A function to calculate average outcomes for units in their pre-treatment periods (this function can also be used to recover pre-treatment averages of covariates, etc.). For units that do not participate in the treatment (and therefore have group==0), the function calculates their overall average outcome.
Arguments
- df
the data.frame used in the function
- idname
name of column that holds the unit id
- yname
name of column containing the outcome (or other variable) for which to calculate its outcome in the immediate pre-treatment period
- tname
name of column that holds the time period
- gname
name of column containing the unit's group