first of all that link is an american study. OP was talking about canada.

Second, that link doesn't mention 6%.

Third, they mention that based on the available data, they can't estimate the actual number of under reported cases, they just suspect that it is low.

The most accurate counts of rape and sexual assault cannot be achieved without measuring them separately from other victimizations, the report says. It recommends that BJS develop a separate survey for measuring rape and sexual assault.

the purpose of that study was to show how future data on the topic could be gathered, but does not state that said data has actually been gathered

This report examines issues such as the legal definitions in use by the states for these crimes, best methods for representing the definitions in survey instruments so that their meaning is clear to respondents, and best methods for obtaining as complete reporting as possible of these crimes in surveys, including methods whereby respondents may report anonymously.

care to try again?