Medical diagnosis and Prognosis are often wrong
Medical diagnosis and prognosis are based on probability, not certainty.
Despite doctors’ best intentions and the best technology, diagnosis and prognosis are often incorrect.
That means, if ‘assisted dying’ would be legalised, some people will die based on receiving incorrect information: They will request death based on the belief that they have a certain medical condition, when they don’t. They may believe that their condition is irremediable or terminal, when in fact it isn’t. Their decision about when they want to die may be based on an incorrect prognosis (estimation of how long they have to live.)
Diagnosis is often wrong
- “A wide variety of research studies suggest that breakdowns in the diagnostic process result in a staggering toll of harm and patient deaths. These include autopsy studies, case reviews, surveys of patient and physicians, voluntary reporting systems, using standardised patients, second reviews, diagnostic testing audits and closed claims reviews.” 
- “Arthur Elstein, a cognitive psychologist interested in ‘how doctors think’, studied clinical decision making for his entire career and concluded the diagnosis is wrong 10–15% of the time. A diverse range of research approaches that have focused on this issue over the past several decades suggest that this estimate is very much on target.”
- A 2012 study found that 28% of autopsies report at least one misdiagnosis.
- An autopsy-confirmed study found that false-positive diagnosis (people falsely diagnosed as having a particular condition) increased from 7% in 1989 to 15% in 1999/2000.
- “Many patients come to Mayo Clinic for a second opinion or diagnosis confirmation before treatment for a complex condition. In a new study, Mayo Clinic reports that as many as 88 percent of those patients go home with a new or refined diagnosis – changing their care plan and potentially their lives. Conversely, only 12 percent receive confirmation that the original diagnosis was complete and correct.” 
Prognosis is often wrong
Prognosis is a medical prediction of the course of a disease over time and the chance of recovery.
- A study of doctors’ prognoses for terminally ill patients found that only 20% of predictions were accurate (within 33% of actual survival time).
Some real-life examples of wrong prognosis
- In 2011 Lecretia Seales was “given only weeks to live…. Since then, the predicted weeks have stretched into three-and-a-half full and active years.” She died about six months after the cited article was published.
- Baroness Ilora Finlay of Llandaff, a palliative care specialist and politician from the UK, said:
“Let me tell you about one patient I had: In 1991 four of us, senior doctors, not just me, three others, all thought that his life expectancy was about three months. He was extremely distressed. He was desperate for euthanasia, but, because I couldn’t accede to his request, the law actually held my hand, stayed me. He seemed to be absolutely clear-cut in his request and fitted all the criteria of every bill I’ve ever seen, but he is still alive today. We managed his pain, we managed his disease. He had a little bit more treatment. His request vanished, and actually, sadly, 11 years later his wife died unexpectedly and he was left to bring up his children. And he’s brought them up and he says: “What would have happened to my kids if you’d been able to euthanase me? Don’t go there.”
“Personally, I’ve had my own experience as well in that my mother was really desperate to end her life when she was diagnosed with advanced breast cancer. She was actually quite angry with me for opposing the legislation at the time. And she was in a hospice at the time and thought to die within weeks, or even days. And the hospice medical director said to me: “How are you gonna cope when your Mum dies?” Actually, because she couldn’t have assisted suicide, and because she had the care that she needed, her pain became under control, she got going again and she lived for 4 years, independently, at home. We’d go out shopping and she said that they were the four richest years of her life but she never thought that she would have them. And we all value that.”
 Elstein, A. Clinical reasoning in medicine. In: Higgs, J., ed. Clinical reasoning in the health professions. Oxford, England: Butterworth-Heinemann Ltd, 1995;49–59.
 Berner, E., Graber, M. Overconfidence as a cause of diagnostic error in medicine. Am J Med 2008;121(5 Suppl):S2–23.
 Winters, B., Custer, J., Galvagno, S. M. Jr., Colantuoni, E., Kapoor, S.G., Lee, H. W. Diagnostic errors in the intensive care unit: a systematic review of autopsy studies. BMJ Qual Saf. 2012(21), 894-902. Retrieved from http://qualitysafety.bmj.com/content/21/11/894
 Zimmermann Young, E. (2017, April 4). Mayo Clinic researchers demonstrate value of second opinions. Mayo Clinic News Network. Retrieved from http://newsnetwork.mayoclinic.org/discussion/mayo-clinic-researchers-demonstrate-value-of-second-opinions/
 Van Such, M., Lohr, R., Beckman, T. and Naessens, J. M. Extent of diagnostic agreement among medical referrals. J Eval Clin Pract. 2017, Aug;23(4):870-874. doi: 10.1111/jep.12747. Epub 2017 Apr 4. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/28374457?dopt=Abstract
 Christakis, N. A., Smith, J. L., Parkes, C. M., and Lamont, E. B. Extent and determinants of error in doctors’ prognoses in terminally ill patients: prospective cohort study. BMJ 2000; 320:469. Retrieved from https://doi.org/10.1136/bmj.320.7233.469
 Macfie. R. (2015, January 8). Dying wishes. The Listener. Retrieved from http://www.noted.co.nz/health/health/dying-wishes/
 Radio New Zealand. (2015, June 5). Lecretia ‘was still able to smile’. Retrieved from http://www.radionz.co.nz/news/national/275447/lecretia-‘was-still-able-to-smile’
 Euthanasia-Free NZ. (2017, June 26). Transcript of Baroness Ilora Finlay of Llandaff’s interview with Mark Sainsbury on RadioLive. Retrieved from http://www.euthanasiadebate.org.nz/interview-with-baroness-ilora-finlay-with-mark-sainsbury-on-radiolive/