tests/testthat/test-difference-in-differences.R

In rdddr: Companion Datasets and Functions for Blair, Coppock, and Humphreys (2022) "Research Design: Declare, Diagnose, Redesign"

test_that("lag_by_group and did_multiplegt_tidy work", {

  skip_if_not_installed("DIDmultiplegt")

  library(dplyr)
  library(DeclareDesign)
  library(DIDmultiplegt)

  N_units <- 20
  N_time_periods <- 20

  declaration_16.3 <-
    declare_model(
      units = add_level(
        N = N_units,
        U_unit = rnorm(N),
        D_unit = if_else(U_unit > median(U_unit), 1, 0),
        D_time = sample(1:N_time_periods, N, replace = TRUE)
      ),
      periods = add_level(
        N = N_time_periods,
        U_time = rnorm(N),
        nest = FALSE
      ),
      unit_period = cross_levels(
        by = join_using(units, periods),
        U = rnorm(N),
        potential_outcomes(Y ~ U + U_unit + U_time + D * (0.2 - 1 * (D_time - as.numeric(periods))), conditions = list(D = c(0, 1))),
        D = if_else(D_unit == 1 & as.numeric(periods) >= D_time, 1, 0),
        D_lag = lag_by_group(D, groups = units, n = 1, order_by = periods)
      )
    ) +
    declare_inquiry(
      ATT = mean(Y_D_1 - Y_D_0),
      subset = D == 1
    ) +
    declare_inquiry(
      ATT_switchers = mean(Y_D_1 - Y_D_0),
      subset = D == 1 & D_lag == 0 & !is.na(D_lag)
    ) +
    declare_measurement(Y = reveal_outcomes(Y ~ D)) +
    declare_estimator(
      Y ~ D, fixed_effects = ~ units + periods,
      .method = lm_robust,
      inquiry = c("ATT", "ATT_switchers"),
      label = "twoway-fe"
    ) +
    declare_estimator(
      Y = "Y",
      G = "units",
      T = "periods",
      D = "D",
      handler = label_estimator(did_multiplegt_tidy),
      inquiry = c("ATT", "ATT_switchers"),
      label = "chaisemartin"
    )

  expect_error(suppressWarnings(simulate_design(declaration_16.3, sims = 1)), NA)

})