MPs Vote on Assisted Dying for the Terminally Ill

The bill before the House today turns on a single figure: six months. Members are voting on whether terminally ill adults in England and Wales may seek assisted dying once two doctors certify a prognosis of six months or less to live. The official account treats this figure as a clean threshold - as though a doctor’s estimate of remaining life were a thermometer reading, precise enough to bear the weight of an irreversible act. The data says otherwise: prognosis of survival time is reliable in the aggregate and unreliable in the particular case, and it is the particular case that Parliament is legislating for.

Consider what “six months” actually is. It is not a measurement taken from the patient; it is a probability drawn from a cohort of patients who resembled this one in diagnosis, age, and stage of disease. When a physician tells a family that six months remain, she is reporting the median of a distribution, not a fact about the person in the bed. Some in that distribution die within weeks. Some live for years. The average is sound; the individual application of it is a wager dressed as a certainty. I have watched soldiers given days to live walk out of Scutari’s wards a year later, and I have watched men pronounced fit for transport die before the ship sailed. The instrument that failed the War Office by aggregating deaths into misleading averages is the same instrument now being asked to certify individual deaths with precision it was never built to provide.

The bill’s safeguard is the requirement of two doctors’ agreement. This sounds, to a legislator unfamiliar with the mathematics of measurement error, like a doubling of certainty. It is not. If both doctors are drawing their estimate from the same population data, the same clinical heuristics, the same systematic tendency to underestimate survival in cancer and overestimate it in organ failure, then a second signature does not correct the bias - it repeats it. Two clocks set to the same wrong time do not, between them, tell you the hour. What would reduce the error is not a second doctor but a different method of estimation altogether, and no such method is written into the bill going through the House today.

I do not say this to defeat the compassion behind the bill. The stakes named for this debate are real: adults facing the last months of terminal illness are asking Parliament for the choice to end suffering on their own terms, and I have nursed enough of the dying to have no patience for those who wave away that request with talk of sanctity untested by a single night on a ward. My objection is narrower and, I think, more dangerous to ignore. A law that certifies eligibility on a prognosis known to carry wide individual variance will inevitably authorise the deaths of some patients who, left alone, would have lived considerably longer than six months - and will just as inevitably deny relief, in the delay of certification, to some who die before the paperwork is signed. Both errors are invisible in the debate today because the six-month figure is being treated as a fact rather than an estimate with a margin the bill does not acknowledge.

What follows from this is not that Parliament should reject the principle, but that it has built its central safeguard on the wrong statistic. The number that matters is not six months; it is the width of the error around six months, broken down by diagnosis, and no such table has been laid before the House. Until it is, MPs voting today are certifying a threshold whose precision they have assumed rather than measured - and a patient signing the final form, surrounded by family who trust the number on her chart, deserves to know that the six months written there is a guess dressed in the authority of medicine, not the diagnosis itself.