Estimating counterfactual treatment outcomes over time through adversarially balanced representations

Ioana Bica, Ahmed M. Alaa, James Jordon, Mihaela van der Schaar

International Conference on Learning Representations (ICLR) 2020

Code Author: Ioana Bica (ioana.bica95@gmail.com)

Introduction

The Counterfactual Recurrent Network (CRN) is a causal inference method for estimating the effects of treatments assigned over time from observational data. CRN constructs treatment invariant representations at each timestep in order to break the association between patient history and treatment assignments and thus removes the bias from time-dependent confounders present in observational datasets. By performing counterfactual estimation of future treatment outcomes, CRN can be used to answer critical medical questions such as deciding when to give treatments to patients, when to start and stop treatment regimes, and also how to select from multiple treatments over time. We illustrate in the following figure the applicability of our method in choosing optimal cancer treatments.

Model architecture

CRN consists of an encoder network which builds treatment invariant representations of the patient history that are used to initialize the decoder. The decoder network estimates outcomes under an intended sequence of future treatments, while also updating the balanced representation. The model architecture is illustrated in the following figure:

Dependencies

The model was implemented in Python 3.6. The following packages are needed for running the model:

• numpy==1.18.2
• pandas==1.0.4
• scipy==1.1.0
• scikit-learn==0.22.2
• tensorflow-gpu==1.15.0

Running and evaluating the model:

Since in real datasets counterfactual outcomes and the degree of time-dependent confounding are not known, we evaluate the CRN on a Pharmacokinetic-Pharmacodynamic model of tumour growth, which uses a state-of-the-art bio-mathematical model to simulate the combined effects of chemotherapy and radiotherapy in non-small cell lung cancer patients (Geng et al., Nature Scientific Reports 2017). The same simulation model was used by Lim et al., NeurIPS 2018. We adopt their implementation from: https://github.com/sjblim/rmsn_nips_2018 and extend it to incorporate counterfactual outcomes.

The chemo_coeff and radio_coeff in the simulation specify the amount of time-dependent confounding applied to the chemotherapy and radiotherapy treatment assignments in the generated observational dataset. The results in the paper were obtained by varying the chemo_coeff and radio_coeff, and thus obtaining observational datasets with different amounts of time-dependent confounding.

Figure 4 in our paper illustrates the results for gamma = chemo_coeff = radio_coeff in {1, 2, 3, 4, 5} for both one-step-ahead prediction and sequence prediction (five-step-ahead prediction) of counterfactual outcomes.

To train and evaluate the Counterfactual Recurrent Network on observational datasets for tumour growth, run the following command with the chosen command line arguments.

python test_crn.py

Options :
        --chemo_coeff	                     # Parameter controlling the amount of time-dependent confounding applied to the chemotherapy treatment assignment. 
	--radio_coeff	                     # Parameter controlling the amount of time-dependent confounding applied to the radiotherapy treatment assignment.
	--results_dir                        # Directory for saving the results.
	--model_name                         # Model name (used for saving the model).
	--b_encoder_hyperparm_tuning         # Boolean flag for performing hyperparameter tuning for the encoder. 
	--b_decoder_hyperparm_tuning         # Boolean flag for performing hyperparameter tuning for the decoder. 

Outputs:

• root mean squared error (RMSE) for one-step-ahead prediction of counterfactual outcomes.
• RMSE for five-step-ahead prediction of counterfactual outcomes.
• Trained encoder and decoder models.

The synthetic dataset for each setting of chemo_coeff and radio_coeff is over 1GB in size, which is why it is re-generated every time the code is run.

Example usages

To test the Counterfactual Recurrent Network, run (this will use a default settings of hyperparameters):

python test_crn.py --chemo_coeff=2 --radio_coeff=2 --model_name=crn_test_2

To perform hyperparameter optimization and test the Counterfactual Recurrent Network, run:

python test_crn.py --chemo_coeff=2 --radio_coeff=2 --model_name=crn_test_2 --b_encoder_hyperparm_tuning=True --b_decoder_hyperparm_tuning=True

For the results in the paper, hyperparameter optimization was run (this can take about 8 hours on an NVIDIA Tesla K80 GPU).

Reference

If you use this code, please cite:

@article{bica2020crn,
  title={Estimating counterfactual treatment outcomes over time through adversarially balanced representations},
  author={Bica, Ioana and Alaa, Ahmed M and Jordon, James and van der Schaar, Mihaela},
  journal={International Conference on Learning Representations},
  year={2020}
}