Table 1 Dates of exposure and control periods
Exposure Period | Control Period 1 (Preceding) | Control Period 2 (Following) |
|---|---|---|
June 19–21, 2012 | May 29–31, 2012 | July 10–12, 2012 |
July 20–22, 2011 | June 29–July 1, 2011 | Aug 17–19, 2011 |
July 5–7, 2010 | June 14–16, 2010 | Aug 2–4, 2010 |