| castle | Data from Cheng and Hoekstra (2013) | 
| df_het | Simulated data with two treatment groups and heterogenous effects | 
| df_hom | Simulated data with two treatment groups and homogenous effects | 
| did2s | Calculate two-stage difference-in-differences following Gardner (2021) | 
| event_study | Estimate event-study coefficients using TWFE and 5 proposed improvements. | 
| gen_data | Generate TWFE data | 
| plot_event_study | Estimate event-study coefficients using TWFE and 5 proposed improvements. |