Dose-response studies in arthropod research usually involve observing and collecting successive information at different times on the same group of insects exposed to different concentrations of stimulus. When the same measure is collected repeatedly over time, the data become correlated and Probit Analysis technique which is the standard method in analyzing bioassay experiments data cannot be used. Lethal time is estimated when the speed of kill is of interest since mortality varies over time. We evaluate a complementary approach, repeated measures logistic regression using Generalized Estimating Equations (GEE), for lethal time determination in mosquito dose response. Mortality data from anopheles larva exposed to 3 botanical extracts (B,C,E) at 4 concentration levels: 500 mg/ml, 250 mg/ml, 50 mg/ml and 12.5 mg/ml were used. The result shows the estimated LT50 values with concentration 500 mg/ml being the most virulent chemical for extract B (LT50 = 10.3 hrs), C (LT50 = 7.2 hrs) and E (LT50 = 10.3 hrs). The least virulent chemical was concentration 12.5 mg/ml for extract B (LT50 = 52.1 hrs), C (LT50 = 70.7 hrs) and E (LT50 = 55.0 hrs). We conclude that repeated measures of logistic regression via GEE can be used as a tool to estimate LT50 more effectively in repeated measures of arthropod data.
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