We compared the performance of Test Site Analysis (TSA) to 2 existing bioassessment methods: the BEnthic Assessment of SedimenT (BEAST), and the multimetric approach. In TSA, simple spreadsheet calculations are used to: 1) derive an overall multivariate measure of dissimilarity between a potentially impaired test site and a reference benchmark using a number of biological summary metrics, 2) classify each site as impaired, potentially impaired, or in reference condition with formal hypothesis tests, and 3) identify the metrics important in distinguishing a significantly impaired test site from the reference benchmark. We used data collected as part of the Fraser River Action Plan (British Columbia, Canada) to compare the biological condition of 15 potentially impaired test sites known to be exposed to agriculture, logging, or mining to the condition of 61 minimally disturbed reference sites with comparable habitat. When TSA was used, the false-positive (i.e., Type-1 error) and false-negative (i.e., Type-2 error) rates were as low as or lower than when the other methods were used. Using TSA enhances our ability to identify impairments because it accounts for correlations among metrics and uses a statistically defined potentially impaired category. TSA integrates formal hypothesis testing with the strengths of many existing approaches, does not require specialized software, and enhances our ability to detect and diagnose biological impairments.