A study by Loha and colleges in Plos One looked at the effect of IRS and ITNs in a village in Southern Ethiopia:
The level of ITN utilization increased after mass distribution of ITNs; however it did not lower the risk for malaria clustering. Therefore, it is possible that free mass distribution of ITNs is not an effective tool with which to combat malaria without follow-up to ensure the optimal utilization of the ITNs.
Of course, there are several studies showing the effect of bed net usage on community malaria incidence, but there is a lack of studies showing the effectiveness of ITNs dependent on the involved vector. In the study are Anopheles arabiensis is the dominant vector, a mosquito which feed indoor as well as outdoor, and possibly before people go to bed.