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Identifying the probable cause

Identifying the probable cause. Detect or Suspect Biological Impairment. Stressor Identification. Define the Case. List Candidate Causes. Decision-maker and Stakeholder Involvement. As Necessary: Acquire Data, and Iterate Process. Evaluate Data from the Case.

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Identifying the probable cause

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  1. Identifying the probable cause

  2. Detect or Suspect Biological Impairment Stressor Identification Define the Case List Candidate Causes Decision-maker and Stakeholder Involvement As Necessary: Acquire Data, and Iterate Process Evaluate Data from the Case Evaluate Data from Elsewhere Identify Probable Cause Identify and Apportion Sources Management Action: Eliminate or Control Sources, Monitor Results Biological Condition Restored or Protected

  3. How we identify probable causes • Eliminate when you can • Diagnose when you can • Otherwise, analyze strength of evidence HOW? Apply a scoring system to the available evidence under each type of evidence

  4. R refutes D diagnoses +++ convincingly supports (or weakens - - -) ++ strongly supports (or weakens - -) + somewhat supports (or weakens - ) 0 neither supports nor weakens NE no evidence The scoring system

  5. What you are looking for spatial/temporal co-occurrence

  6. Why score this way

  7. Scoring of laboratory tests of site media Scoring of stressor-response from other field studies

  8. Example: strength of evidence analysis

  9. Weighing the evidence for each candidate cause • Evaluate the quantity & quality of evidence • Evaluate consistency, patterns, strength, & credibility • Summarize the compelling evidence

  10. Evaluate quantity & quality of evidence • Quality & quantity of data influence scores • Now evaluate overall quality of evidence • Lots of consistent evidence reduces quality concerns for any 1 line of evidence • Poor quality data may be discounted • Consider study designs, methods, relevance, variability, & other QA issues

  11. Evaluate consistency, patterns, strength, & credibility • Prepare summary table of scores • Do not add up scores! • Evaluate consistency of evidence • Look for compelling evidence • If evidence is inconsistent, consider mechanistic explanations • e.g., lab data not consistent with field conditions due to differing bioavailability

  12. Scoring consistency & credibility

  13. Summarize compelling evidence • Make an overall evaluation of strength of evidence for each candidate cause • what evidence compels belief that candidate cause induced effect? • what evidence strongly casts doubt? • Consider the principle characteristics of causal relationships • these are what you’re trying to show • they summarize the 15 types of evidence

  14. Characteristics of Causal Relationships

  15. There is no magic formula… • All candidate causes must be compared to determine: • if there is more than 1 probable cause • the level of confidence in the results

  16. …celebrate, then remediate for Candidate Cause 1 Comparing evidence among causes: best-case scenario You have compelling evidence for 1 candidate cause; others are weak or refuted...

  17. Strong evidence for one candidate cause may be sufficient • Consider if weakness is due to lack of data Comparing evidence among causes: more (likely) scenarios You have uneven evidence across candidate causes...

  18. Reconsider the impairment • Consider additional candidate causes • Consider gathering more data • Consider episodic events • Apply professional judgment to identify most likely cause You have unsatisfying evidence across all candidate causes…

  19. Consider disaggregating indices or metrics • Combine causes if they share causal pathways, modes of action, sources and routes of exposure, or if they interact • Remediate dominant cause • Design remediation to address multiple causes You have evidence suggesting multiple causes…

  20. Gather data if possible • Consider other bases for remediation (e.g., BMPs, chemical criteria) and monitor biological responses • Use professional judgment as last resort You have insufficient data…

  21. How do I communicate results? • Make your logic clear • Present the critical evidence • Reveal uncertainties • Fit communication to your audience • For technical reviewers, include text & tables • For decision makers, may be helpful to use annotated conceptual model

  22. industrial facility industrial facility dairy farm subdivision POTW dams DO higher at impaired site vs. reference after rerouting industrial discharge had decreased concentrations of Zn & other toxics, increased EPT taxa richness ↓ EPT richness ↓ trout abundance NH3 higher at impaired site vs. reference, but not at levels sufficient to cause impairment Example: using models for communication ↑ other toxics ↑ NH3 ↓ dissolved oxygen ↑ Zn ↑ temperature

  23. What comes after causal analysis? • If confidence in results is low… • plan studies to obtain critical evidence • experimental studies most likely to be convincing • If confidence in results is high… • identify sources • take action • monitor results

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