• Heather D. Flowe, PhD

Tonic immobility: Why it shouldn't be a part of rape law reform

Updated: Nov 6


Tonic immobility – the idea that someone enters a state of involuntary paralysis when being sexually assaulted – is a popular concept in discussions about rape law reform.

While reforming rape law is crucial in improving prosecution rates, the introduction of tonic immobility as a reason for doing so is deeply problematic– not least its implication that victims would and should have fought back were they not ‘frozen’ in fear.

Sweden makes for an interesting case study on the use of tonic immobility to argue for rape law reform.

The country changed the legal definition of rape in 2018 to ‘sex without consent’. As a result, prosecutors do not have to prove the use, or threat, of violence or coercion. Rape conviction rates have risen 75% in the two years since, prompting calls for other countries to follow suit and revamp their legislation.

The increase in rape convictions is undeniably good news. However, a deeper look at the reasons given for the change in law are troubling. Namely, that sexual assault victims reportedly freeze during the attack and can’t fight back.

Per the Reuters article above, “Police and courts often query a victim’s story if she did not retaliate, but there is growing evidence that many victims experience temporary paralysis when raped.”

This, some argue, is why many victims do not fight back. Helping victims to understand that paralysis is a normal biological reaction to an overwhelming threat will help victims manage the feelings of guilt or shame they may feel for not having resisted, goes the argument.

Now, it is worth pointing out that this line of argument is well-intentioned. Those who have lobbied for this change in law and people like myself are very much on the same side, looking to increase prosecution rates and support victims of sexual assault and rape.

However, there is a deeply problematic thread to it.

The line of argument implies that if victims could fight back, then we would expect them to.

But, for what other crime do we expect the person being attacked to fight back?

We don’t ask a victim of robbery if they fought the assailant to determine whether their wallet was stolen. We also don’t tell them not to blame themselves because it was an expected biological reaction to not have fought back.

The application of tonic immobility to courts and the law is victim blaming in disguise. It says to victims who did not experience tonic immobility that they should have fought back. And what if a victim says that she did not fight back and yet was not frozen in fear? Do we want a policy precedent that suggests that the perpetrator should not be prosecuted or convicted in these circumstances?

Justin Dillon, a Washington, D.C., attorney who defends students across the country accused of Title IX violations, told me that a couple of years ago he had barely heard of this condition, but that its terminology has swiftly made its way into campus adjudications: “I don’t think I’ve seen a complaint in the past year that didn’t use the word frozen somewhere.” -The Atlantic, The bad science behind campus response to sexual assault

There are also numerous fundamental conceptual and statistical issues that arise in measuring tonic immobility that I think are important to point out.

First, the concept of tonic immobility comes out of the literature on other animals, including sharks and rats. There have been no objective studies in humans to establish whether the concept and theory can be generalised to humans. There already have been round criticisms in this regard.

Tonic Immobility in sharks. See it here.

Second, attempts to statistically validate subjective measures of tonic immobility raise serious questions about its measurement validity.

To illustrate these problems, take the paper by Möller, Söndergaard and Helström (2017) referenced in the Reuters article. It reported that 70% of rape victims had experienced “a state of involuntary, temporary motor inhibition known as tonic immobility”. This would appear to be part of the evidence-base used to support the law-change.

In this study, tonic immobility at the time of the assault in 298 women was measured with the Tonic Immobility Scale. The scale supposedly measures tonic immobility (items 1-7 below) and fear (items 8-10 below) on a seven point Likert-type scale, where people can give an answer from 0-6.

The average rating (i.e., the mean) people gave for each item is given below (the standard deviation is in parentheses).

Data from Möller, Söndergaard and Helström (2017) :

(1) Froze or felt paralyzed during your most recent experience. 3.99 (2.12)

(2) Were unable to move even though not restrained. 3.67 (2.17)

(3) Body was trembling/shaking during the event. 3.17 (2.19)

(4) Were unable to call out or scream during the event. 3.70 (2.25)

(5) Felt numb or no pain during the event. 3.48 (2.23)

(6) Felt cold during the event. 3.11 (2.35)

(7) Felt feelings of fear/panic during the event. 4.57 (2.02)

(8) Feared for your life or felt as though you were going to die. 3.06 (2.36)

(9) Felt detached from yourself during the event. 4.37 (1.98)

(10) Felt detached from what was going on around you

during the event. 4.14 (2.00)

The data were not normally distributed, so interpret the means with caution, as they do not characterise the distributions very well. A total score across items greater than 21 is argued to represent ‘significant tonic immobility’, and a total score greater than or equal to 28 to be ‘extreme tonic immobility’.

A total of 70% of the sample were considered to have significant tonic immobility, and this is the statistic that was reported in the media.

But, there are significant problems here:

· The first big problem with this study (and all others like it) is that there is no control group. One recent study compared people who had never experienced a traumatic event (i.e., a control group) with people who have experienced a traumatic event. They found that the effect size for trauma exposure in how people answered the tonic immobility questions is small. In fact, only 4% of the variability in how people answer the questions is explained by having experienced a traumatic event, which is astounding.

This alone should make us very sceptical of the 70% figure.

· The concepts “significant” and “severe” are conceptually flawed. If a person answered below the scale midpoint (i.e., said 2) to every single item, they’d be classified as significant, and if they answered 3 –which is the middle of the scale (which is like saying somewhat, or sort of yes and sort of no), they’d be considered “severe”. This seems conceptually problematic to me.

· The questionnaire does not seem to capture immobility and fear. Rather, there seems to be one underlying factor that accounts for how people answer the questionnaire. (What is it? I don’t know. It’s some combination of fear, freezing, and being cold, unable to speak, feeling numb, perhaps feeling as though your life is threatened). Further, some items on the questionnaire have been shown to be redundant and unreliable.

· If data are not normally distributed (as is reported in the article to which the news article refers) the mean (average score) for a given item is not informative, particularly if the article does not report how the data are skewed.

· Finally, it is not clear when it comes to freezing whether people are describing how they behaved during the rape or how they felt during the rape, or how they feel they were when reflecting on the event now. Indeed, the items feeling and acting (items 1 and 2 above) have been shown to be completely redundant statistically.

Reforming rape law and policy is crucial in improving prosecution rates, but the introduction of tonic immobility as a reason for doing so is deeply problematic for the reasons outlined above – not least it’s implication that victims would and should fight back were they not ‘frozen’.

We want change to be sustainable, and that means using robust evidence (of which there is plenty, on memory, trauma, intoxication, crime-linkage and more), and not cherry-picking flawed papers which may, in time, be challenged in the courtroom.

© 2020 by  Heather D. Flowe, PhD