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 Rē notation. An Rē
value
of
0.0 indicates no relationship between variables, while a Rē 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 Rē 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).
