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CAHSEE Math 5.2 Statistics, Data, and Probability II 173 Views


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Statistics, Data, and Probability II Drill 5 Problem 2. Based on this data, a student who had missed 10 days of school can expect his GPA to be about what?

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Transcript

00:03

Here’s your shmoop du jour...

00:05

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

00:10

that more time spent in school means better grades.

00:15

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

00:21

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

00:25

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

00:30

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

00:37

And here are the potential answers...

00:42

OK, so this question is testing whether we

00:44

know the difference between positive and negative correlations.

00:48

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

00:54

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

01:00

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

01:03

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

01:09

How much are they alike?

01:10

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

01:15

a pretty clear NEGATIVE correlation.

01:17

That is – more absences means lower grades.

01:21

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

01:26

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

01:30

The answer is B.

01:32

As in… “Brains don’t work that way.”

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