AP® Statistics 2021 Scoring Guidelines
© 2021 College Board
Model Solution Scoring
(a)
Section
3
Because the p-value is greater than
the null hypothesis should not be rejected. The
results from this study do not provide
convincing statistical evidence that the
manager’s belief is correct. That is, there is not
convincing statistical evidence that more than
40 percent of all customers of the pet supply
company would place an order within 30 days
after receiving an e-mail with a coupon for $10
off the next purchase.
Essentially correct (E) if the response satisfies
the following two components:
1. Provides a correct justification of the
conclusion based on whether the p-value is
less than
(or a comparison of the
value of the test statistic to an appropriate
critical value, e.g.,
)
2. States a correct conclusion consistent with
the stated alternative hypothesis OR states a
conclusion that answers the inference
question (e.g., states the conclusion in terms
of the manager’s belief)
Partially correct (P) if the response satisfies
only one of the two components.
Incorrect (I) if the response does not meet the
criteria for E or P.
Additional Notes:
• Although including proper context (the concept of population proportion and referencing the response
variable) is important in stating the conclusion, context displayed in stating the conclusion is considered
in scoring component 2 of Section 1.
• The response need not make an explicit decision about the null hypothesis (reject
or fail to reject
)
in order to satisfy component 1. However, if an incorrect decision is stated, then component 1 is not
satisfied.
• If the conclusion and justification are consistent with an incorrect p-value (or an incorrect value of the test
statistic, or an incorrect confidence interval), the response may satisfy component 1 and component 2.
• If the response omits hypotheses, assume the correct alternative hypothesis,
a
H :
was provided
when scoring component 1 and component 2.
• If the conclusion includes a definitive statement (e.g., “this proves that we do not have enough evidence to
claim...” or “there is no evidence…”), then component 2 is not satisfied.
• If the response includes a statement that is equivalent to accepting the null hypothesis (e.g., “we conclude
th
at
t
he
proport
ion
of cu
st
omer
s wh
o wi
ll
place
an
order
is
0.40”)
, th
en
com
pone
nt
2 is not satisfied. • If the response includes an incorrect interpretation of the p-value, then the score for Section 3 is lowered
one level (that is, from E to P or from P to I).
• The clarity and quality of the statement of the conclusion and the statement of the justification may be
used in a holistic approach to decide whether to score up or down (e.g., raising a score of 2.5 to 3 or
reducing a score of 2.5 to 2).
Confidence Interval Approach:
• If the alternative hypothesis is specified correctly as
a
H :
then component 1 is satisfied if the
justification is based on whether 0.40 is below the lower end of the confidence interval. If the alternative
hypothesis is stated in the wrong direction, then component 1 is satisfied if the justification is based on
whether 0.40 is above the upper end of the confidence interval.