University of Vermont

Virtual Field Study


Graphing Data / Identifying Trends

    When the data for internal volume and shell thickness versus age was plotted, a trend in both features was observed over time.  A linear trend is defined as a statistical tendency for a pattern to change in one direction, the validity of which is tested by fitting the line to the trend.  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 idicates a one to one relationship between the variables.  It varies as a function of sample size, but R2  values above 0.7 are generally considered statistically robust.
    Data collected from Astarte and Anadara shells had an R² value for both variables of shell thickness and internal volume that ranged between 0.85 and 0.95.  This indicates that a strong positive relationship exists between these variables and their age (as measured by stratigraphic position).    
Combo Photograph
Click here if you would like to graph real data from this study.

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Last modified October 06 2008 03:17 PM

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