Fig. 4
From: Assessing the short term impact of air pollution on mortality: a matching approach
![Fig. 4](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs12940-017-0215-7/MediaObjects/12940_2017_215_Fig4_HTML.gif)
Number of times each control day is selected as a matched control, Milan, Italy, 2003–2006
From: Assessing the short term impact of air pollution on mortality: a matching approach
Number of times each control day is selected as a matched control, Milan, Italy, 2003–2006