  How much do individuals contribute to team output? I propose an econometric
framework to quantify individual contributions when only the output of their
teams is observed. The identification strategy relies on following individuals
who work in different teams over time. I consider two production technologies.
For a production function that is additive in worker inputs, I propose a
regression estimator and show how to obtain unbiased estimates of variance
components that measure the contributions of heterogeneity and sorting. To
estimate nonlinear models with complementarity, I propose a mixture approach
under the assumption that individual types are discrete, and rely on a
mean-field variational approximation for estimation. To illustrate the methods,
I estimate the impact of economists on their research output, and the
contributions of inventors to the quality of their patents.
