BD Calibur threshold behavior

Marty Bigos mbigos at
Mon Jul 23 09:35:40 EST 2001

Mario -

You got me on this one. I will look at it closer soon.

The greater effect on beads compared to cells is due to the greater
homogeneity of the bead scatter signal.


>>The "Dim cell stain" shows this artifact on dimly staining cells
>>(IF-gamma). The columns are as above. There is about a 5% decrease in
>>the percent positive - in this case not a significant change.
>>However, for other instruments, this may be greater (or less).
>Actually, there's no change.  The number of events in the first
>sample, 2902, times the percentage, 5.27, is 145.  The error in
>counting 145 events is ±12, or about 8.5 percent.  Thus, the
>precision on the 5.27% positive is ±0.44.  Simple counting statistics
>says you've done just as well.... to imply otherwise ("this may be
>greater"; "The dim cell stain shows this artifact") is misleading, if
>not outright wrong.
>Since this is a common error in many peoples' analyses, I think it
>would be great for you to "clarify" this one and explain the
>statistics.  You really should have collected a bunch more events.
>As for the rest, it is indeed interesting.  I wish you had collected
>some replicates to get some statistics on the cells.  Why is it that
>the beads show such a much greater effect than the cells?

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