A/B test

In an earlier post I showed how a comparison of two different, though similar, provinces of Italy which had adopted different approaches to containing the Coronavirus outbreak could serve as a kind of statistical trial on the relative effectiveness of the strategies. A similar argument has now been made in respect of Ireland and the UK by Elaine Doyle. This is the first tweet in her thread, showing that Ireland and the UK started off with similar resources to fight the pandemic:

But, at the time of writing, the UK had far more fatalities than Ireland. Elaine writes:

As of today, there have been 320 deaths from the coronavirus in Ireland, and 9,875 deaths in the UK.


As of Saturday 11 April, there have been 6.5 deaths per 100,000 people in Ireland. There have been 14.81 deaths per 100,000 people in the UK. Guys, people have been dying at more than *twice the rate* in the UK

Elaine argues that since the countries are comparable in most respects, it’s reasonable to assume that the difference in outcomes is attributable to the difference in approaches.

The complete thread of her argument is available here. She writes:

You have a real-time A/B test happening *right in front of you

In other words, you can think of Ireland and the UK as two equivalent units. To one unit (Ireland) you’ve applied ‘treatment A’, a fast and decisive lockdown. To the other (UK) you’ve applied a slower, more gradual, lockdown. And the difference in outcomes is due to the difference in treatments.

This argument isn’t universally agreed on. Other experts argue that there are other fundamental differences between Ireland and the UK – for example, Ireland has a much greater proportion of its population living in rural areas – and these are just as likely to impact on the numbers of COVID-19 cases as the differences in the strategies applied. This is no doubt true. And a true A/B test  would have comprised random allocation of treatments to more than two countries. The lack of randomness in the allocation is a serious hinderance to interpretation, though a comparison of just 2 countries is dangerous in any case.

In time, it might be possible to compare many different countries according to the strategies adopted, accounting for different geographical and demographic factors, and decide which strategies are most effective. This type of analysis was discussed in an earlier post for the 1918-19 influenza epidemic, though I’m guessing we won’t want to wait 100 years to carry out such an analysis for the current pandemic.

Update: since writing this post, Elaine Doyle has written an article for the Guardian setting out her arguments.

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