OBJECTIVEUsing case-crossover design to estimate the acute effect of ambient air pollution on daily mortality in Shanghai, and to explore the applicability of if in studying the acute health effects of air pollution.

METHODSCase-crossover technique was used to evaluate the relationship between air pollution and daily mortality from June 2000 to December 2001 in Shanghai. The results of the bi-directional control sampling approach were compared with unidirectional approach.

RESULTSThe validity of relative risks in case-crossover studies varied greatly depending on the strategy used in control sampling. When a bi-directional six control sampling approach was used an increase of relative risk of non-accident mortality on each 10 micro g/m(3) over a 48-hr moving average of PM(10), SO(2) and NO(2) corresponds to 1.003 (95% CI: 1.001 - 1.005), 1.016 (95% CI: 1.011 - 1.021), and 1.020 (95% CI: 1.012 - 1.027) respectively was seen.

CONCLUSIONThe results reinforced the deleterious role of current air pollution level on human health in Shanghai, and provided information on the applicability of case-crossover design in studying the acute health effects of air pollution.