One of the biggest reasons we love the AP Statistics Exam is that you never quite know what is going to show up (especially on the Investigative Task!). But there is one question you can always expect to see:
A SIGNIFICANCE TEST!
Every year. Since the the first exam in 1997. And in the many years since the first exam, the rubrics used to grade these significance tests have been very consistent. Until now. The 2019 AP Statistics Exam rubric for question #4 revealed some big changes.
1. The significance test is now graded in 3 sections
In the past, the rubrics for significance tests were always graded in 4 sections (which makes sense because they are graded out of 4 points total). The 2019 rubric shows that they will be graded in 3 sections (changes are in bold)
Identify parameters as proportions
Clearly define parameters in context
Identify test by name or formula
Compare P-value to alpha
Correct conclusion consistent with the alternative hypothesis
Conclusion is in context
By grading the significance test in 3 sections, this opens up the opportunity for the College Board to ask a follow up question after the significance test. Check this post for some potential follow up questions that you might see.
2. Clearly define parameters in context (contextual subscripts are not enough!)
In the past, using a contextual subscript p(sub14) was sufficient for identifying parameters. No longer! In the 2019 rubric, the College Board is making it clear that these parameters must be defined in words. So here is what is expected:
Let p(sub14) represent the proportion of the population of kochia plants in the western United States that were resistant to glyphosate in 2014
3. 10% condition
While I teach this condition to my students every year, I always reveal at the end of the year that they won't need this for the AP Exam...and most for them stop writing it! Bummer for my 2019 students. So from here forward, if the context shows sampling without replacement, students should be checking the 10% condition.
it is reasonable to assume that the sample sizes are less than 10 percent of the respective population sizes.
Is it fair that College Board abruptly made these changes?
So some might say that it was quite rude of the College Board to drop these new changes without any heads-up. The reality is that they did this in a very fair way. They designed this particular rubric such that a student who didn't contextually define parameters or check the 10% condition could still get full credit.
Section 1 is scored Essentially correct (E) if the response satisfies components 1 and 4 AND at least one of the remaining components:
Section 2 is scored Essentially correct (E) if the response satisfies components 1 and 2 AND at least two of the remaining components:
Moving forward, I don't believe these rubrics will be written "softly" like this one. All of the components will be required for full credit. So start training your students NOW!