Answering the question can seem to be a simple matter of adding up the costs and benefits resulting from the measures. But things are a lot more complicated than that. What counts as a benefit or a cost is far from obvious. Even if we agreed to what they were, finding a common measure to compare them is riddled with objections. Ultimately, no algorithm can tell us whether the policies were worth it, it’s all down to human judgement writes Stephen John.

According to some analysts, a year of lockdown measures cost the UK economy £251billion. Was it worth it? You might think that the 251billion figure is too high or too low. Maybe the true cost was "only" £25billion. Still, would that have been a price worth paying? These aren't just questions for future historians. Rather, as worries around vaccine effectiveness against new variants grow and previously untouched countries go into lockdown, policy-makers around the world need to decide: when is the cure worse than the disease?

There's a way of thinking about the question, central to health economics, thrown around in debates around the pandemic: that we should adopt lockdown policies only when their benefits outweigh their costs. This answer is simple and appealing. Unfortunately, it's also false. Or, at least, it's an answer which hides far more than it illuminates. While it may be tempting to think that there must be some number - lying, say, between 25.1million and 251trillion - at which the costs of lockdown outweigh the benefits, this is an illusion.

To see why, it's useful to take a step back to think about the appeal of the notion that we should choose policy according to the net balance of costs and benefits.

Imagine a highly stylised example, associated with the philosopher John Taurek: you are a lifeboat captain; on one island, one stranger is about to die; on a second, nearby island, five strangers are about to die; you can save the one or the five, but unfortunately, not both. What should you do?

Even if we only focus on the health-related consequences of lockdown, most health economists think we should also consider "quality of life".

Faced with this horrible dilemma, most people think you should save the five. There is an obvious way of spelling out this intuition: in general, all else being equal, we should do as much good as possible. Plausibly, a situation where five lives are saved is better than one where one life is saved. Therefore, we should save the five, rather than the one. Of course, this is horrible for the one, but, still, the alternative would be worse.

This kind of stylised example is a long way from decision-making about Covid-19 and lockdowns. Still, it is easy to see how the same basic logic can be used to defend lockdown measures: had we done nothing, many more lives would have been lost. Therefore, lockdown measures were like the captain's choice: tragic, but necessary.

However, once we have made this move, matters quickly get murky. Imagine that the lifeboat captain gains some more information and learns that the one stranger is 80 and can expect to live ten more years if saved; each of the five strangers is 89 and can only expect to live one more year. Now, we might reason as follows: saving the one gains ten "life years", whereas saving the five only gains five "life years". So, saving the one would generate greater benefit.