In Step 3, you examined and scored data from the case, eliminating candidate causes from further consideration where possible, and diagnosing causes using symptoms when possible. The candidate causes that remain are evaluated further in Step 4, by bringing in data from studies conducted outside of the case. The evidence developed from this information completes the body of evidence used to identify the most probable causes of the observed biological effects.

The key distinction between data from elsewhere and data from the case is location: data from elsewhere are independent of what is observed at the case sites. Data from elsewhere may include information from other sites within the region; stressor-response relationships derived from field or laboratory studies; studies of similar situations in other streams, and numerous other kinds of information. After assembling the information, it must then be related to observations from the case.

Data from elsewhere can be used to address the following questions:

Questions that frequently can be addressed:

• Is it plausible that the candidate cause resulted in the observed biological effect, given stressor-response relationships derived in the laboratory?
• Is it plausible that the candidate cause resulted in the observed biological effect, given stressor-response relationships derived from other field studies?
• Is the pathway linking the candidate cause to the observed effect mechanistically plausible?

Questions that less frequently can be addressed:

• Are there other cases in which the biological effect responded to manipulation of the candidate cause?
• Is it plausible that the candidate cause resulted in the observed biological effect, given stressor-response relationships derived from simulation models?
• Do analogous stressors cause similar effects?

As in Step 3, each type of evidence is evaluated and the analysis and results are documented in a series of worksheets. You cannot use evidence developed using data from elsewhere to eliminate a particular candidate cause; this evidence is used only to compare the strength of evidence associated with each cause. Once the data from elsewhere have been scored, you combine it with the evidence from the case in Step 5, Identify Probable Causes.