Example Experiments Mosquito nets and malaria in India

Example Experiments Mosquito nets and malaria in India 1

Tarozzi et al. (2011) “Micro-loans, Insecticide-Treated Bednets and Malaria: Evidence from a randomized controlled trial in Orissa (India)” • Effect of subsidizing mosquito nets (treated with insecticide) on the incidence of malaria. • Experimental design at the village level. 2

“Treatment” • Villages assigned to 3 groups: – Free bednets – Subsidized bednets (micro loans) – Control group • Intervention in October/November 2007 • Later interviews about usage, and health tests (December 2008 -April 2009). 3

Analysis • 141 villages out of 900, sample of 1, 800 families (about 15 per village). • Effect of offering subsidized loans (X) on: – Acquisition and use of bednets (Y 1) – Malaria incidence (Y 2) • Differences estimator • (Dif in diffs) • With controls 4

Randomization test • Check that villages in the three groups are “the same” (W’s) • Income level, malaria incidence, previous use of bednets, etc. • Test for differences in means. 5

Differences estimator Yi = a + b 1 Freei + b 2 MFi + ui Difference-in-differences DYi = a + b 1 Freei + b 2 MFi + ui (with controls) 6

Results (“*” indicates significance at 5%) 7

Results (“*” indicates significance at 5%) 8

Results (“*” indicates significance at 5%) 9

Results (“*” indicates significance at 5%) 10

Results (“*” indicates significance at 5%) 11

Results (“*” indicates significance at 5%) 12

Threats to internal validity • Failure to randomize? • Imperfect compliance? • Attrition? – 4%, similar in all 3 groups • Experimental effects? • Small sample? 13

Threats to external validity • Non-representative sample? – Random sample of 900 villages with presence of BISWA (? ). • Non-representative treatment? • General equilibrium effects? – Probably! • Treatment versus eligibility? – Think! 14