"Women lie so we can't trust self reports on past sexual history."

This is called social desirability bias, a form of self report or response bias. It may occur any time research participants want to give a favorable impression.

Does the science support that "women lie" about sexual history? Two questions: do we see self report bias and, if so, is the magnitude of that bias meaningful (large)?

Jaccard et al (2004, "Recalling Sexual Partners: The Accuracy of Self-reports") tested this question directly using what is called a bogus-pipeline: a fake polygraph. The response distributions were equal in the pipeline and the standard anonymous survey condition:

For example, in a pilot study for this research, we compared response distributions for weekly reports of sexual behavior for: (a) respondents who were given self-administered questionnaires with instructions that stressed honest l responding and guaranteed confidentiality, with (b) a group of respondents given the same instructions but who were led to believe that they were being monitored with a lie detector test as they answered questions (see Jaccard & Wan, 1995, for details). Following traditional bogus-pipeline methodology, it was assumed that individuals who thought they were being physiologically monitored for lying were truthful in their responses. If the response distributions in the two groups are comparable, then this suggests that those in the standard instruction condition are being truthful. This was indeed the case. Thus, given complete confidentiality, incentive to respond truthfully and privacy of responding, most individuals will be truthful about their sexual activity.

In the main study, Jaccard et al. added an independent measure of social desirability bias itself. This acts as another way to detect skewed responses due to social desirability bias. They found no correlation between social desirability bias and any sexual self report measure:

A measure of social desirability response tendency was obtained at the one-month recall and, consistent with our pilot research, showed no significant correlation with any of the major variables reported here.

A third measure of accuracy in assessing self report bias for sexual history was added in the Jaccard et al. study: longitudinal recall. This is called test-retest validation. Participants reported sexual history on a weekly basis. If they were able to accurately recall sexual events at a future date consistent with past reports, this was taken as further evidence of truthful reporting.

Jaccard et al. then compared the distributions of self reported sexual partners to an external measure of distributions: the distributions were the same. Assuming spurious reporting, we should not see consistent and repeated distributions of self reported history across data sets.

Four separate techniques were used in the Jaccard et al. validation to rule out self report and desirability bias.

When a discrepancy was detected, the magnitude was small: a deviation of one sexual partner.

We see the same in the following study, when a discrepancy is detected between groups it is only in a small number of people and has a small magnitude:

"Social Desirability Bias in Sexual Behavior Reporting: Evidence from an Interview Mode Experiment in Rural Malawi." Kelly et al. 2004.

This study leveraged the previous findings that desirability bias usually occurs in face to face conversations, when it occurs. Subjects were given either a face to face interview or an anonymous computer based self assessment.

Only men self reported sexual history differently in the two conditions.

The same for this research review of sexual behavior in HIV-positive individuals. Even in groups where the social stigma is much larger than merely being sexually promiscuous the magnitude of discrepancy is small - when it exists at all.

"Reliability and validity of self-report measures of HIV-related sexual behavior: progress since 1990 and recommendations for research and practice."

Wrapping up:

At the moment we don't have a strong reason to believe that "women lie" on self report measures of sexual history. If/when they do, it is both rare in sample groups and the magnitude of the lie is small enough (1-2 people) that it should not influence most statistics on sexual history in a meaningful way.

Anyone who says we can't trust self reports due to bias needs to demonstrate the bias and its effect size. The existing validation research on sexual history self reporting does not support the claim that this is a common or large problem.

Edit: Additional study.

u/rivertorain- posted another study in the comments using the bogus-pipeline (fake lie detector) methodology. The results were very similar to the first Jaccard et al. study I posted: there was no significant sex difference for reporting of sexual partner history.

Also, in addition to not being significant, the magnitude of difference was only one partner between the bogus pipeline and anonymous survey condition. The same magnitude found in the Jaccard et al. study for test-retest validity.

Truth and Consequences: Using the Bogus Pipeline to Examine Sex Differences in Self-Reported Sexuality