398 CHAPTER 6 Inferential Statistics
(E)
Type I error: get drenched
Type II error: carry an umbrella, and it rains- Mr. Surowski’s grading policies have come under attack by the
Central Administration as well as by the Board of Directors of
SAS. To analyze the situation, a null hypothesis together with an
alternative hypothesis have been formulated:
H 0 : Mr. Surowski’s grading policies are fair
Ha: Mr. Surowski plays favorites in awarding grades.
The Board of Directors finds no irregularities, and therefore takes
no actions against him, but the rumors among the students is that
it is advantageous for Mr. Surowski’s students to regularly give
him chocolate-covered expresso coffee beans. If the rumors are
true, has an error been made? If so, which type of error? - An assembly-line machine produces precision bolts designed to
have a mean diameter of 8.1 mm. Each morning the first 50 bear-
ings produced are pulled and measured. If their mean diameter
is under 7.8 mm or over 8.4 mm, the machinery is stopped and
the foreman is called on to make adjustments before production is
resumed. The quality control procedure may be viewed as a hy-
pothesis test with the null hypothesisH 0 : μ= 8.1. The engineer
is asked to make adjustments when the null hypothesis is rejected.
In test terminology, what would be the result of a Type II error
(choose one)?
(A) A warranted halt in production to adjust the machinery
(B) An unnecessary stoppage of the production process
(C) Continued production of wrong size bolts
(D) Continued production of proper size bolts
(E) Continued production of bolts that randomly are the right or
wrong size