One goal of the analysis
was to identify whether there was a statistically significant difference in the number of species throughout the time period, and we
found there was with a 95% confidence interval. A polynomial contrast was used to detect linear and quadratic trends with time. An
exponential model was also used to analyze the same data. However, unlike the count model, the exponential model did not take
into consideration the difference in the number of catalogs used
in each time period. While the results indicated that both models fit the data, we chose to use the negative binomial regression
count model because it took into consideration the differences in
the number of catalogs used in each time period. We also found that
there were fifteen species offered consistently in every decade.