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Examining the Evidence

Bias and Ethics

Weighing the Evidence > Bias and Ethics
We’ve learned more about the influence of bias in people’s judgment. …it can operate at a subconscious level and that is an important consideration.

The Effects Of Bias

Everyone is susceptible to bias – the predisposition to decide something in a certain way. Biases can be planted and strongly reinforced through a person’s upbringing, culture, education, occupation, or other life experience.

In the context of forensic science and courtroom testimony, bias can present problems to the accurate adjudication of justice. Because all forensic evidence is subject to examination by a human who inevitably holds certain biases, conclusions can be altered by the bias, consciously or not.

The issue then becomes how to recognize when bias has affected a process, and how to minimize or eliminate the impact of bias.

Two Types Of Biases

There are two categories of biases: motivational and cognitive. When reviewing lab results, attorneys might want to be aware of how these biases can influence analysts’ interpretation of forensic evidence.

Motivational Bias

As the name implies, a motivational bias is a generally conscious (though probably not intentional) tendency to favor a particular party, for self-serving or personal motivations. For example, analysts who work directly under the prosecutor’s office or work closely with law enforcement personnel, may allow their relationships to sway their results.

Cognitive Bias

On a more unconscious level, cognitive bias occurs when people tend to see what they expect to see. This distortion of a person’s perception or thought process can affect decision-making, having an influence on the findings of a forensic expert.

Types Of Cognitive Bias

The umbrella term of cognitive bias encompasses a variety of specific biases, including:

Contextual Bias

This occurs when the decision of a person is influenced by extraneous (often ambiguous) information, that is not needed to draw the conclusion. For example, a fingerprint examiner who receives a file containing prints and a case summary (suggesting the suspect is the actual perpetrator), may be more likely to find that the prints match, than an analyst who receives no case information.

Confirmation Bias

This is the tendency of decision makers to give more weight to evidence that favors (confirms) their hypothesis, and ignore, excuse, or devalue evidence that contradicts it.

Selection Bias

This is when a type of statistical bias occurs, in which an analyst fails to make the right decision in selecting a person or sample from a greater population. This erodes the analyst’s statistical conclusions by destroying the assumption of random sampling. For example, at the crime scene an investigator only collects evidence that he personally feels is pertinent, potentially leaving out key evidence.

Expectation Bias

This is the result of a person prematurely coming to a conclusion without having first examined all available evidence, or conducting a thorough examination. An example would be when during arson investigations, examiners come to conclusions based on eyewitness accounts before fully inspecting the crime scene.

Though biases can never be eliminated, they can however be mitigated and acknowledged during the analysis and presentation of evidence. Learn about limiting bias in the next section.