Page 87 - Intermediate Statistics for Dummies

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Part I: Data Analysis and Model-Building Basics
Power in manufacturing
average weight shifts to, say, 2.5 ounces.
The power of a test plays a role in the manufac-
Statisticians can work backwards in calculat-
turing process. Manufacturers often have very
strict specifications regarding the size, weight,
ing the power and find the sample size they
need to know to stop the process.
and/or quality of their products. During the man-
ufacturing process, manufacturers want to be
Medical scientists also think about power when
able to detect deviations from these specifica-
they set up their studies (called clinical trials).
tions, even small ones, so they must think about
Suppose they’re checking to see whether an
how much of a difference from Ho they want
antidepressant adversely affects blood pressure
to detect, and then figure out the sample size
(as a side effect of taking the drug). Scientists
they need in order to detect that difference
need to be able to detect small differences in
when it appears. For example, if the candy bar is
blood pressure, because for some patients, any
supposed to weight 2.0 ounces, the manufac-
change in blood pressure is important to note.
turer may want to blow the whistle if the actual