But wait, I have more good news: Those estimates are probably not optimistic enough. The Technical Panel on Assumptions and Methods established by the Social Security Advisory Board, an independent government agency that advises Social Security’s trustees on matters including actuarial assumptions, says Social Security is systematically underestimating future declines in mortality rates, and therefore underestimating the likely life spans of young Americans. (Demographic estimates, of course, are necessary to project future revenues and expenses for the program.)