Abstract
AbstractWe obtain the input data for Bayes Theorem, and use the theorem to determine the probability of a patient having a lumbar HNP, given only a positive MRI. We also enumerate the potential consequences that the clinician must keep in mind when making the diagnosis of lumbar HNP. We used the theorem by Bayes, in conjunction with well-established results in the orthopedic literature, to calculate the probability of lumbar HNP given only a positive MRI finding. The necessary information provided by the orthopedic literature includes the prevalence of lumbar HNP, the probability of a positive MRI finding given that there is no HNP, and the probability of a positive MRI finding given that there is HNP. We found that the probability of lumbar HNP given only a positive MRI finding was 8%. The probability that there is no lumbar HNP, even when there is a positive MRI finding, is 92%. Clearly, MRI scans cannot be trusted as the sole source of diagnostic information.
Highlights
Herniated lumbar discs (HNP) are a large problem in the Western world
After substituting the numbers provided in the foregoing paragraph into the appropriate places in Equation (1), we find that the probability of lumbar HNP given a positive MRI finding is .0765, or under 8%
Given the low base rate for lumbar HNP (3%), the finding that the probability of lumbar HNP given a positive MRI result is less than 8% is not mathematically surprising to researchers who are familiar with Bayesian analyses
Summary
Herniated lumbar discs (HNP) are a large problem in the Western world. Andersson found that 1–3% of the population of Finland and Italy had HNP (Andersson, 1991). Researchers who have investigated other populations obtained similar findings (Borenstein, Wiesel, & Boden, 1995; Frymoyer, 1988; Lawrence et al, 2008). This condition is one of much pain and suffering for the afflicted patient, to say nothing of the financial cost. David Trafimow is a distinguished achievement professor of psychology at New Mexico State University, a fellow of the Association for Psychological Science, executive editor of the Journal of General Psychology, and for Basic and Applied Social Psychology He received his PhD in psychology from the University of Illinois at Urbana-Champaign in 1993. His current research interests include attribution, attitudes, crosscultural research, ethics, morality, methodology, and potential performance theory
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