in a country which keeps more health stats on its citizens (one with national health care)-they already have the mechanisms to do so--where people are easier to follow because they move less (less immigration, emigration, loss to followup), such as a Scandinavian country.
Here is a study based on stats of over 1.5 million women!!!:
http://www.breastcancersource.com/br...93_0_0_0.aspx?