## Kelley (1989)

stepfive

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".

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.

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".

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

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