Estimating Effect Sizes
In most models for the effect sizes of vector control, there is a parameter describing vector control coverage. The effects of vector control in the models occur because the presence of vector control has modified one or more of the mosquito blood feeding or demographic parameters: the overall blood feeding rate \(f\); the human fraction, \(q\); the mosquito mortality rate, \(g\); or mosquito dispersal, through the emigration rate \(\sigma\) or one of the associated parameters.
There is a difference between the parameter describing coverage in models and the measures of coverage used by malaria programs.
Operational – Programmatic definitions of coverage describe quantities that are relevant for operations:
for IRS, the fraction of houses sprayed;
for bed nets, some measure of ownership and use.
Contact – Vector control effects are related to the fraction of potential encounters in which a mosquito comes into contact with the pesticide / device and modified mosquito bionomics:
for IRS, it is the fraction of times a mosquito lands and rests on a sprayed surface, making contact with the residual pesticide, after blood feeding; or it could represent the fraction of times a mosquito avoids entering a house because of IRS.
for bed nets, it is the fraction of times a mosquito attempts to approach a human only to have the encounter blocked by a net; ITN models could also stipulate whether the contact involves exposure to insecticide that would increase mosquito mortality.
In developing a quantitative understanding of vector control in context, we fix some aspects of malaria control, including coverage as defined operationally, and measures of effects given contact as defined by the model. The parameter we fit translates operational measures of coverage into contact-based measures of coverage.