bvu                     Bonus vetus OLS (BVU)
bvw                     Bonus vetus OLS (BVW)
ddm                     Double Demeaning (DDM)
discard_unusable        Discard non-positive and/or non-finite
                        observations in datasets
ek_tobit                Eaton and Kortum (2001) Tobit model (EK Tobit)
et_tobit                Eaton and Tamura (1995) threshold Tobit model
                        (ET Tobit)
fixed_effects           Fixed Effects
gpml                    Gamma Pseudo Maximum Likelihood (GPML)
gravity_no_zeros        Gravity dataset without zero trade flows
gravity_zeros           Gravity dataset without zero trade flows
hm_summary              Head and Mayer consistent summary statistics
log_distance            Apply logarithm to distance column
nbpml                   Negative Binomial Pseudo Maximum Likelihood
                        (NBPML)
nls                     Non-linear Least Squares (NLS)
ols                     Ordinary Least Squares (OLS)
ppml                    Poisson Pseudo Maximum Likelihood (PPML)
sils                    Structural Iterated Least Squares (SILS)
tetrads                 Tetrads
tobit                   Left-censored Tobit model with known threshold
