Not all studies use the same definition of sexual assault. Surveys in particular are subject to question wording and question order effects. As army1987 notes, the ~20% proportion is for sexual assault, not just rape.
Keep in mind that the object-level question here is whether a rape-reporting rate of 12% can possibly be consistent with a ~20% sexual assault rate. Will (and the media in general) misstated the class of events to which the “12%” referred; Will then stated that it could not possibly be the case that the 12% and the 20% were consistent. This is a very strong claim, which means that checking/refuting it is easy in absolute terms. To refute the argument, it is not necessary to have precise estimates—it is only necessary to show that the statistics being reported are broadly consistent.
Not all studies use the same definition of sexual assault. Surveys in particular are subject to question wording and question order effects. As army1987 notes, the ~20% proportion is for sexual assault, not just rape.
Keep in mind that the object-level question here is whether a rape-reporting rate of 12% can possibly be consistent with a ~20% sexual assault rate. Will (and the media in general) misstated the class of events to which the “12%” referred; Will then stated that it could not possibly be the case that the 12% and the 20% were consistent. This is a very strong claim, which means that checking/refuting it is easy in absolute terms. To refute the argument, it is not necessary to have precise estimates—it is only necessary to show that the statistics being reported are broadly consistent.