Assessing the short term impact of air pollution on mortality: a matching approach

Table 1 Covariates balance before and after matching, Milan, Italy, 2003–2006

^aTemperature: average temperature in the current and in the previous 3 days
^bHeat episodes: days with temperatures exceeding 28 °C. Summer days: from May 1st to September 30th
^cWheeler and Watson’s statistics (W) for the comparison of the distribution of the circular variable “day of the year” between treated and control units (pre-matching W) or between treated and matched controls (post-matching W)
^dStandardized difference: pre-matching (\( {\delta}^{pre} \)) and post-matching (\( {\delta}^{post} \))
^e% bias: \( 100\times \left({\delta}^{pre}-{\delta}^{post}\right)/{\delta}^{pre} \)
^fPercent reduction in the Wheeler and Watson’s statistics after matching

ISSN: 1476-069X