The first step in considering data from the case is to assemble relevant data. These data can include the following:

• Measurements of the biological response

  You should have identified the biological responses that will be analyzed in Step 1. Biological responses might include:

  • Brown trout abundance,
  • Ephemeroptera richness,
  • Periphyton biomass.
  
  
• Measurements of the proximate stressor

  In the most straightforward cases, measurements of the proximate stressor (also called the causal agent) itself are available, for example, degree of siltation, dissolved oxygen concentrations, or chemical concentrations. Obtaining measurements of the proximate stressor that can be associated with the effect can be challenging. In some cases, the candidate cause is the lack of a required resource, such as nesting habitat. In these cases, measurements can establish that the resource is indeed missing at the place and time it would be required by an organism.

• Measurements of factors from the causal pathway from source to proximate stressor

  For complex causal pathways, measurements along the pathway may be used to evaluate whether necessary steps are occurring or are missing. For example, one pathway by which excess nutrients affect stream biota is by stimulating periphyton growth, which decays and reduces dissolved oxygen. To evaluate this pathway, you could supplement data on dissolved oxygen concentrations with data on the other steps in the causal pathway (e.g., nutrient concentrations and periphyton biomass).
• Measurements of exposure or physiological mechanism

  These measurements are used to verify that biologically relevant exposure has taken place. Measurements might include biomarkers of exposure, tissue residues, or abundances of organisms representing different functional feeding groups.