To choose between hypotheses diagnostic evidence is needed. In determining the diagnosticity of evidence taking account base rates is a requirement: for example, there may be more patients with chest infections who cough than patients with lung cancer who cough, but that may be because, overall, there are more patients with chest infections. The number of patients with the disease who do not cough also has relevance in deciding whether coughing is a useful symptom for distinguishing patients with the two diseases.

For example:

Concern and alarm starts building within a particular (largely) temporary-resident university student community in City X, let’s refer to this community as Ionian, over the belief that they are being targeted for and the subject of race crimes. Part of the police response is to indicate that there are certainly members of the Ionian community who have been bashed and robbed over recent months, but that their group is not overrepresented as victims of such attacks, and that while there are from time to time some incidents with indications of racial overtones against various ethnic, national, and racial groups there is no good evidence at present of a cluster of hate crimes against members of the Ionian community, especially foreign students. An incident is later reported to Ionian community leaders that several Ionian students have been threatened and racially taunted by males of “middle-eastern” appearance, then set upon – one of the students is unable to escape and is assaulted, fortunately not seriously, and left lying bleeding and bruised in the gutter – later that day three “middle-eastern-looking” members of another community group are physically abused in an apparent retaliatory episode.

Is this latest incident against the Ionian youths diagnostic of an hypothesis of racist attacks being perpetrated against the Ionian community? The short answer is that it is pseudo-diagnostic. The nature and quality of the information is such as to be unable to offer us a meaningful answer as to the overall hypothesis at issue, even if the specific incident was racially-motivated. It almost certainly will harden the pre-existing belief of those who already ‘know’ the answer. Provided the crime statistics utilized by the police have good reliability, are interpreted correctly, etc., they can help discriminate between hypotheses. Sadly, as a result of the “media frenzy” which accompanies such matters – in a kind of self-fulfilling prophesy – hate crime acts may actually increase, at least in the short term.

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Glossary of selected Judgement & Decision-making, Belief-related, and other Psychology terms A-Z »