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How Does a Scatter Plot Help You Determine Whether or Not Two Variables Are Correlated?

By Marija Kero, eHow Presenter

Hi, my name is Marija. I'm a mathematician and today I'm going to show you how a scatter plot can help you determine whether or not two variables are correlated. So, I'm going to draw a few different scatter plots for you, and we're going to observe the relationship between the variables. If I have a scatter plot like this first one that I'm drawing, it's not going to be a perfect relationship, but I can tell that it looks like there's a positive slope to this line. So, if I estimated a trend line through this scatter plot, it would be something like that. And I see that that line clearly has a positive slope. So, this scatter plot would indicate that my variables have a positive correlation. So, this might be something like time spent studying, and this might be something like your grade on a test. And those two things would have a positive correlation. The more time spent studying, the higher the grade on a test. And it's not perfect, and yet it's clearly some sort of positive correlation. Now, a scatter plot that looks like this, again, it's not going to be a perfect correlation, but clearly I can draw an estimated trend line through here that's going to have a negative slope. So, this scatter plot shows me two variables that have a negative correlation. Now, if I have a scatter plot that looks like this one here, there doesn't seem to be any correlation. Because if I try to draw a trend line, I wouldn't know which way to go. There are some points at which, when this is high, when this variable has a high value, there is a low point. And when this variable has a high value, there's also a high point. So, this type of scatter plot would show no correlation between my variables, showing that neither of them is dependent on the other one. So, this would be a positive correlation, negative correlation, and no correlation scatter plot. My name is Marija, and I just showed you how a scatter plot can help you determine whether or not two variables are correlated.