“Friends that Matter: How Social Influence Drives Attention in Social Media”
With Sean J. Westwood
Social media is becoming an increasingly important channel by which political news and opinion reaches the public. This work shows how the strength of the relationship between the sharer and the viewer has a powerful effect on selectivity in the realm of traditional news and opinion content in social media. It relies on a Facebook application that utilizes the OpenGraph framework to construct an experimentally controlled replica of the Facebook newsfeed interface, providing unparalleled ecological validity. By randomizing the assignment of articles to be recommended by weak- or strong-tie Facebook contacts, it dissociates social influence from interest-homophily as the causal factor responsible for this effect.
Estimating Heterogeneous Treatment Effects and the Effects of Heterogeneous Treatments with Ensemble Methods
With Justin Grimmer and Sean J. Westwood
Randomized experiments are increasingly used to study political phenomena because they can credibly estimate the average effect of a treatment on a population of interest. But political scientists are often interested in how effects vary across sub-populations- heterogeneous treatment effects-and how differences in the content of the treatment affects responses-the response to heterogeneous treatments. Several new methods have been introduced to estimate heterogeneous effects, but it is difficult to know if a method will perform well for a particular data set. Rather than use only one method, we show how an ensemble of methods—weighted averages of estimates from individual models-accurately measure heterogeneous effects. Building on a large literature on ensemble methods, we show the close relationship between out of sample prediction and accurate estimation of heterogeneous treatment effects and demonstrate how pooling models leads to superior performance to individual methods across diverse problems. We apply the ensemble method to two experiments, illuminating how constituents reward and punish legislators for particularistic spending.