How common is incest in the West?

about a third of people have a sexual experience with a relative

Sibling incest

As of date, there have been two large surveys of American undergraduates in New England on the rate of sibling incest: one found a self-reported rate of sibling incest (including playing doctor, petting, and intercourse) to be 12.5% (n = 796) and 17% (n = 526). There are many reasons to consider this an underestimate:

1. Social desirability bias: people are likely to under-report these relationships due to their taboo nature. In the first study, women were more likely to report having incestuous relationships (15%) than men (10%), even though most incestuous relationships are heterosexual. This was not due to women reporting more homosexual relationships; 62% of the reported homosexual relationships were male, while 38% were female.

2. Age: some sibling incest surely takes place after university years.

3. Socioeconomic status: these are samples of university students. Stereotypically, incest occurs most often in poorer, rural or dysfunctional households. I’m not sure if sibling incest would be more common in poorer households, but I would guess that it occurs more in rural families with unsupervised children.

4. Memory: some people may not remember sexual acts that happened when they were too young to register certain experiences as sexual. Given that incestuous relationships were reported at very young ages, I don’t think this is much of an issue.

Assuming that 5% of the incidents are forgotten, 1% happen after university years, the rate is 5% higher in the general American population, and that a quarter of remembered incest relationships are not reported, the true rate of sibling incest is likely closer to 22% instead of the reported rate of 15%.

For now, I would estimate the rate to be at minimum 15% and at most 25%.

Some people may consider this to be unreasonably high, but this is partially due to how expansive the definition is, the rate would lower from 22% to about 15% if playing doctor did not count as incest. Intercourse is rare.

from here

Cousin incest

One of the sources that I cited prior also tallied the prevalence of cousin incest, which found that 16% of the 266 boys and 17% of the 530 girls claimed to have had a sexual experience with a cousin. Assuming 5% of incidents are forgotten, 1% happen after university years, that the rate is 5% higher in the American population, and that a sixth go unreported (cousin incest is less taboo, so I assume it is not as underreported), the true rate is likely closer to 22%.

There is one sample of 831 sexually abused children in hospitals finds that cousin abuse was more common than sibling abuse, though I suspect that this is driven by selection: those abused by cousins are more likely to admit to it than those abused by siblings.

For now, I would estimate a minimum prevalence of 10% and maximum prevalence of 25%.

Parent ~ child incest

Studies disagree quite a bit on the prelavence of father-daughter incest:

• One survey of 3,769 15 year old girls in Finland found a rate of .5% and only one case of stepmother-son incest in the 3,666 Finnish boys.

• A study estimates the prevalence of father-daughter incest to be 1 in 20 in American and English families, 10 times larger than the one found in the Finnish study. Unfortunately, I do not have access to that paper, so I cannot evaluate why this discrepancy exists.

• This study, citing Kinsey and Finkelhor, claims that the rate is one in one hundred. I found Finkelhor’s book, and 5 of the 530 girls in the sample reported being abused by their fathers and none of the 266 boys reported having sex with their mothers; I could not find where in Kinsey’s book on the sexual behaviour of women did they find that 1 out of 100 women are sexually abused by their fathers.

From what can be observed, it seems that between 0.5% and 5% of Western women have sex with their fathers at some point in their lives, and about one in 1000 to 10000 men have sex with their father or mother at some point.

Avunclar incest

The Finkelhor study also asked individuals about incestuous relationships with aunts and uncles. 16 out of the 796 women and one out of 266 of the men had sex with their uncles and only one of the 266 boys had sex with their aunts. That corresponds to a rate of 2% for uncles~nieces, 0.3% for uncles~nephews, and 0.3% for aunts~nephews.

Overall

Given that:

• 15-25% of people have a sexual experience with a sibling.

• 10-25% of people have a sexual experience with a cousin.

• 0.5% to 5% of fathers have sex with their daughters.

• 1% to 3% of nieces have sex with an uncle.

• 0.1% to 0.5% of men have sex with their aunts/uncles.

• 0.1% to 0.01% of men have sex with their fathers/mothers

Assuming independence between these events, the prevalence of incest in the West is at least 25% and at most 53%. 53% seems rather implausible, which leads me to believe that I am overestimating the degree to which people dishonestly report incest or that there are substantial violations of independence between these events. The lower limit in this case seems to be closer to the truth.

Based on one of the tables Finkelhor provided, it does not appear that violations of independence are that stark: a total of 77 experiences were reported in 60 men, and the 151 women reported a total of 194 incestuous relationships. The fact that some people report multiple relationships does not necessarily indicate that independence is violated, though from what we know about the heritability of fertility and sexual behaviour the null hypothesis of statistical independence cannot be true.

The fact that women report more incestuous experiences suggests to me that the prevalence of incest is not biased upwards by false self-reports; men are more likely to make things up on a survey. Also, reports of parent/child incest are very rare, which would not be expected if false reports of incestuous activity were common in surveys.