Intended for healthcare professionals

Analysis Essay

Overdiagnosis, ethics, and trolley problems: why factors other than outcomes matter—an essay by Stacy Carter

BMJ 2017; 358 doi: (Published 16 August 2017) Cite this as: BMJ 2017;358:j3872
  1. Stacy M Carter, associate professor
  1. Sydney Health Ethics, K25 Medical Foundation Building, The University of Sydney, NSW 2006, Australia
  1. stacy.carter{at}

If the only ethically important consideration was the balance of benefit to harm, overdiagnosis might be less contested, writes Stacy Carter. But evidence and intuitions from famous thought experiments could explain some peoples’ willingness to accept the harms of overdiagnosis—other factors may feel more important to them


Stacy Carter is associate professor at Sydney Health Ethics, a centre for theoretical and empirical ethics research at the University of Sydney. She specialises in the ethics of public health and conducts empirical studies to understand peoples’ values and reasoning about public health interventions. She tweets sporadically @stacymcarter.

In February 2014, the non-governmental Swiss Medical Board recommended that mammography programmes in Switzerland may eventually be closed down because they might not deliver more benefits than harms. In the resulting uproar the board was accused of being “unethical.”1

Controversy about mammography has persisted in the UK,2 US,3 Canada, and elsewhere,4 and disputes about overdiagnosis exist in prostate cancer,5 chronic kidney disease,6 attention-deficit/hyperactivity disorder (ADHD),7 and many other conditions. People concerned about overdiagnosis are compelled by evidence of harms outweighing benefits. But not everyone is equally compelled. This may be because of disagreements over the evidence,8 conflicts of interest,9 10 or cognitive biases.11 Another possible cause of disagreement is that some people may not think that benefits and harms are the most important consideration.

This contrast, between people who think outcomes are what matters most and people who disagree, is central to the discipline of ethics. It is a crucial difference between utilitarian ethicists and non-consequentialist ethicists. Broadly, utilitarians think that, given several options, we should choose the one that produces the best overall outcome (the most utility among the whole group of affected people), ensuring that each person counts equally in the calculation. …

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