Tackling population health challenges as we build back from the pandemic

Dear Editor

A Natural Experiment on the Northern Line

I regularly use the Northern Line for getting around London, I try to avoid the rush hour but after 10.00 the journey is quiet, a time for contemplation and critical thinking.

Yesterday morning I experienced a Damascene moment.

I board the train at Golders Green where the train runs overground, bound for Belsize Park near the HQ of the University of the Third Age (U3A), where I deliver a course of lectures to the elderly on the subject of medical humanities. I was running a little late, so I jogged up the steps to the platform whilst putting on my mask. I was wearing a baker’s boy cap, glasses, and hearing aids, so my ear lobes were rather over-loaded. It was a chilly morning, so my glasses steamed up on boarding the tube. I nearly lost a hearing aid worth £1,500 and nearly trapped my foot in “the gap” between the platform and the carriage. I collapsed inside the carriage with a complete loss of my professorial dignity and a twisted ankle. All this is one of the unintended consequences of wearing a face mask.

I settled down and scanned the carriage to see if anyone had noticed, but my fellow passengers were head down looking at the smartphones. Three other observations suddenly triggered a strategy for a natural experiment regarding the value of social behaviour in slowing the spread of the next variant of COVID-19.

First, I confirmed that social distancing was maintained as always after the morning rush hour, next I confirmed that the demographics of my fellow travellers were as always, but unlike previous weeks, 100% were wearing masks compared with 50% that I’ve come to accept as normal. The demographics that seem to define non-wearers of masks, were predominately defined by age, sex and clothing. The worst offenders are heavily tattooed young men wearing jeans with fashionable ragged holes around the knee. The most compliant were post-menopausal women wearing normal winter garb with only one piercing of the ear lobe. The design of my natural experiment sprang to mind as written in a diagram in the protocol of the study. The population of the study would be a large random group of citizens served by the Northern Line. The outcome measures would be incidence of viral illness, hospitalisation, cause-specific mortality, and all-cause mortality that include unintended consequences as illustrated by my near-miss. A 2x2 factorial design with four cells, will allow us to examine the benefits of masks, social distancing or a combination. Rush hour v non-rush hour will be a good surrogate for social distancing, demography, as described, would be a good surrogate for mask-wearing, rush-hour + demography will be a good surrogate for the combination. The fourth empty cell acting as a control would be those who don’t travel by tube. The final comparison would be the month before masks were made mandatory versus the month after they were made mandatory. So, in the end, the study ends up as 2x2x2. If anyone can’t follow that design, then clearly, they have no idea about Evidence-Based Medicine.