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Depending on Each Other - Data Correlation with the fx-991CW

Writer's picture: Karen GreenhausKaren Greenhaus

I am going to end the statistical focus for these past few blog posts with a brief discussion and how-to on correlation - i.e. if 2 variates correlate, then if one increases, the other tends to increase or decrease linearly. Determining if one thing affects or depends on another is a question that is often asked when looking at data. For example, does the state of the economy impact the spending we are doing during this holiday season? Or, if I am a student, do the hours spent studying for math tests relate to the scores on those tests (i.e. if I study more, my scores will go up)? The ability to show a correlation, or connection between two sets of data helps in decision making for future trends, whether that relationship is a positive or negative one.


Very briefly, to determine if two sets of data have a correlation, or relationship, we use the correlation coefficient, calculated as follows:


The closer r is to 1, the stronger the positive correlation, the closer to -1, the stronger the negative correlation, and if r is close to 0, then there is a weak or no correlation. It looks something like this on a scatter plot:


Images & more information can be found in the attached PDF below.
Images & more information can be found in the attached PDF below.

As you can see from the images, if there is a positive or negative correlation, either strong or weak, the scatter plot seems to indicate a linear relationship, so being able to create a scatter plot from the data is one quick way to determine if there is a relationship. If there is, then you can use the correlation coefficient to determine more specifically the strength of that correlation.


The video below demonstrates how to use the fx-991CW scientific calculator to plot 2-variable data, find the 2-variable statistics, including the correlation coefficient, and then use the QR code capabilities to see the visual representation of the data, using the ClassPad.net dynamic workspace, in a scatter plot. And, if there is a relationship, to find the linear regression equation. 



For more detail and some practice problems around data correlation, be sure to download this PDF on Data Correlation. I have also included an extra resource for determining when to use a bar graph or a histogram when looking at data to continue to build understanding of data and using data visuals to make decisions.




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