with physical violence. A nine-nation study within the European Union found that current or ex-partners were the perpetrators of around 25% of all sexual assaults, and that violence was more common in assaults by ex-partners (50% of the time) and partners (40%) than in assaults by strangers or recent acquaintances (25%). Attributing the effects of marital rape in research is problematic as it is nearly impossible to find a large enough sample of spouses to study who have experienced sexual violence but have not also been physically assaulted by their spouse. Marital rape can spread sexually transmitted diseases and HIV, adversely affecting a victim's physical and psychological health. In sub-Saharan countries with very high prevalence rates of HIV, such as Lesotho, instances of multiple partnerships and marital rape exacerbate the spread of HIV. While rape by a stranger is highly traumatic, it is typically a one-time event and is clearly understood as rape. In the case of rape by a spouse or long term sexual partner, the history of the relationship affects the victim's reactions. There is research showing that marital rape can be more emotionally and physically damaging than rape by a stranger. Marital rape may occur as part of an abusive relationship. Trauma from the rape adds to the effect of other abusive acts or abusive and demeaning talk. Furthermore, marital rape is rarely a one-time event, but a repeated if not frequent occurrence. Whether it takes place once or is part of an established pattern of domestic violence, trauma from rape has serious long-term consequences for victims regardless of whether the assault is prosecuted or not. Unlike other forms of rape, where the victim can remove themselves from the company of the rapist and never interact with them again, in the case of marital rape the victim often has no choice but to continue living with their spouse: in many parts of the world divorce is very difficult to obtain and is also highly stigmatized. The researchers Finkelhor and Yllö remarked in their 1985 metropolitan Boston area study that: "When a woman is raped by a stranger, she has to live with a frightening memory. When she is raped by her husband, she has to live with the rapist". Relation to other forms of marital violence The historical (and present day in jurisdictions where it still applies) immunity of husbands to have sexual relations with their wives