Since 1999, the National Institute for Health and Care Excellence has weighed costs against benefits to help the NHS decide what it should buy. The institute’s boss, Sam Roberts, calls it a mindful “health-care innovation shopper”. Within a fixed budget, every new drug it buys risks squeezing essentials like GPs or ambulances among existing health-care services.

We performed a longitudinal, retrospective cohort study involving adults 50 to 85 years of age who were included in the Health and Retirement Study and the Survey of Health, Ageing, and Retirement in Europe between 2010 and 2022. Wealth quartiles were defined according to age group and country, with quartile 1 comprising the poorest participants and quartile 4 the wealthiest. Mortality and Kaplan–Meier curves were estimated for each wealth quartile across the United States and 16 countries in northern and western, southern, and eastern Europe. We used Cox proportional-hazards models that included adjustment for baseline covariates (age group, sex, marital status [ever or never married], educational level [any or no college education], residence [rural or nonrural], current smoking status [smoking or nonsmoking], and absence or presence of a previously diagnosed long-term condition) to quantify the association between wealth quartile and all-cause mortality from 2010 through 2022 (the primary outcome).

The volume-outcome relationship has been a commonly invoked policy initiative aimed at improving the quality of healthcare. This inverse relationship between the caseload volume of patients treated and patient mortality has been described across many health settings and in many countries. Despite the large body of literature demonstrating this favourable relationship, most studies have focused on differentiating the effects of selective referral and the true effects of volume. In comparison, there are few studies evaluating the underlying mechanism of the volume-outcome relationship, namely dynamic learning-by-doing or the static effect of economics of scale. Resolving this tension between policies that allow providers to accrue experience over time and policies that promote centralisation of services would make a more compelling argument for policies such as minimum volume standards to be firmly established.