Identifying the probable cause

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

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

4 The scoring system R refutes D diagnoses +++convincingly supports (or weakens - - -) ++strongly supports (or weakens - -) + somewhat supports (or weakens - ) 0 neither supports nor weakens NEno evidence

5 What you are looking for spatial/temporal co-occurrence + The effect occurs where or when the candidate cause occurs, OR the effect does not occur where or when the candidate cause does not occur. 0 It is uncertain whether the candidate cause and the effect co-occur The effect does not occur where or when the candidate cause occurs, OR the effect occurs where or when the candidate cause does not occur. R The effect does not occur where and when the candidate cause occurs, OR the effect occurs where or when the candidate cause does not occur, and the evidence is indisputable.

6 Why score this way + This finding somewhat supports the case for the candidate cause, but is not strongly supportive because the association could be coincidental. 0 This finding neither supports nor weakens the case for the candidate cause, because the evidence is ambiguous This finding convincingly weakens the case for the candidate cause, because causes must co-occur with their effects. R This finding refutes the case for the candidate cause, because causes must co-occur with their effects.

7 no R Because laboratory tests do not exactly replicate toxic effects in the field. Scoring of laboratory tests of site media Scoring of stressor-response from other field studies no R Because there may be substantial and consistent differences in organisms or conditions between the case and elsewhere.

8 Willimantic case study MetalsNH 3 FlowSiltLow DO TempFoodEpisodic Mix Types of Evidence that Use Data from the Case Spatial/Temporal Co-Occurrence Evidence of Biological Mechanism Causal Pathway Stressor-Response from the Field Manipulation of Exposure Verified Predictions Types of Evidence that Use Data from Elsewhere Stressor-Response from Other Field - + Stressor-Response from Laboratory 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 Consistency of Evidence All available types of evidence support the case for the candidate cause All available types of evidence weaken the case for the candidate cause All available types of evidence support the case for the candidate cause, but few types are available. + All available types of evidence weaken the case for the candidate cause, but few types are available. - The evidence is ambiguous or inadequate.0 Some available types of evidence support and some weaken the case for the candidate cause. - Explanation of the Evidence There is a credible explanation for any negative inconsistencies or ambiguities in an otherwise positive body of evidence that could make the body of evidence consistently supporting. + There is no explanation for the inconsistencies or ambiguities in the evidence. 0 There is a credible explanation for any positive inconsistencies or ambiguities in an otherwise negative body of evidence that could make the body of evidence consistently weakening. -

13 Willimantic case study MetalsNH 3 FlowSiltLow DO TempFoodEpisodic Mix Types of Evidence that Use Data from the Case Spatial/Temporal Co-Occurrence Evidence of Biological Mechanism Causal Pathway Stressor-Response from the Field Manipulation of Co-occurrence Verified Predictions Types of Evidence that Use Data from Elsewhere Stressor-Response from Other Field - + Stressor-Response from Laboratory Evaluating Multiple Types of Evidence Consistency of Evidence

14 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

15 Physical Interaction Causal agents change an affected agent by physical interaction. DirectionalityThe cause precedes its effect Sufficiency Intensity or frequency of contact with the cause is adequate to produce observed effect Sequential Dependence All effects result from a prior sequence of cause-effect events Coherence of Characteristics Specific causal relationships are consistent with scientific theory Characteristics of Causal Relationships

16 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

17 Comparing evidence among causes: best-case scenario You have compelling evidence for 1 candidate cause; others are weak or refuted... TYPE OF EVIDENCE CANDIDATE CAUSE 123 A++-R B+-- C+- Consistency+- …celebrate, then remediate for Candidate Cause 1

18 Comparing evidence among causes: more (likely) scenarios You have uneven evidence across candidate causes... TYPE OF EVIDENCE CANDIDATE CAUSE 123 A++– B+– C++ Consistency+ – Strong evidence for one candidate cause may be sufficient Consider if weakness is due to lack of data

19 You have unsatisfying evidence across all candidate causes… TYPE OF EVIDENCE CANDIDATE CAUSE 123 A+– B–– C+ Consistency– – – Reconsider the impairment Consider additional candidate causes Consider gathering more data Consider episodic events Apply professional judgment to identify most likely cause

20 You have evidence suggesting multiple causes… TYPE OF EVIDENCE CANDIDATE CAUSE 123 A+++ + B+ + C + Consistency+ + + 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

21 You have insufficient data… TYPE OF EVIDENCE CANDIDATE CAUSE 123 ANE – B+ C Consistency000 Gather data if possible Consider other bases for remediation (e.g., BMPs, chemical criteria) and monitor biological responses Use professional judgment as last resort

22 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

23 ↑ other toxics Example: using models for communication ↓ dissolved oxygen ↑ temperature ↓ EPT richness ↓ trout abundance POTW industrial facility damssubdivisiondairy farm ↑ NH 3 ↑ Zn DO higher at impaired site vs. reference after rerouting industrial discharge had decreased concentrations of Zn & other toxics, increased EPT taxa richness NH 3 higher at impaired site vs. reference, but not at levels sufficient to cause impairment industrial facility

24 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