Very few assays reach the top level on the scale, but this doesn’t necessarily mean that they don’t work well. Care should be taken in basing management responses purely on the results of a semi-validated essay, particularly in regulatory contexts. However, there are times when a semi-validated assay can still be a useful tool to gain an idea of whether particular species may or may not be present – especially when used in combination with other survey methodologies (themselves often imperfect). What is critical is that the user understands the assay is not fully validated and bears this in mind when interpreting results. Therefore, for each level on the scale, we also present the remaining uncertainties that users should be aware of, as well as guidance on how a positive or negative result should be interpreted. Importantly, we also include a set of key assumptions about how the analyses have been conducted.