This is a difficult concept, and especially difficult to attempt to compare to modernity. Firstly, the concept of what constitutes a rape and even more so 'sexual violence' has changed dramatically. Secondly, we can only measure this according to court statistics. Thirdly, what time-scale or metric do we use?

To speak to this last point, a study co-authored by the Ministry of Justice (MoJ), Office for National Statistics (ONS) and Home Office released its first ever joint Official Statistics bulletin in January 2013. I will quote rather than attempting to synthesize this:

Prevalence of sexual offences

Based on data from the 2009/10, 2010/11, and 2011/12 CSEW, females were much more likely than males to have reported being a victim of a sexual offence; this was the case across all sexual offence categories. Overall 2.5 per cent of females and 0.4 per cent of males had reported experiencing some form of sexual offence in the last 12 months (Table 2.1). For both sexes, the vast majority of incidents are accounted for by “other sexual offences”, which include offences relating to indecent exposure, sexual threats and unwanted touching.

Focusing on the most serious sexual offences (including attempts), 0.5 per cent of female respondents had reported being a victim in the last year. Of these, the majority had been a victim of rape and two fifths a victim of assault by penetration. Males were much less likely than females to report being a victim of a most serious sexual offence (0.1 per cent). To put these figures into context, over the same period, 2.2 per cent of adults had been a victim of a violent crime resulting in injury in the last 12 months.

Based on these revalence rates, it is estimated that there were between 430,000 and 517,000 adult victims of sexual offences in the last year over these three survey periods (Table 2.2). Of these, it is estimated that there were between 366,000 and 442,000 female victims and between 54,000 and 90,000 male victims. With regard to the most serious sexual offences, the survey estimated the number of females who were victims ranged between 68,000 and 103,000 and male victims between 5,000 and 19,000 per year.

On the other hand, 19.6 per cent of females had been a victim of a sexual offence since the age of 16 and 2.7 per cent of males had been. [Report, 2013, p.18]

So which metric should we use for considering the medieval evidence? Per annum or throughout the course of life, since the age of 16?

Well we run into massive problems of both sources and demography. We aren't able to make incredibly accurate estimations of medieval populations.

This feeds into problem one (what constitutes sexual violence?). From the law codes we know that there was a punishment for rape. In Wales, to pick an obscure example, Cyfraith Hywel (Laws of Hywel) discussed rape in a largely economic manner. As the woman (and her kin) would now be responsible for a payment to her lord called the amobr.

In three ways amobr becomes due for a woman: by gift and transfer, although she not be slept with; and the second, by sleeping openly, although there be | neither gift nor transfer; and the third, by her pregnancy. [54-55]

Rape meant that the lord was deprived of his rightful fine, the king's law had been breached, and the woman and her kin had been done an injury or insult (sarhaed).

If it happens that a woman says of a man that he raped her and the man denies it, let him give the oath of fifty men without aliens and without designated men. If it happens that she makes a legal charge, let her take the man’s member in her left hand, with her right hand on the relic, and let her swear by the relic that the member had connexion with her by force and that blemish and sarhaed were done to her and to her kin and to the lord. Some of the justices do not allow denial against that: the law however says that it is right to allow denial as we have said above. [51]

If it happens that a man admits raping a woman, let him pay twelve kine as dirwy to the King, and her amobr to her lord, (and if she is a maiden, her cowyll), and her agweddi at the highest rate to which she is entitled, and her wynebwerth, and her dilysrwydd. | And if she is a married woman, her sarhaed augmented by a half. [51-52]

There is in the law of Hywel no castration of a man for raping a woman. Bleg. [52]

If two women are walking through any place and there is no one with them, and two men come upon them and copulate with them, no compensation is made to them; if, however, there is one person with them, however small (unless it is a carried child), they lose none of their right. Cyfn. [52]

If a woman travels alone, and a man comes to her and rapes her, if the man denies it let him give the oath of fifty men, three of them being under vows that they will not take a wife and will not eat meat and will not ride horses ever. If he does not want to deny, let him pay the woman her endowment and her dilystod, and a dirwy and a silver rod to the King in the manner which is right. If the man cannot pay, let his testicles be taken. If there were two women, let him give one testicle to one and the other to the other if he lies with them both. Cyfn. [52]

• (ed. and trans.) Dafydd Jenkins, The Laws of Hywel Dda, Dyfed, 1986.

So we need to find a way to weight our evidence to account for what constitutes sexual violence in a modern sense for which we cannot rely on the my second problem: the court records themselves.

We know Wales had laws focused on punishment for rape. Do you know how many court records we have? Two.

Two court records for any cases tried under Welsh law. Neither of these relate to rape. So what can we usefully say about Wales in the medieval period? How can we usefully compare this to the modern report which includes modern Wales?

I made this post not because the issue of rape is unimportant or not worth studying but because the manner in which you are approaching it is not useful or even viable. ASOIAF is a piece of modern literature based very loosely in a medieval setting. When George RR Martin says we can't ignore rape in warfare he is speaking about modernity rather than medieval history. No one is ignoring rape and ravishment in medieval warfare!

The issue is important but this is entirely the wrong manner of thinking about it usefully. If I could say, 'Oh! Well rape was more common in the Middle Ages, by x or y per cent.' What use is that to you? Do you feel better because we've stopped raping by a factor of z? What if the difference is negligible?