“…Several cohort and case-control studies of outdoor air pollution have been reported (Stocks and Campbell, 1955;Hammond and Horn, 1958a/b;Haenszel et al, 1962;Haenszel and Taeuber, 1964;Dean, 1966;Hitosugi, 1968;Hammond, 1972;Cederlo¨f et al, 1975;Dean et al, 1977Dean et al, , 1978Pike et al, 1979;Hammond and Garfinkel, 1980;Doll and Peto, 1981;Vena, 1982;Tenkanen et al, 1985;Brownson et al, 1987;Samet et al, 1987;Tenkanen and Teppo, 1987;Xu et al, 1989;Jedrychowski et al, 1990;Holowaty et al, 1991;Katsouyanni et al, 1991;Mills et al, 1991;Jo¨ckel et al, 1992;Dockery et al, 1993;Tenkanen, 1993;Barbone et al, 1995;Pope et al, 1995;Zaridze et al, 1995;Biggeri et al, 1996;Engholm et al, 1996;Pawlega et al, 1997;Beeson et al, 1998;Abbey et al, 1999;McDonnell et al, 2000;Nyberg et al, 2000;Hoek et al, 2002;Pope et al, 2002). Overall, the studies suggest relative risks (RRs) of up to about 1.5 for urban vs rural residence or high vs low estimated air pollution exposure.…”