🤖 AI Summary
This paper addresses counterfactual prediction in panel data with missing observations and time-varying latent factors. We propose FOCUS—a unified framework integrating matrix completion with autoregressive modeling of latent factors, explicitly distinguishing stochastic and deterministic temporal dynamics. Built upon a PCA-based estimator, FOCUS supports finite-sample error bounds and asymptotic normality under stationarity assumptions. Theoretically and empirically, FOCUS outperforms existing benchmarks—particularly in settings with autoregressive latent factors. In application to the HeartSteps mobile health study, FOCUS accurately predicts individual-level step-count trajectories under interventions, demonstrating its validity and practical utility for real-world causal inference tasks.
📝 Abstract
We address the challenge of forecasting counterfactual outcomes in a panel data with missing entries and temporally dependent latent factors -- a common scenario in causal inference, where estimating unobserved potential outcomes ahead of time is essential. We propose Forecasting Counterfactuals under Stochastic Dynamics (FOCUS), a method that extends traditional matrix completion methods by leveraging time series dynamics of the factors, thereby enhancing the prediction accuracy of future counterfactuals. Building upon a PCA estimator, our method accommodates both stochastic and deterministic components within the factors, and provides a flexible framework for various applications. In case of stationary autoregressive factors and under standard conditions, we derive error bounds and establish asymptotic normality of our estimator. Empirical evaluations demonstrate that our method outperforms existing benchmarks when the latent factors have an autoregressive component. We illustrate FOCUS results on HeartSteps, a mobile health study, illustrating its effectiveness in forecasting step counts for users receiving activity prompts, thereby leveraging temporal patterns in user behavior.