Bio-Tek ELx800, Operator'S Manual

Page: 106 / 214

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Chapter 3: Operation
Cutoff Formulas
A cutoff formula calculates a cutoff value that is used for classifying samples.
See Formula Type on page 70 for instructions on selecting an assay and
accessing the Cutoff formula definition screen.
During data reduction, results are evaluated against the cutoff value (with an
optional greyzone), and each well is assigned a call
POS
(positive),
NEG
(negative), or
EQUIV
(equivocal).
• One cutoff formula may be defined per assay.
•
If Transformation Formulas are defined, cutoffs are based on the
transformed results. Refer to “Defining Formula” on page 69 for the
order in which formulas are processed.
• A cutoff formula can consist of a simple numeric value (
1.500
); a well
identifier (
PC
to indicate the criterion for each of the PC replicates, or
PC;x
to indicate the average of the Positive Control replicates); or a
formula combining the two (
NC;x+0.050
).
• A “greyzone” around the cutoff value can be defined, to indicate
equivocal or indeterminate results.
• Do not use the
<
or
>
mathematical symbols in a cutoff formula.
Tip:
Choose to print a Column Report to see the greyzone and cutoff
values as well as the equations used to assign calls to samples.
Greyzone Entry
The greyzone is a definable area around the cutoff value. Samples that fall
within an area defined by the greyzone (ex. ± 5.0% of the cutoff value)
could be considered equivocal (EQUIV).
E N T E R G R E Y Z O N E : 0 5 %
Use the numeric keys to enter the greyzone percentage.
The valid entry range is from 00 to 99%. An entry of 00% indicates
no greyzone, although a sample equal to the cutoff value will still
receive the EQUIV call.
See Positive / Negative Calls on the next page for information on
how calls are assigned.
Bio-Tek Instruments, Inc.