Although it is traditional to calculate results of chronic toxicity tests using hypothesis testing to detect statistically significant differences from the control, calculation of results using regression analysis offers several major advantages. Regression analysis can directly produce a point estimate of the concentration causing any specified amount of adverse effect. In addition, whereas the degrees of freedom, precision of the test, and selection of have no impact on results calculated using regression analysis, they have a great impact on results calculated using hypothesis testing. Further, use of regression analysis emphasizes the necessity of considering the biological importance of the adverse effects observed in toxicity tests. By using hypothesis testing, aquatic toxicologists have been able to avoid this difficult, important question by presenting results in terms of a variable 'statistically significant difference'.