ShmoopTube

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Here’s your shmoop du jour...

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Edgar, student at Duh University, has made a shocking, controversial claim –

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that more time spent in school means better grades.

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He may just be a student by day, but by night… Edgar is… CAPTAIN OBVIOUS!

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Anyway, he conducted a survey asking students about the number of days that they were absent

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in a semester, and their semester GPAs were. The results are shown in the plot below. 

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Based on this, a student who had missed 10 days of school can expect his GPA to be about…what?

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And here are the potential answers...

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OK, so this question is testing whether we

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know the difference between positive and negative correlations.

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The basic idea is that if elements are positively correlated, they generally head in the same direction.

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So... given NO OTHER DATA, if we just looked at this scatter plot of points, we’d surmise

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that they generally drift south as we move to the right.

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There is a clear ‘directionality’ to them. So we've got absences on one side and GPA on the other.

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How much are they alike?

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As we get higher in absences we have a LOWER grade point average – so in this case it’s

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a pretty clear NEGATIVE correlation.

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That is – more absences means lower grades.

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If it had been more absences means HIGHER grades, we’d have the dots gradually sloping

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UP instead of down… …and we’d have a whole lot fewer kids in school.

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The answer is B.

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As in… “Brains don’t work that way.”

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