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Here’s your shmoop du jour: Edgar, student at Duh University, has made
a shocking, controversial claim – that more time spent in school means better grades.
He may just be a student by day, but by night… Edgar is… CAPTAIN OBVIOUS!
Anyway, he conducted a survey asking students about the number of days that they were absent
in a semester, and their semester GPAs. The results are shown in the plot below.
Based on this, a student who had missed 10 days of school can expect his GPA to be about…
what?
And here are the potential answers: OK so this question is testing whether we
know the difference between positive and negative correlations.
The basic idea is that if elements are positively correlated, they generally head in the same
direction.
So... given NO OTHER DATA, if we just looked at this scatter plot of points, we’d surmise
that they generally drift south as we move to the right.
There is a clear ‘directionality’ to them. And here the question asks about the correlation
of the number of absences and the GPA.
As we get higher in absences we have a LOWER grade point average – so in this case it’s
a pretty clear NEGATIVE correlation.
That is – more absences means lower grades.
If it had been more absences means HIGHER grades, we’d have the dots gradually sloping
UP instead of down…
…and we’d have a lot fewer kids in school.
Answer: B.
As in… “Brains don’t work that way.”