5 I. Observer Effects and Examiner Bias Chisum and Turvey quote Paul L. Kirk, who was a pioneering criminalist, about the interpretation of evidence, “Physical evidence cannot be wrong, it cannot be perjured, it cannot be wholly absent. Only in its interpretation can there be error.” (Chisum, p. 51). This becomes a real issue because a great deal of the evidence we deal with can be interpreted in various ways depending on a number of subjective influences. A. Observer Effects – Observer effects can be both conscious and subconscious. Both conscious and subconscious needs and expectations shape both our perception of facts and their interpretation. It can affect what is recognized as evidence, what is collected, what is examined, and how it is interpreted. At its most basic, an observer effect is a psychological bias or effect on the observer’s part that distorts how the evidence is recognized, collect, examined, or interpreted. It is often subconscious (below the level of awareness) on the part of the observer and may significantly affect the reconstruction of the crime. We all have them and the question thus becomes, not whether I have them, but how do I guard against them and eliminate their influence on my reconstruction. B. Potential Observer Effects 1. Ambiguity and Subjectivity – Ambiguity is a factor when evidence or circumstances are incomplete, murky, or equivocal. Subjectivity is a factor when identifications and interpretations rest on the examiner’s experiences or beliefs. They become problematic when the examiner or investigator believes that his experience is all that is required to render an identification. There are at least three areas in reconstruction where subjectivity can show up: 1) evidence collection; 2) evidence quantity and quality; 3) lack of standards for qualifying the results of comparative analysis and identification (Chisum, p. 59). The occurrence of ambiguous physical evidence as well as evidence that is susceptible to subjective interpretation opens the way for subconscious observer effects to affect the results you obtain. 2. Lure of Expectation – We as investigators are often put in situations where we have access to information that can give rise to conscious or unconscious expectations. One of the most common expectations of this type is that the subject must be guilty of something even if they are not guilty of the crime of which they are accused. I once had another officer tell me (in reference to a real thug/scumbag that was a suspect in a homicide) that even if he had not done the crime, to charge him would not be a great miscarriage of justice. We work in a pro-prosecution environment where the suspect’s guilt is suspected and anticipated and this may lead to subconsciously developing pre-examination expectations that may influence the results (Chisum, p. 60). 3. Single Sample Testing – Evidence that is turned over to forensic examiners tends to fall into one of three catetor.