Scotland’s ‘not proven’ verdict does affect jurors decisions – but removing it may not improve rape conviction rates

Anyone who has served on a jury or watched a courtroom drama knows that most trials end with a verdict: guilty or not guilty. But in Scotland, there is a third option: not proven.

This acquittal verdict has the same legal implications as a not guilty verdict: the accused is able to walk away from the courtroom, innocent in the eyes of the law. However, as our research shows, it also significantly reduces the conviction rate in some trial types.

Now, the Scottish parliament has introduced the Victims, Witnesses and Justice Reform (Scotland) Bill.

The bill, which has passed its first Holyrood vote, would remove the verdict option as part of a series of reforms of Scotland’s legal system. Major political parties in Scotland have, for years, expressed support for either abolishing or reviewing the verdict, reflecting a growing consensus that it may be time for a change.

Those who oppose the not proven verdict and want to abolish it suggest that its existence may be contributing to Scotland’s dismal conviction rates in rape trials. They also say it can lead to misunderstandings among jurors, who are not provided with specific definitions or guidance on distinguishing between the not guilty and not proven verdicts.

Proponents of the existing system argue that it directs jurors to focus on the proof provided by the court, protects against injustice and mirrors realistic decision-making. One group that has been particularly vocal about removing the not proven verdict is sexual assault charities, such as Rape Crisis Scotland.

The not proven verdict is used disproportionately in rape and sexual assault trials, making up 44% of acquittal verdicts. Sexual assault survivors also suggest that the verdict feels like a “slap in the face”. They often say it causes them distress, as it suggests that the jury thought they were lying.

Likewise, the not proven verdict can cause the public to doubt the innocence of the accused, despite their being acquitted.

There are also concerns about whether the not proven verdict contributes to the acquittal of individuals who might have been convicted in other jurisdictions. In our research, we used evidence from several experiments to evaluate this claim.

The effect of the three-verdict system

As part of a team of experts from the University of Glasgow, Glasgow Caledonian University and the University of West of Scotland, we have conducted a comprehensive meta-analysis – the gold standard when considering empirical evidence – on the effect of the not proven verdict on juror decisions. To do this, we analysed data looking at how verdicts were reached in different types of mock trials, including sexual assault, physical assault and murder, in both the Scottish three-verdict system and the Anglo-American two-verdict system.

We examined the verdicts of 1,778 jurors in ten mock trials – all conducted by different researchers independently – through our meta-analysis. We found that jurors’ odds of conviction are approximately 40% lower under the three-verdict system (guilty, not guilty and not proven) when compared to the conventional two-verdict system (guilty and not guilty). In other words, the not proven verdict significantly reduces the likelihood of a conviction.

Of course, the studies were based on mock trials, not real-life scenarios, which may be influenced by different factors. For example, mock jurors know that their decisions do not have consequences. But in the largest studies we looked at, the trial reconstructions were approved by legal experts, and jurors were given real legal guidance on verdicts.

Our findings show that jurors may make different decisions depending on the choices available – and may be less likely to convict in the three-verdict system.

What would abolishing ‘not proven’ do?

Abolishing the not proven verdict would reduce confusion and ambiguity in the criminal justice process and make the Scottish system more consistent with the rest of the UK.

As our findings suggest, it may also increase overall conviction rates. Whether this increase is a positive or a negative is less clear, as mock trials and field studies can never test the accuracy of a juror’s or a jury’s decision. (In reality, nor can real trials, as it is impossible to know if a jury has reached the “correct” decision.)

Whether it might improve conviction rates in rape and sexual assault cases specifically is less clear. There were not enough trial types in our study to show whether the removal of the not proven verdict had a particular influence on specific trial types.

A paper published in 2019 found that the availability of not proven did not have a significant effect on conviction rates in the rape trial they studied (either at the juror or jury level). Other research has made comparable findings.

In rape and sexual assault cases, other factors are likely to affect the outcomes, such as jurors believing in rape myths – for example, that intoxicated people are partly to blame if they are assaulted.

Another factor may be the type of juror voting system used (for example, a simple majority versus a unanimous verdict). The 2019 study found that the simple majority rule leads to an increase in convictions in sexual assault trials, when compared to the unanimous rule.

Overall, the evidence suggests that abolishing the not proven verdict may not affect rape conviction rates as much as other crime types. But its removal may still be seen as positive by survivors of sexual assault, as many have said the three verdict system has caused them distress.

Lee John Curley receives funding from the Leverhulme Trust and the British Academy.

Elaine Jackson, Fiona Leverick, and Martin Lages do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.