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Regression: Tree Rings and Measuring Things

Author(s): Greg Wiggins1, Suzanne Lenhart2

1. Department of Mathematics, University of Tennessee, Knoxville 2. University of Tennessee

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Students develop scatter plots of growth rings by tree diameters and determine the equation of their best fit line.

Licensed under CC Attribution-ShareAlike 4.0 International according to these terms

Version 1.0 - published on 03 Apr 2021 doi:10.25334/C4R8-ZN66 - cite this


Assemble students in groups of 2‐3 with a calculator and ruler for each group. Using the sheet ‘Example: Regression’ have the students examine the scatter plot of growth rings by tree diameter. Have the students consult and draw an approximate best linear fit line through the points. Have them compare the position of the line, the y‐intercept, and the nearest (x, y) coordinates to those in the associated ‘Calculations’ section. How well did they approximate the line?

Next, explain they will be measuring biological data and calculating variables to exactly determine the mean x and y coordinates, slope, and y‐intercept. To compare their calculations to their estimation skills, have the students measure the diameter and count the growth rings of the sample trees on the ‘Regression Exercise’ sheet, entering the data into the table provided. Next have students plot the data. Then have the students calculate the mean of the x data and the mean of the y data. Have the students draw their own line of the best fit.

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