For a much more complete explaination of the use of mean, CV, median, and robust CV see pages 194-195 of the 3rd edition of Practical Flow Cytometry by Howard Shapiro. If we are lucky when Howard returns from his current meeting he will post a much more complete answer. Nancy Perlmutter At 03:47 PM 3/19/01 -0500, Falco, Vincent wrote: >Group > >I have an investigator that wants to use mean channel value on a log scale >as a measure of changes in fluorescent intensity and thereby a surrogate >measure for changes in the surface marker antigen. Can I solicit any and all >thoughts and criticism. >Thanks in advance. >Vin Falco ************************************************** Nancy Perlmutter ngp@shapirolab.com Laboratory Manager Howard M. Shapiro, MD, PC 119 Braintree Street, Suite 102 Allston, MA 02134 phone 617-783-8392 fax 617-783-4750 **************************************************
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