Why is the scatter plot of quiz scores not linear?

[lLovePhysics]

I have trouble figuring out a data problem. Please take your time to help me out. Thanks in advance!

1. The ordered pairs represent the scores on two consecutive 15 point quizzes for a class of 18 students. (data provided) Why is the graph not linear?

My solution: They provided me data and when I graphed them they were not linear but in fact like a "blob". Are the data not linear because everyone has different scores?

 

[Feldoh]

I think it's like (test 1,test 2) for 18 different students. If your getting a "blob" (no correlation) it would be because that the students are not receiving the same scores on both of their tests, and also because the students are not scoring the same scores as their classmates.

 

[Integral]

Why would you expect a linear relationship between the 2 tests? Each is an independent event. Some will get similar scores, others will do better on one then the other. There is no single rule linking the 2 tests.

 

[lLovePhysics]

Yeah it's kind of a weird question to ask...

 

[EnumaElish]

I have trouble figuring out a data problem. Please take your time to help me out. Thanks in advance!

1. The ordered pairs represent the scores on two consecutive 15 point quizzes for a class of 18 students. (data provided) Why is the graph not linear?

My solution: They provided me data and when I graphed them they were not linear but in fact like a "blob". Are the data not linear because everyone has different scores?

The only circumstance in which you would observe a line (through the origin) is when X and Y are perfectly positively correlated; that is Corr(X,Y) = +1.