After an ongoing study since 1976 by Francine Godstein, from the Harvard School of Public Health in Boston to 12,000 nurses, has been found and recorded systematically.
Baada ya utafiti unaoendelea tangu mwaka 1976 na Francine Godstein, kutoka Shule ya Harvard ya Afya ya Umma katika Boston kwa wauguzi 12,000, imekuwa kupatikana na kumbukumbu utaratibu.