Juries of seven are now the way forward

Smaller juries don’t make worse decisions. Indeed, as we’ll see, there’s even some reason to think their verdicts might be fairer. Other arguments against sitting with smaller juries during this crisis are either misconceived or point to pocket fluff problems when compared with the imminent obliteration of our system of criminal justice.

There is now a backlog of no fewer than forty thousand Crown Court cases. Even pre-virus, waiting times had grown into a grim new normal where proposed trial dates contained years you’d never heard said out loud before. All jury trials stopped when the lockdown began, and the handful of “socially distanced” experiments that started a fortnight ago, taking up three courtrooms each and buckets of extra time, are not going to solve the problem. Nor will hiring a few empty leisure centres and lecture halls. We need trials to fit into one courtroom, and seven-person juries can help us achieve that.

There is of course an argument that we should do without social distancing in order to allow trials to proceed in the usual way. The twelve jurors could be selected by consent – as could the barristers, judges and defendants. I suspect there would be no shortage. Yes, the small increase in risk of transmission of the virus would slightly jeopardise the health of others not present but …I’m sorry, I can’t help it, I’m a Sumptionista on this. I’ll leave it alone, and proceed on the basis that substantial social distancing is going to be required for some considerable time to come.

Why twelve jurors? 

In 725 AD the Prince of Wales, Morgan of Glamorgan, is supposed to have said, “For as Christ and his twelve apostles were finally to judge the world, so human tribunals should be composed of twelve wise men”[1]. Or perhaps the US Supreme Court had it right in 1970 when they told us that the traditional jury size arose in the 14thCentury as a “historical accident”[2]. Either way it seems there was no double-blind RCT, or even a meta-analysis of observational studies, before it was rolled-out nationally.

But that doesn’t mean that twelve isn’t the best number of course. Far from it. Across human societies, ways of doing important things often improve over time – just as with biological evolution – by accidental variation and imitation/replication of successful strategies. Nice examples, given by polymath Philip Henrich in his recent book “The Secret of Our Success” (reviewed and explained brilliantly here) include the preparation of food and Inuit hunting methods: it seems likely that no individual, or even any group, worked out the incredibly complex and long-winded processes by which nardoo can be prepared for consumption, or by which seals can reliably be captured from beneath the ice. Instead, these fine-grained techniques were developed incrementally over long periods, by individuals and groups copying their more successful rivals’ partly random innovations. It’s possible that over the last thousand or so years, something similar has happened with jury size. 

But I doubt it. Twelve probably just felt like a sensible number, and it stuck.

Do bigger groups make better decisions?

It would be surprising if a “wisdom of crowds” rule applied universally.  The phenomenon of a large group of decision-makers breaking into a small number of opposing factions (often two, of roughly equal size) each with their own set of immovable but sub-brilliant beliefs and attitudes has become painfully familiar. To avoid this sort of problem big groups tend to delegate important decisions to small committees. But how small should they be? 

Well, Professor Simon Garrod of Glasgow University performed various experiments to try to answer this point and concluded as follows:

“The results…suggest that the size of a decision-making group influences what the group can achieve. If it is important to take into account the range of opinions among group members, then small groups should perform better. However, if the goal is to disseminate a particular opinion through a dominant group member (e.g. the leader of a team) then large groups should be more effective.” [2]

From “Group Discussion as Interactive Dialogue or as Serial Monologue: The Influence of Group”, 2001, available here

For taking into account a range of opinions: six or seven is the magic number, he said (see BBC report here).

Now, this is only one experiment and although it hasn’t been refuted as far as I’ve been able to discover, experts of Professor Garrod’s standing could probably be found to contradict him. But I think what we can say is this: it doesn’t look like the evidence points firmly towards a need for twelve-person juries in all circumstances.

It also occurs to me – though this is really just an intuition that an experiment might be able to test – that the larger the jury, the less the weight of personal responsibility each juror feels. And if I want my innocent clients to be acquitted (by far the most important outcome for any justice system) I want each juror to feel as much personal responsibility as possible.

Smaller juries used elsewhere

In the Cayman Islands, where I once spent a sunny year working as a defence attorney, most juries have only seven members. There was never any sense that the verdicts would have been better or fairer, had they emanated from full-English sized juries. And as is now well-known, during the second World War we ourselves reduced twelve to seven. 

It’s true that in both the Cayman and WW2 examples twelve-person juries were retained for murder and treason, which might indicate an acknowledgment of the superiority of the larger number. But it could just as easily have been an acknowledgement of the importance of perceptions, or of a lack of certainty: i.e. perhaps there is some non-trivial difference between twelve and seven, and it won’t cost much to keep those few who are accused of the most serious crimes from complaining. 

