Causal Analysis/Diagnosis Decision Information System (CADDIS)

Step 5: Identify Probable Cause

• 5.1. Overview
   
• 5.2. Weigh Evidence
  for Each Cause 
• 5.3. Compare Evidence
  Among Causes
• 5.4. Complete Causal
  Analysis 

5.2.1. Consistency of Evidence

Concept
Confidence in the argument for or against a candidate cause is increased when many types of evidence consistently support or weaken it.

Table 5.6. Consistency of Evidence. A candidate cause is strongly supported if all available types of evidence are consistently supportive. It is greatly weakened if all available types of evidence are consistently weakening. It is weakened if some types of evidence support and others weaken the candidate cause.

Examples
Consider increased water temperature as a candidate cause of reduced abundance of fish. What findings support or weaken the case for increased temperature as the cause, in terms of consistency of evidence?

• Supporting evidence - Seven types of evidence were available and all support the case for increased temperature as the cause; no evidence weakens the case.
• Weakening evidence - Four types of evidence support the case for increased temperature, but 3 types of evidence weakened it.

How do I analyze consistency?
After assembling all the scored types of evidence for a candidate cause, observe if all types of evidence are supporting, weakening, or a mixture of points that support and weaken the case for the candidate cause. Ambiguous evidence (scores of 0) are not included. Based on this assessment, score the body of evidence for that candidate. Keep in mind that is not appropriate to add the plus and minus symbols from the scoring tables to determine consistency.

• Example analysis worksheets for consistency of evidence:
  • Little Scioto River, OH, USA
    • Decreased % Mayflies and Increased % Tolerant Macroinvertebrates
    • Increased % DELT
    • Increased Relative Weight

What evidence would support or weaken the case for a candidate cause, in terms of consistency?
Supports

• All types of evidence support the case for the candidate cause

Weakens

• All types of evidence weaken the case for the candidate cause
• Some types of evidence support and some weaken the case for the candidate cause, thereby undermining confidence in it as a true cause

How do I score the consistency of evidence?

Helpful tips

• The influence of consistency increases as more types of evidence are used.