The Amicable Society's own 1811 mortality experience was the first data on assured lives available to actuaries, and it was more favourable than the Northampton table

Around 1811 the Amicable Society's registrar, a Mr. Pensam, compiled the Society's own mortality experience from its records. Walford records both what it showed and why it mattered: it "was found more favourable than that shown by the Northampton Table. This was the first actual Mortality Experience of Assured Lives which had been available to Actuaries, and so was regarded with great interest." A fuller analysis of the same records was produced in 1841 by a later registrar, Thomas Galloway — who turns out, per observation-galloway-is-a-third-astronomer-actuary-instance, to have been a Royal-Medal astronomer at the same time.

The significance is in the phrase "of Assured Lives." Every mortality table the field had until then — Halley's 1693 Breslau table from parish registers, and Price's Northampton table that became the standard for roughly a century — described a general population. Pensam's compilation described the specific population that actually buys life assurance, which is not the same population and had never been separately measured.

That it came out more favourable than Northampton is the expected direction, and it bears directly on the Northampton table's known bias — though the two effects are distinct and shouldn't be collapsed. Northampton overestimated mortality as a property of the table itself, a bias that favoured insurers selling assurance. An assured-lives population would also be expected to die more slowly than the general population for a separate reason: the people who buy life assurance are screened, in the Amicable's case by an age band at the door and a committee "cross-examination as to health, habits, &c." Walford states the finding without explaining it; the selection reading is inference, not his.

There is a quiet irony in where this data came from. The Society that produced the field's first assured-lives mortality experience was the one that had spent the previous century refusing to price by age and had only just adopted a graded scale in 1807. Its records were valuable to actuaries precisely because it had been running a large, long-lived, age-screened pool — the institutional accident of insuring the same kind of person for a hundred years turned out to be a dataset.