Scotland has juries of fifteen, with convictions by simple majority. Do they look upon our twelve-strong super-majority system with horror? Well, actually they might: in 2009 the Scottish authorities reviewed the position and, deciding to make no changes, concluded that they had “got it uniquely right”. Ha. (News article here)

And let’s not forget: we’ve been convicting people – including of murder – with juries of only nine for at least 45 years (see s.16 Juries Act 1974). That’s a serious problem for anyone arguing for the supremacy of the apostolic twelve.


One concern with the proposal to reduce the size of juries – of more relevance today than when it was last made in 1939 – is the fear that diversity (of opinion, experience, ethnicity, and so on) might be diminished. This is a valid concern: obviously, the probability of getting at least one individual with a given minority trait decreases as the size of the jury decreases. 

An example. 40% of London residents are BAME. The probability of getting at least one BAME juror is 99.8% (i.e. 1 – (0.6^12)). So, only 1 in 500 juries in London will be all-white. (This sounds like a rare occurrence, and it is, but there will be a roomful of people each year who were tried by an all-white jury in London – and of course in many parts of the UK an all-white jury is the norm).

But with only seven jurors the chances of at least one BAME member (in London) drops to 97.2%. It’s a drop, but it’s not a big drop. It’s not an order of magnitude. The point is that whatever problems are associated with variance in jury composition when we use juries of seven, are problems we’ve long had to contend with while using juries of twelve. 

And the increase in variance that’s an inevitable consequence of a smaller sample can also work in the other direction: with a twelve-person jury the chance of a BAME majority is 15.8% in London, but with a jury of seven it’s nearly double, at 29%[3].

Professor Cheryl Thomas QC’s groundbreaking research into juries in 2010, “Are Juries Fair?”, remains very much worth reading (see here for an annoying auto-download pdf link, which is all I could find). I won’t attempt to summarise her work in this post, but the section on diversity issues, between pages 14 and 26, suggests to me that the slight increase in variance that’s inherent in using juries of seven rather than of twelve is not going to lead to injustice on that score. 

Chesterton’s fence and tradition

G.K. Chesterton illustrated the risks of iconoclasm in 1929 by imagining a fence across a road, blocking your way. You might want to take it down, but you shouldn’t, he suggested, unless you know why it was put up. This principle could sensibly be applied to the details of how we run criminal trials.

Indeed, one of the many curious features of our jury system is that it has somehow come to occupy that tiny cultural niche where, at the slightest threat, it will be vigorously defended by all and sundry from across the political spectrum – particularly criminal lawyers, but also by the public. Even people for whom “outdated” is a term of deadly abuse will defend the jury system as it currently stands with all the reactionary fervour and appeal to tradition of an elderly Viennese aristocrat making a pitch for membership of the MCC rules committee. We don’t really know why it works, but we think it does, we’ve done it for a long time, many of the alternatives are truly awful, so let’s not muck about with it

But reducing twelve to seven in a time of crisis needn’t be seen as mucking about with anything. Instead let’s see it as a feature of our marvellous system. It worked during the war, it can work again.

To allay any remaining fears, we could also consider the following temporary measures: 

  • Do away with majority verdicts, at least for convictions. This is a subject for another post,  but they are of little benefit. They were only introduced in this country in 1967 in response to a national panic about organised criminals nobbling juries, and in America – where they were introduced in an explicit attempt to disempower black jurors – they have been outlawed by the Supreme Court, just a couple of months ago (Ramos v Louisiana 2020).
  • Make jury service voluntary.
  • Allow any defendant to wait for a twelve-person jury if he or she wants. 
  • A watertight sunset clause so that we return to using twelve the moment government guidance abandons social distancing. 

Even if – even if – there were some negative effect on justice caused by reducing the size of the jury, it would surely be very small. And it would be a choice between that very small potential injustice and the very enormous real injustice that is currently being caused by massive continued delays to trials. Long-delayed trials mean not only that guilty people go free, which we can sort of live with, but also, as memories fade and cross-examination ends up cutting less effectively to the truth, that more innocent people go to prison, which we really can’t.

[1]According to 19th Century jurist William Forsyth in “History of Trial by Jury”, here.

[2]Williams and Florida 399 U.S. 78

[3]The very large increase is largely down to seven being an odd number and twelve being even; but even with an eight-person jury, the probability increases noticeably – to 17.4%. If you want to check my arithmetic, for a seven person jury I calculated it as (0.4^4 * 0.6^3 * 7C4) + (0.4^5 * 0.6^2 * 7C5) + etc.

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