9. Precision and Bias
9.1 Precision—In an interlaboratory test of this test method
with three different films on panels, ten laboratories and
operators, and repeated by switching leads and panels between
laboratories, the within-laboratory standard deviation was
found to be 0.52 and the between-laboratory standard deviation
was found to be 0.61. Based on these standard deviations, the
following criteria should be used for judging the acceptability
of results at a 95 % confidence level:
9.1.1 Repeatability—Two results obtained by two operators
within a laboratory using the same pencils and panels should be
considered suspect if they differ by more than one pencil unit
on the scale described in 5.1.
9.1.2 Reproducibility—Two results, each the mean of at
least two determinations, obtained by operators in different
laboratories using the same pencils and panels or different
pencils with the same panels should be considered suspect if
they differ by more than one pencil unit on the scale described
in 5.1.
9.1.3 Bias—Since there is no acceptable material suitable
for determining the bias for the procedure in this test method
for measuring pencil hardness, bias cannot be determined.