format
A dataframe made up of 8 units: 1 treated (no 7) and 7 control (no. 2,7,13,17,29,32,36,38)
, 3 predictors (X1, X2, X3), 21 time periods (1980 - 2000), a unit.names.variable column ("names") and an outcome variable column (Y). All columns have column names.