placebo_in_time: In-Time Placebo (Backdating) Test for SCM

In coresynth: Fast and Unified Synthetic Control Methods

In-Time Placebo (Backdating) Test for SCM

Description

Re-estimates the synthetic control after artificially backdating the treatment to a pre-treatment period, following Abadie, Diamond & Hainmueller (2015) and Abadie & Vives-i-Bastida (2022, principle 7: "out-of-sample validation is key"). Only pre-treatment data enter the exercise, so the placebo gap after t0_placebo is uncontaminated by the actual intervention. A credible design shows no sizable divergence at the backdated treatment time.

Usage

placebo_in_time(fit, t0_placebo = NULL)

Arguments

fit	A sharp coresynth object from scm_fit() with method = "scm".
t0_placebo	Backdated treatment period as a 1-based position in fit$times; must satisfy ⁠2 <= t0_placebo < T_pre⁠. Default floor(T_pre / 2).

Details

The refit uses the outcomes of periods ⁠1..t0_placebo⁠ as predictors (the predictors = NULL default), regardless of how the original fit was specified, because user-supplied pred() windows cannot be lagged automatically (ADH 2015 lag their predictors by hand).

Value

A list with:

• t0_placebo: the backdated treatment period used

• times: time values of the pre-treatment window

• unit_weights: placebo donor weights

• Y_treat, Y_synth, gap: series over the pre-treatment window

• placebo_att: mean placebo gap over ⁠(t0_placebo, T_pre]⁠

• fit_rmspe: RMSPE over the placebo fitting window ⁠1..t0_placebo⁠

• eval_rmspe: RMSPE over the placebo post window ⁠(t0_placebo, T_pre]⁠

See Also

mspe_ratio_pval() for in-space placebos, loo_donors() for donor-robustness checks.

coresynth documentation built on Aug. 28, 2026, 1:06 a.m.