Question

18. The method detection limit for GC/MS analysis of atrazine is typically near 0.010 ppb while the ELISA test describes its sensitivity as the “least detectable dose” (LLD) of 0.05 ppb of atrazine in water. Based on this comparison one would think that the ELISA test is suitable for monitoring part per billion levels of atrazine in surface water. In the example above, can you think of some reasons (at least 2) why the results are not identical? Does each method have the same probability of producing a Type I or Type II error?

Answer 1

Why the results are not identical?

1. ELISA detections of atrazine are likely to include some cross-reactant compounds and thus it ends up overestimating

2. ELISA method may have detected structurally similar metabolites or compounds during the degradation study

ELISA has a higher probability of Type 1 (False positive) as it can detect cross-reactants and structurally similar metabolites or compounds as Atrazine

Type 2 (False negative) error would be the same in both the methods because if something cannot be detected by GC as atrazine it would not be detected by ELISA too.

False Positive

A false positive is where you receive a positive result for a test when you should have received a negative result. It’s sometimes called a “false alarm” or “false positive error.”

False Negative

A related concept is a false negative, where you receive a negative result when you should have received a positive one. For example, a pregnancy test may come back negative even though you are in fact pregnant.