add.n.r                 Add row numbers to regression result data.frame
add.pr                  Add approximate p-value based on t score or z
                        score, when sample size is large
add.sig                 Add significance level marks to the regression
                        result
check_cor               quickly check correlation matrix, or the
                        correlation between a particular X and all
                        other vars could be useful for looking for
                        relevant instrument
check_na_in             quickly check the proportion of NAs in each
                        columns of a dataframe
check_vif               quickly check the vifs in a regression model;
                        for checking multi-collinearity
combine_long_tab        Combine regression results from different
                        models by columns
compare_models          Compare regression models, which is compatible
                        with the reg.table output # updated 9/13/2018 #
cor.table               make the correlation matrix from the data.frame
                        used in regression
load.pkgs               load multiple packages
plot_effect             plotting the marginal effect of X on Y, with or
                        without one or multiple interaction terms
regrrr                  regrrr: a toolkit for compiling regression
                        results
scale_01                Scale a vector into the 0-1 scale
test_coef_equality      testing equality of two coefficients
                        (difference between coefficients of
                        regressors), a Wald test note: if v is not
                        alternatively specified, use
                        car::linearHypothesis(lm_model, "X1 = X2")
test_tilted_slopes      significance of regression slope (the marginal
                        effect) under moderation testing restriction:
                        the sig. of beta_x under the moderation of z1,
                        with or without additional interaction terms
                        (z2, z3, etc.)
to_long_tab             Convert the regression result to the long
                        format: the standard errors are in parentheses
                        and beneath the betas
