Disease definitions and treatment thresholds are often based on dichotomisation of continuous variables. Examples of these dilemmas are the definition of hypertension and the continuum of pathologies in polyps in colorectal cancer (CRC) screening. Continuous variables are a clinical dilemma since they make it difficult to determine when to diagnose and intervene. Dichotomisation requires per definition a threshold which results in an epidemiological dilemma: if the threshold is set too low, too many people are overdiagnosed and overtreated, whereas if the threshold is set too high, too many people are underdiagnosed and undertreated.
We will present empirical research on these dilemmas and then have a discussion on how to solve them. We will present research on the following dilemmas:
Increasing blood pressure levels are related to an increasing absolute risk of cardiovascular disease and mortality, and it is an oversimplification to determine who has hypertension based on a fixed threshold.
The threshold for an abnormal screening result partly determines the balance between benefits and harms in cancer screening. We will explore the implications fixed thresholds have for people using examples from CRC screening.
In CRC screening the detection and the definition of polyps as cancer precursors pose two dilemmas. These result in an increasing number of people being diagnostically labelled as a consequence of the spectrum of normality becoming narrower.
CRC screening consists of two parts: a faecal occult blood test and the following investigative colonoscopy. People who decline the colonoscopy after a positive faecal test find themselves in doubt, feeling healthy but with a positive result of screening.
With the increased use of PSA–blood tests the detection of low–grade prostate cancers has increased. Most of these low–grade cancers are indolent and will never cause harm by themselves, whereas there is a great diagnostic uncertainty when it comes to finding those few that will.
Citizen juries as a method for improving lay people’s understanding and eliciting their preferences in relation to harms and benefits of cancer screening. Cancer as a dichotomised variable as one of the most serious causes of harm.
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