This TAPPI Standard Practice provides a procedure for judging
whether suspect test determinations should be investigated further
for possible rejection. A suspect determination (apparent outlier)
is one that appears to deviate markedly from other determinations
on the same sample of material. An outlying determination (outlier)
is a suspect determination for which the deviation has, in fact,
been found to be significant using an appropriate statistical
Formal treatment of suspect test determinations, as specified in
this document, is necessary only in critical situations (e.g., very
critical research) or when required by a product specification or
an official test method.
Formal treatment of suspect test determinations and test results
is highly desirable in studies establishing the repeatability and
reproducibility of a test method (see TAPPI T 1200 "Interlaboratory
Evaluation of Test Methods to Determine TAPPI Repeatability and
Both nonstatistical and statistical rules for dealing with
suspect test determinations are given. Basically no test
determination should be accepted, no matter how correct the value
appears to be, if it is known that a faulty determination has been
made, and no test determination should be completely rejected
purely on a statistical significance test.
The statistical tests described in this practice have been
selected from a large number that are available. They apply to the
simplest kind of experimental data, that is, replicate
determinations of some property of a given sample of material.
NOTE 1: This practice applies to replicate
test determinations, usually on several specimens taken
under the same conditions and measured in a brief period of time. A
test result, obtained in accordance with a TAPPI Test Method, is
usually one or the average of two or more such test determinations
(see definitions in TAPPI T 400 "Sampling and Accepting a Single
Lot of Paper, Paperboard, Containerboard or Related Product"). This
practice allows the examination and possible elimination of suspect
test determinations (from sets of 3 to 30 determinations) before
the calculation of the final test result.
NOTE 2: This practice may also be applied to
suspect test results (by substituting the words "test
results" for "test determinations" throughout this document), when
a laboratory must evaluate a large shipment requiring the
determination and calculation of several test results.
Three categories of suspect determinations are considered:
A single suspect determination;
Two suspect determinations, one the least and the other the
greatest in the set of replicate determinations; and
Two suspect determinations, the two largest or the two smallest
in the set.
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