Figure 4From: Air pollution and emergency department visits for cardiac and respiratory conditions: a multi-city time-series analysis Percent increase in emergency department visits for selected pollutants, diagnostic groups per mean pollutant concentration. (Point estimates and 95% confidence intervals are shown by number of knots in natural spline functions of time; from left to right, base analysis where number of knots is optimized separately in each city, and knots every 3, 5 and 17 weeks).Back to article page