Q&A #3699

Scatter plots

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From: Pat Ballew (for Teacher2Teacher Service)
Date: Apr 17, 2000 at 01:33:49
Subject: Re: Scatter plots

First, a really good site to learn from, and then some notes about general


This is a great site for statistical ideas, but it may be a little too deep
in some spots for an eighth grader. But maybe if you went through the tough
spots with her she could get most of the big ideas.

Second, I do not know if they are using the words in the same way in middle
school, but in general, if both things get bigger together we call that
"positive" correlation, and the line should go up from the bottom left to
upper right on the graph... Temp and heating costs would probably be a
negative correlation because as one (temp) got lower the other (heating cost)
gets higher.   correlation is measured as a number from -1 to +1... The
closer the value is to one, the more the points on the graph lie in a
straight line, the + and - is  just whether it is positive or negative

Points that lie in a perfect line have correlation of 1 or -1. Points that
seem to be like a cloud with no line in them have correlation near zero.
  Just another note, you can have a definite pattern, like a curve, but still
have a correlation near zero, because correlation is about fitting a LINE,
not something else.
  I am not sure how much of this the teacher wants them to know about this,
but the web page will give some nice examples. Good luck

 -Pat Ballew, for the Teacher2Teacher service

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