Most of our scientific information about human sexuality has been obtained through:

I believe the answer is: Surveys

Surveys is a form of data gathering method that allow the subjects to fill in a set of questionnaires freely regarding a certain topic. This method allows the researchers to obtain large number of subjects for their researches, and the subjects could have a feeling of secrecy since the answering could be done in private settings.

answer; (true);

you would times this by how many days there are in a year 365*400=$146000