How is Freddie Mac's Primary Mortgage Market Survey conducted?

Freddie Mac's Primary Mortgage Market SurveySM (PMMS^SM) has evolved into the foremost reliable, representative source of mortgage rate trends and is relied upon by the mortgage industry and the public in gauging market conditions and evaluating mortgage loan options. Since April 1971, Freddie Mac has surveyed lenders across the nation weekly to determine average mortgage rates. Currently, 125 lenders are surveyed each week and the mix of lender types—thrifts, commercial banks and mortgage lending companies—is roughly proportional to the level of mortgage business that each type commands nationwide. The survey results are published extensively in the media, used in several government agency reports, and many other industry-related publications.