Using impact simulations to evaluate the power of Skeena Reference Condition Approach stream bioassessments

Abstract

Effective use of bioassessments requires an understanding of their performance. This study evaluated the performance of Skeena Reference Condition Approach (RCA) bioassessments by calculating Type I and Type II error rates and power using a data set of artificially-impacted test sites. Results from this study demonstrated that there are trade-offs between the two error types. Type I error rates – the chance of concluding that a site is impacted when it isn’t – were higher than expected based on decision points set in the assessments. Type II error rates – the chance of concluding that a site is not impacted when it is – were often even greater. To achieve sustainable development, resource managers who use Skeena bioassessments must carefully consider the risks associated with making errors, and may wish to set decision points that result in more Type I errors in order to reduce the likelihood of making costly Type II errors.