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CADDIS Volume 1

Step 4. Evaluate Data from Elsewhere

Figure 4-1. Illustrates where Step 4, Evaluate Data from Elsewhere" fits into the Stressor Identification process.Figure 4-1. Illustration showing where Step 4: Evaluate Data from Elsewhere fits into the Stressor Identification process.

In Step 3, you examined and scored data from the case, eliminating candidate causes from further consideration 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 observations from case sites. These data may include information from other regional sites, or stressor-response relationships derived from field or laboratory studies. They may also include studies of similar situations and other kinds of information. After assembling information, it must then be related to observations from the case.

Questions that Frequently can be Addressed Using Data From Elsewhere

  • 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 Using Data From Elsewhere

  • 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. You cannot use evidence developed using data from elsewhere to eliminate a particular candidate cause; this evidence is used only to compare the weight of evidence associated with each cause.

Once the evidence from Step 4 has been scored, you combine it with the evidence from the case in Step 5, Identify Probable Causes.

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In-Depth Look

Virtually everything that is known about an impaired aquatic ecosystem and the candidate causes of the impairment may be useful for inferring causality. In this step, the investigation is widened by seeking data from outside of the immediate case and analyzing it to generate causal evidence. That evidence is combined with evidence from the case (Step 3), and all the evidence is evaluated and summarized in tables for strength-of-evidence analysis (Step 5).

Assembling the Data

Evidence from Step 4 relies on associations developed from data from elsewhere. Then, observations from the site are evaluated with respect to the associations developed from data from elsewhere. Sources of data from elsewhere include information from literature, observations from similar cases, or data sets from one or more larger geographic areas, such as a state or region.

Among the most commonly available and useful types of evidence are stressor-response relationships developed in the laboratory or from other field investigations. Although stressor-response relationships for chemicals are most familiar, the same concepts can be applied to other agents, such as sediment, flow, and temperature.

Volume 2: Sources, Stressors, and Responses describes available reviews of stressor-response relationships for metals and sediments. Stressor-response relationships also are provided in the Metals Chronic Concentration-Response Gallery and the Metals Species Sensitivity Distribution Gallery.

As stated in Step 3, evaluating the quality of data that have been collected and developed by others presents its own challenges. Although the collection and analysis procedures may have already been set and completed, you still have the responsibility of evaluating whether the data are of sufficient quality to support the current causal analysis prior to analyzing associations.

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Analyzing Associations

As in Step 3, data from elsewhere are analyzed in terms of associations that might support or weaken candidate causes. The types of evidence generated from these associations are described in Table 4-1 on this page.

Data compiled from the literature or from regional surveys usually require analyses to produce stressor-response relationships or other associations used for causal analysis. Volume 4: Data Analysis provides further details regarding these analyses.

If you have listed multiple stressors as a candidate cause, the analyses of data from elsewhere should be based on those aggregate causes. For example, if all divalent metals or all polycyclic aromatic hydrocarbons have been combined using a concentration additivity model, then all analyses of associations of that cause with effects should be performed using the sums of toxic units rather than the individual concentrations. This requires that the same method of combining the stressors be applied to both the data from the case and the laboratory or field data from elsewhere.

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Types of Evidence that Use Data From Elsewhere

The types of evidence that use data from elsewhere are listed below. The links lead to pages with descriptions and analytical advice. Each piece of evidence should be associated with only one type of evidence, to avoid double counting.

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Using the Evidence to Evaluate Candidate Causes

As in Step 3, the associations are evaluated by considering the degree to which they support or weaken the case for a candidate cause. We recommend scoring the evidence using a standard system. These scores are described in each type of evidence's information page, and are compiled in the summary table of scores.

After all available evidence has been evaluated, the degree to which the case for each candidate is supported or weakened is summarized.

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Results and Next Steps

At the conclusion of Step 4, the evidence from elsewhere is summarized and you should have two products: