The duration of protection provided by each product was tested
by means of arm-in-cage studies, in which volunteers insert their
repellent-treated arms into a cage with a fixed number of unfed
mosquitoes, and the elapsed time to the first bite is recorded. Testing
of repellents is usually conducted either in a laboratory or at
outdoor field sites.
14
Conducting such studies indoors makes it
possible to reduce potential confounding variables, such as wind
speed, temperature, humidity, density of the mosquito population,
the level of the mosquitoes’ hunger, and the species of the
mosquitoes, that can make it difficult to interpret comparisons
among products made in outdoor-field trials. We conducted our
tests with a low density of mosquitoes per cage rather than a high
density (some studies use more than 250 mosquitoes per cage)
because the low-density environment more accurately reflects the
typical biting pressures that are encountered during most outdoor
activities.