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CG50: How to Work with Bivariate Data

CG50: How to Work with Bivariate Data

In this tutorial we're looking at how to plot scatter diagrams and how to calculate the correlation coefficient of the coefficients and the regression line. The dataset here is the number of goals scored and the number of points for teams in the Premiership in a season. You may find it easiest to reset your calculator before starting so that your screen matches the one in the video.

To type the data into lists one and two, choose stats mode. Type the x values first, the execute between each numbers and then when you've typed all the x values, move the cursor to the right. It jumps to the beginning of list two, ready for the y numbers. Make sure that the values pair up as you go. To graph the data, choose graph and go to set and select the type of graph and which lists to use for the graph.

The default settings give graph one and a scatter diagram. Use List one for the x and list two for the y values. Press graph one to draw the scatter diagram. The shape of this scatter diagram, gives a good idea that linear regression is appropriate for this data set. Use calc and F2 is the option for linear regression. I'm using the a plus bx as the equation for the regression line. Choose draw and return to the graph with the regression line added. To check the values of A and B, reselect a plus bx and the display shows the value for a and b, from which you can write down the equation of the regression line. I've rounded each value to three significant figures.

Should you need them, you can also see the value of the correlation coefficient, the coefficient of determination and the mean square error. The video tutorial on how to draw histograms uses the same data as this video. So if you go there next, you won't have to retype the data. Alternatively, you could save these lists to be used on another occasion.

You can find this tutorial and other tutorials on drawing boxplots etc at education.casio.co.uk