7  Cheatsheet

In this chapter, we provide an overview of the main functionalities of the fect package, including the required inputs, available plot types, key options, and testing capabilities across various methods.

7.1 Methods

Inputs for fect(methods = "___")

Method Model for \(\hat{Y}(0)\) References
fe Standard two-way fixed effects model Liu, Wang & Xu (2022), Borusyak, Jaravel & Spiess (2024)
ife Interactive fixed effects model Gobillon & Magnac (2016), Xu (2017)
mc Matrix completion method Athey et al. (2021)
polynomial Two-way fixed effects model with unit-specific trends –
cfe “Complex” or multi-level fixed effects –
gsynth Interactive fixed effects model Xu (2017)

7.2 Plot Types

Inputs for plot(fect_object, type = "___")

Type Description Applicable Methods
box Box plot of ATT by period. fe, ife, mc, gsynth, polynomial, cfe
calendar CATT by calendar time. fe, ife, mc, gsynth, polynomial, cfe
heterogenous or hte CATT by a covariate. fe, ife, mc, gsynth, polynomial, cfe
counterfactual or ct Observed vs. imputed outcome for treated units. fe, ife, mc, gsynth
equiv Pretreatment residuals with equivalence intervals. fe, ife, mc, gsynth, polynomial, cfe
exit Period-wise ATT relative to treatment exit. fe, ife, mc, polynomial, cfe
factors Estimated factors (factor-based methods). ife, gsynth
gap or es Event-study plot: ATT by pre- and post-treatment periods. fe, ife, mc, gsynth, polynomial, cfe
loadings Estimated factor loadings (factor-based methods). ife, gsynth
status Treatment status by period for all units. fe, ife, mc, gsynth, polynomial, cfe
sens Rambachan & Roth (2023) sensitivity analysis for treatment effects. fect_sens() function applied to fe, ife, mc, gsynth, polynomial, cfe
sens_es Event-study sensitivity analysis for treatment effects. fect_sens() function applied to fe, ife, mc, gsynth, polynomial, cfe
cumul Cumulative treatment effects over time. effect() function applied to fe, ife, mc, gsynth, polynomial, cfe

7.3 Tests as Options

Inputs for fect(...)

Input Description Applicable Methods
loo Leave-one-period-out goodness-of-fit test (TRUE/FALSE). fe, ife, mc, gsynth
carryoverTest Tests for carryover effects in post-treatment periods (TRUE/FALSE). fe, ife, mc
carryover.period Range of post-treatment periods for the carryover test (vector). fe, ife, mc
permute Permutation test (TRUE/FALSE). fe, ife, mc, gsynth
m Block length for permutation test (m=2 by default). fe, ife, mc, gsynth
CV Cross-validation for factor-based methods. ife, mc, gsynth

7.4 Required and Optional Inputs

A check mark (✓) indicates that the method requires or accepts the input.

7.4.1 Required Inputs

Input fe ife mc gsynth polynomial cfe
Y (outcome) ✓ ✓ ✓ ✓ ✓ ✓
D (treatment) ✓ ✓ ✓ ✓ ✓ ✓
X (covariates) ✓ ✓ ✓ ✓ ✓ ✓
data ✓ ✓ ✓ ✓ ✓ ✓
index (unit & time IDs) ✓ ✓ ✓ ✓ ✓ ✓
sfe (simple additive FEs) – – – – – ✓
cfe (complex FEs) – – – – – ✓

7.4.2 Optional Inputs

Input fe ife mc gsynth polynomial cfe
W (weight) ✓ ✓ ✓ ✓ ✓ ✓
se (uncertainty) ✓ ✓ ✓ ✓ ✓ ✓
nboots (# bootstrap reps) ✓ ✓ ✓ ✓ ✓ ✓
force (FE structure) ✓ ✓ ✓ ✓ ✓ ✓
lambda(Hyper-parameter sequence) – – ✓ ✓ – –
nlambda(Length of hyper-parameter sequence) – – ✓ ✓ – –
r (# factor) – ✓ – ✓ – –
k ( # cross-validation rounds) – ✓ ✓ ✓ – –
degree (degree of the interacted fixed effects) – – – – ✓ –

7.4.3 Important Options

Input Options Applicable Methods
force Fixed effects structure: “none”, “unit”, “time”, “two-way” (default) fe, ife, mc, poly, cfe, gsynth
vartype (when method = "gsynth") Uncertainty estimator: “parametric” (default), “bootstrap”, “jackknife” gsynth
vartype (otherwise) Uncertainty estimator: “bootstrap” (default), “jackknife” fe, ife, mc, polynomial, cfe
criterion Model selection criterion: “mspe” (default), “gmspe”, “moment”, “pc”. ife, mc, polynomial, cfe, gsynth

7.5 Notes

  • Most methods share core inputs (Y, D, X, data, index).

  • Method polynomial and cfe allow either “jackknife” or “bootstrap” for uncertainty estimates.

  • Factor-based methods (ife, gsynth) can use rand k for factor selection and cross validation. We can implement a similar process using mc or gsynth with lambda andnlambda.

  • carryoverTest and loo are available in fe, ife, mc, polynomial, and cfe but not in gsynth.

  • force allows various levels of fixed effects ("none", "unit", "time", "two-way").

  • fect includes several built-in values for optional arguments that often require an integer or boolean input. All boolean arguments (such as parallel, se, or CV) are set to FALSE by default to speed up computation. Below is a complementary table listing parameters that require numeric inputs.

Inputs Description Default
degree The degree of the interacted fixed effects(int) 2
nboots Number of bootstrap runs (int) 200
k Sets the number of cross-validation rounds(int) 10
r Sets the number of factors 0; c(0,5) when CV
m Specifies the block length for the permutation test 2
nlambda Length of hyper-parameter sequence 10
  • With an integer input for nlambda, fect can randomly generate appropriate hyper-parameter sequence.

Enjoy using fect!