The PIs conducted a randomized field experiment to evaluate the use of network-based diffusion theory to select optimal farmers to train in the use of pit planting, a new agricultural technology to the area, so that knowledge and adoption of it are best spread through communities. The Malawian Ministry of Agriculture's current method of introducing and spreading new technologies was for an extension agent to select a "seed" farmer to train in the technology, and later encouraging the farmer to discuss it with neighbors. The PIs used the status quo method as a benchmark to test three different methods of selecting seed farmers using network-based diffusion theory.
The PIs chose to test threshold diffusion models, in which individuals adopt a new technology if they are connected to a tipping-point number of other adopters. Different formulations of the model yield different predictions of the best seed farmer in a given social network. The PIs focus on two versions of the threshold model. The first, a "simple contagion" model, only requires that an individual be connected to one other adopter to be induced to adopt also. In a simple contagion learning environment, seed farmers with the fewest redundant connections would be the most effective. The second, a "complex contagion" model, requires connections to multiple adopters to induce an individual to adopt as well. In a complex contagion learning environment, some level of redundant connections is desirable so that a threshold number of connected adopters is met.
The field experiment included four treatment arms. Two hundred Malawian villages were randomly assigned to have two seed farmers selected according to a simple contagion model, a complex contagion model, a second complex contagion model where geographic proximity is used as a proxy for connectedness (the "geo" model) , and the benchmark method of relying on extension agents to choose seed farmers. Optimal seeds in the threshold model villages were chosen using a social network census completed prior to the intervention for every sample village. The seed farmers were then trained to use pit planting to cultivate their fields.
The PIs found that the theory-driven selection of seed farmers led to greater diffusion of pit planting than the benchmark method, especially on the extensive margin (whether anyone adopts at all). This indicates that simply changing 'who' is trained based on network theory can increase adoption of new technologies. In addition, while the 'geo' treatment produces some gains relative to the benchmark, geographic proximity is a poor proxy for social network connectedness. Lastly, estimates suggest that a majority of people require more than one connection to an adopter to themselves adopt, indicating a complex contagion learning environment.