Date: Jun 24, 2011 12:43 AM
Author: Josh Tabor
Subject: RE: [ap-stat] Things I learned from the 2011 AP Statstics reading

Hi Dennis-



I agree that the tense of the conclusion is not the most important thing-it
is certainly possible to have a correct conclusion in the past tense.



Here are some examples:



* If a presidential approval poll was done in August 2009 and we
constructed a CI for the president's approval rating, it would be wrong to
make a generalization about "the proportion of US adults who said they
approved of the president's performance in August 2009" because this is
clearly referring to the sample.



* A better, but somewhat ambiguous conclusion would be about the
"proportion of US adults who approved of the president's performance in
August 2009." In this case, it is unclear if the group that "approved" is
the sample or the population. Saying "all US adults" would make this much
better, even in past tense.



* A better conclusion would be about "the proportion of all US
adults who would have said "approve" had they been asked about the
president's job performance in August 2009."



My point in the original email was that when a conclusion/interpretation is
in the past tense, this is often a clue that the student might be
misunderstanding the difference between the statistic and the parameter.
But, you are right that the most important thing is to clearly identify the
population/parameter regardless of the tense.



Josh





_____

From: Dennis Roberts [mailto:dmr@psu.edu]
Sent: Wednesday, June 22, 2011 6:35 AM
To: AP Statistics
Subject: RE: [ap-stat] Things I learned from the 2011 AP Statstics reading



At 01:05 AM 6/22/2011, Josh Tabor wrote:



Hello All-
Notice that the tense of the verb is no longer in the past tense. While I
am sure there are exceptions to this rule, I suggest to my students that
interpretations/conclusions should never be in past tense because this often
means that the student is referring to the data from the study rather than
what they are trying to make an inference about.


Not to toss hmmms into this discussion but ... since the CI is based on data
from a sample that already exists ... then the conclusion would seem to be
about the overall population that existed when these data were collected.
This is not a future sample ... on which we can say things about a
population in the future ... it's about a sample now ... or in the past ..
and it's associated population.

In a very real sense, the CI is about a past tense.

I don't think I would be worrying about the tense of the verb rather, I
would be wanting to make sure that the student refers to the population from
which this sample was taken.

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