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cluster randomized trials

Tools of the Trade: Intra-cluster correlations

David McKenzie's picture

In clustered randomized experiments, random assignment occurs at the group level, with multiple units observed within each group. For example, education interventions might be assigned at the school level, with outcomes measured at the student level, or microfinance interventions might be assigned at the savings group level, with outcomes measured for individual clients.

Beware of studies with a small number of clusters

Berk Ozler's picture

While some of us get to conduct individually randomized trials, I’d say that cluster randomized trials are pretty much the norm in field experiments in economics. Add to that the increase in the level of ambition we recently acquired to have interventions with multiple treatment arms (rather than one treatment and one control group) and mix it with a pinch of logistical and budgetary constraints, we have a non-negligible number of trials with small numbers of clusters (schools, clinics, villages, etc.).

Designing experiments to measure spillover effects

Berk Ozler's picture

Many programs affect those who were not directly targeted by the intervention. We know this for medical interventions (e.g. deworming: Kremer and Miguel 2004); cash transfer programs (e.g. PROGRESA: Angelucci and de Giorgi 2009); and now voter awareness programs (Giné and Mansuri 2011).