[Cytometry] Proper usage of CV in data analysis

Vinko Tosevski tosevski at immunology.uzh.ch
Fri May 13 04:36:27 EDT 2011


Dear all,

The other day a colleague asked me if there's a way to assess the
clonality of her transfected cell population based on the width of the
peak she's seeing in the cytometer. While thinking about this, I came
up with some questions regarding the use of coefficient of variation
in flow cytometry for assessing the dispersion of the measured
population. I would appreciate if you could expand my perspective on
these topics...

Can I draw some conclusions about clonality of the population by just
looking at the width of the histogram peak? If yes, how and what's the
meaning of it? What do I compare it with? I assume comparing it to the
width of untransfected cells makes no sense since those ones are not
carrying the "trait" that I am looking at to begin with (not
expressing fluorochrome - tdTomato, by the way). How does one approach
this?

Looking at the peak of untransfected cells made me ask myself another
question - are CV values properly used in addressing the dispersion of
the measured fluorescent populations? I mean, those are not normally
distributed populations (they are log-normal at best) so use of CV
would be inappropriate since assumptions of normality are not met. I
guess robust CV would be the way to go, or...? But, in addition, does
any type of CV makes sense?? If I remember my textbooks correctly, CV
as a measure of dispersion only makes sense if one is dealing with
measurements of a ratio scale (in sense of statistics). Could
fluorescent measurements be actually seen as ratio scale? To me, it
sounds more like interval scale, but am I right, then, to conclude
that CV should not be used at all?!? At the moment I suggested her to
use interquartile range as a measurement, but I am really looking
forward to hearing some thoughts on this.

I appreciate your input!

Best,
Vinko


--
Vinko Tosevski
Institute of Experimental Immunology
University of Zurich, Irchel campus
Building 44, Room J42
Winterthurerstrasse 190
CH-8057 Zurich
Tel:  +41 44 6353706
Fax: +41 44 6356883
tosevski at immunology.uzh.ch


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