Median 24-hour mortality with samples of bioassayed nets collected after 14-20 and 26-32 months. Nets were tested in bioassays with both susceptible and wild caught mosquitoes. N = 28 for three to six month nets; N = 44 for 14-20 month nets; N = 40 for 26-32 month nets. The plots show median, 25th and 75th percentile (box) and fifth and 95% percentile (whisker) of the per cent mortality. Susceptible strain = Anopheles arabiensis Nazareth colony tested in Ethiopia; Wild-caught = adults reared from larvae collected in Sodere, Oromia province, Ethiopia in November 2008 and 2009 (at 14-20 months and 26-32 months respectively).