Our lab delivers consistent results with lower false positives and better determinations of true toxicity than other labs nationally. And we have the data to prove it!
EPA DMR-QA Studies have been successfully completed by Coastal Bioanalysts, Inc. since 1991 (the first year toxicity data was included in the program), with 395 toxicity data points submitted to date. Results of the two most recent studies are available in the sidebar.
Accuracy does not apply to toxicity testing because absolute toxicity values are unknown. Consequently study acceptance values are based on the 95% probability limits of the mean for all reporting laboratories, including those that are experiencing problems during the mandatory testing period. Statistically, 5% of the values submitted by an in-control lab should fall out of the acceptance range; it is nearly impossible for all of a laboratory's values to fall within acceptance limits for this many data points. Our overall pass rate of 95.4% is statistically sound.
Also, it is well recognized that poor methods (inferior animal health, inadequate water quality, etc.) are more likely to increase toxicity (lower IC25 or LC50). Thus the true LC50 or IC25 value is probably somewhat higher than the mean study value. Typically LC50 and IC25 values for our lab are slightly above study values.
Reference toxicants are used to evaluate the overall health and sensitivity of the test organisms and the continuing ability of the laboratory to successfully perform the tests. Individual reference test results are compared to control charts to determine acceptability.
The coefficient of variation (CV) for the test LC50s (acute tests) or IC25s (chronic tests) provides a measure of test repeatability or precision; the lower the CV value the less variable the test results and the lower the frequency of false positive and false negative results. For WET testing EPA has compiled frequency distribution tables of intra-laboratory CVs for reference toxicant tests from a national data set. This allows laboratories to compare their test precision with that of other laboratories. Our CV values are consistently well below the national average and most are within the 10th or 25th percentile.
The EPA variability study scrutinized laboratory adherence to standard methods and evaluated test performance using a data set of validated results. Our laboratory (number 73) exhibited excellent performance, with test results in close agreement with other in-control labs. All blank samples were correctly identified as non-toxic by our laboratory. Additionally, data qualifiers (assigned by EPA) were essentially non-existent for our data compared with those of other labs.