University of Vermont

Kelley (1989)


Adding a Trend line

1.  Now that you have a graph the next step is to add a "best fit" line to your data, in order to determine the relationship between shell thickness and stratigraphic elevation (time).   In order to "fit" a line to your data you must first select Chart from the menu bar, and scroll down and select "Add Trend line". 

adding a trendline

2.  Once in the "Add Trundling" box select the "Linear" option,  because the data on your graph displays a linear trend.  A linear trend is defined as a statistical tendency for a pattern to drift in one direction, which is tested by fitting the line to the linear regression and determining an R value. 

Step 5F

3.  Linear regressions produce a "best fit line" for data values, and the "fit" to this line is given a value between 0.0 and 1.0.  The "fit" of a linear regression is identified by the R² notation.  An R² value of  0.0 indicates no relationship between variables, while a R² value of 1.0 indicates a strong relationship between the variables.  To turn on the R² value for your graph click on the Options tab in the "Add Trend line" box and check the boxes entitled "Display equation on chart", and "Display R-squared value on chart".

equasion and R vale

4.  Once the boxes have been check click on the "OK" button and the chart will appear with your equation and R² value displayed.

Graph with trendline

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Last modified October 02 2008 04:06 PM

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