Identification of complier and noncomplier average causal effects in the presence of latent missing-at-random (LMAR) outcomes: a unifying view and choices of assumptions

The study of treatment effects is often complicated by noncompliance and missing data. In the one-sided noncompliance setting where of interest are the complier and noncomplier average causal effects, we address outcome missingness of the latent missing at random type (LMAR, also known as latent ignorability). That is, conditional on covariates and treatment assigned, the missingness may depend on compliance type. Within the instrumental variable (IV) approach to noncompliance, methods have been proposed for handling LMAR outcome that additionally invoke an exclusion restriction-type assumption on missingness, but no solution has been proposed for when a non-IV approach is used. This article focuses on effect identification in the presence of LMAR outcomes, with a view to flexibly accommodate different principal identification approaches. We show that under treatment assignment ignorability and LMAR only, effect nonidentifiability boils down to a set of two connected mixture equations involving unidentified stratum-specific response probabilities and outcome means. This clarifies that (except for a special case) effect identification generally requires two additional assumptions: a specific missingness mechanism assumption and a principal identification assumption. This provides a template for identifying effects based on separate choices of these assumptions. We consider a range of specific missingness assumptions, including those that have appeared in the literature and some new ones. Incidentally, we find an issue in the existing assumptions, and propose a modification of the assumptions to avoid the issue. Results under different assumptions are illustrated using data from the Baltimore Experience Corps Trial.

Good intentions and ICH-GCP: Trial conduct training needs to go beyond the ICH-GCP document and include the intention-to-treat principle

BACKGROUND

It is assumed investigators and statisticians fully understand the importance of avoiding missing outcomes and the intention-to-treat principle during design and analysis phases of a randomised controlled trial in order to obtain the most valuable and reliable results. However, many personnel undertaking day-to-day trial conduct and data collection commonly rely exclusively for guidance on the widely implemented, indeed regulated, International Conference on Harmonisation-Good Clinical Practice document as the guideline and standard for trial conduct.

PURPOSE

This article describes adverse consequences of omission of intention-to-treat principles from training for trial personnel and explores the need for training in addition to the International Conference on Harmonisation-Good Clinical Practice guideline document.

METHODS

Data from the Breast Boost Study were used to illustrate a comparison of actual results, where vigilant senior investigators re-enforced intention-to-treat requirements throughout all aspects of trial conduct with results that could easily have occurred if study personnel did not understand the importance of intention-to-treat principles. Experience as a co-ordinating centre for an international trial (Trans-Tasman Radiation Oncology Group 08.06 Breast STARS) acted as an audit of data-management culture regarding intention-to-treat in Australia and New Zealand.

RESULTS

Despite the Breast Boost Study exceeding planned accrual, it was demonstrated that the study, which found a statistically significant result, could have reported a negative or inconclusive result under the scenario of trial conduct personnel having lack of understanding of the importance of avoiding losses to follow-up. Trans-Tasman Radiation Oncology 08.06 co-ordination experience verified that data-management culture in Australia and New Zealand does not adequately recognise intention-to-treat principles, and this is reflected in trial conduct.

LIMITATIONS

Trial data described are limited to two trials and in the Australian and New Zealand setting.

CONCLUSION

To be both scientifically and ethically valid, guidelines for trial conduct should include and stress the importance of the intention-to-treat principle and in particular avoiding missing outcomes. Our discussion highlights the vitally important role played by personnel involved in day-to-day trial conduct. Inclusion of scientific principles in guideline documents and/or training which goes beyond International Conference on Harmonisation-Good Clinical Practice to include intention-to-treat is essential to achieve robust research results. Related aspects of randomised trial consent and ethics are discussed.