Clinical trial participants who are randomized to treatment and have a baseline value but no post-baseline data pose a unique challenge. These patients need to be included to preserve randomization. However, there is no information about the outcome or the intercurrent events that led to missing data. Composite and hypothetical strategies can accommodate participants with no post-baseline data. The present study investigated common methods based on hypothetical strategies in example data sets and in a simulation study. Because there is no information about the treatment effect when there is no post-baseline data, it is not surprising that various models yielded similar results. In simulated data, treatment contrasts were not biased when the reason for missing all post-baseline data was random, treatment related, or outcome related. Bias occurred only when missingness was treatment and outcome related, and arose from a missing not at random mechanism. The bias was not large. The maximum Type I error rate across all scenarios and methods was 6.4%. Imputing no change for missing data at the first postbaseline visit and assuming missing at random for all other missing values yielded a maximum Type I error rate of 5.1%. Given the idiosyncratic nature of clinical trials, no universally best analytic approach exists for dealing with participants that have a baseline but no post-baseline data. Analysts can choose among these methods to provide an approach tailored to the situation at hand.

The authors have declared no competing interest.

This study did not receive any funding

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

All data produced in the present study are available upon reasonable request to the authors