indexes time. This model has a full set of time effects, t, a full set of group effects, g, group/time period covariates, xgt (these are the policy variables), individual-specific covariates, zigt, unobserved group/time effects, vgt, and individual-specific errors, uigt. We are interested in estimating . ∙ As in cluster sample cases, can write
yigt gt zigtgt uigt, i 1, . . . , Mgt,
which shows a model at the individual level where both the intercepts and slopes are allowed to differ across all g, t pairs. Then, we think of gt as
gt t g xgt vgt.
We can think of (7) as a regression model at the group/time period level.