A very simple explanation for the observation described below would be that the cells of interest are of a different size or density than cells in the bulk population. Thus, unless one was mixing the cells periodically or continuously during the analysis, differential rates of sedimentation would affect percentages of cells acquired through a nozzle near the bottom of the sample tube. I have witnessed this effect myself and have used mixing to counteract it. Dr. Kevin G. Waddick Hughes Institute 2657 Patton Road St. Paul, MN 55113 > At 16:49 01.12.99 -0600, you wrote: > > > > > >It is really not too rare, a cell population about 0.04% to 0.15%, while the > >background is 0.01-0.05%. The problem is the variation among different > >measurements, presumably due to the systematic error. For example, I had > >10e7 total cells and ran 2*10e5 out of them for two times: one time I got > >0.04% and the other time I got 0.15%. In order to have smaller variation, > >obviously I have to increase my sample size, but the last thing I want to do > >is to run through all 10e7 cells. Can anyone give me a handy statistical > >method for estimating the sample size that makes a cost-effective > >compromise? Thank you very much. > > > >Hai Qi > >Dept. of Pathology, UTMB > > > >
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