[EMAIL PROTECTED] writes:
>"Analyte concentration levels less than the limit of detection
>were assigned a value equal to the detection limit divided by the
>square root of 2 for calculation of geometric mean values.
>
>There must be a simple reason for the sqrt(2), but I'm not seeing it.
>Can someone help me out?
For a lognormal distribution, the left tail can often be approximated by a
triangular distribution. The median of a triangular distribution is the
upper limit divided by the square root of 2.
There are more sophisticated approaches, of course, to handle non-detects,
but this is simple. It seems to work better, at least in some cases, than
dividing the detection limit by 2.
There are some references for this approach, but I cannot tell you what they
are.
Steve Simon, [EMAIL PROTECTED], Standard Disclaimer.
STATS: STeve's Attempt to Teach Statistics. http://www.cmh.edu/stats
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