Medical books

Hi guys,

I would like to ask you one question . According to several medical books ( Descriptive Dictionary and Atlas of Sexology - Francoeur et al., 1991) penis lenght is between 5 to 7 inches. Do you know something more about the data in the medical books. How the authors of these books get these results. Does this information is based on facts. ( BPEL or NBPEL measurements , did they measure the patients or patients measured themselves and self-reported or the authors just collect the data from other sources like Kinsey report and repeat the data ).

Thanks a lot for any help!

Best regards