Jump to main content or area navigation.

Contact Us

CADDIS Volume 1: Stressor Identification

Step 4: Evaluate Data from Elsewhere

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 (example stressor-response relationships). 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.

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.

Types of evidence that use data from elsewhere

The types of evidence that use data from elsewhere are conceptually described in Table 4-1 with links to more detailed descriptions and analytical advice. Each piece of evidence should be associated with only one type of evidence, to avoid double counting.

Table 4-1. Types of Evidence that Use Data from Elsewhere
Type of Evidence Definition
Stressor-Response Relationships from Other Field Studies The causal agent in the case is at levels that are associated with similar biological effects in other field studies.
Stressor-Response Relationships from Laboratory Studies The causal agent in the case is at levels that are associated with related effects in laboratory studies. The laboratory studies may test chemicals, materials, or contaminated media from sites contaminated by the same chemical, mixture or other agent as the case. If the effects or conditions in the laboratory and field are dissimilar, extrapolation models may improve the correspondence.
Stressor-Response Relationships from Ecological Simulation Models The causal agent in the case is at levels that are associated with similar effects in mathematical models that simulate ecological processes.
Mechanistically Plausible Cause The relationship between the causal agent and biological effect is consistent with known principles of biology, chemistry and physics and with properties of the affected organisms and the receiving environment.
Manipulation of Exposure at Other Sites At similarly affected sites, field experiments or management actions that alter exposure to a causal agent also alter the biological effects.
Analogous Stressors Evidence that agents that are similar to the candidate causal agent in the case cause effects similar to the effect observed in the case is supportive of that candidate causal agent as the cause.

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.

Top of page

Previous: Overview | Next: Results and Next Steps | Continue to Step 5 | Step-by-Step Guide Introduction

Jump to main content.