atts <- att_gt(
  yname = "y", # LHS variable
  tname = "year", # panel time variable
  idname = "id", # firms' panel id variable
  gname = "treat_date", # first treatment period variable
  data = baker, # data
  xformla = NULL, # no covariates
  #xformla = ~ l_police, # with covariates
  est_method = "ipw", # "dr" is doubly robust. "ipw" is inverse probability weighting. "reg" is regression
  control_group = "notyettreated", # set the comparison group which is either "nevertreated" or "notyettreated" 
  bstrap = TRUE, # if TRUE compute bootstrapped SE
  biters = 1000, # number of bootstrap iterations
  print_details = FALSE, # if TRUE, print detailed results
  base_period="universal", # long-differences
  clustervars = "state", # cluster level
  panel = TRUE # whether the data is panel or repeated cross-sectional
)