Potential impact of COVID-19 on ongoing clinical trials: a simulation study with the neurological Yale Global Tic Severity Scale based on the CANNA-TICS study

Pharm Stat. 2021 May;20(3):675-691. doi: 10.1002/pst.2100. Epub 2021 Feb 16.


The COVID-19 pandemic has manifold impacts on clinical trials. In response, drug regulatory agencies and public health bodies have issued guidance on how to assess potential impacts on ongoing clinical trials and stress the importance of a risk-assessment as a pre-requisite for modifications to the clinical trial conduct. This article presents a simulation study to assess the impact on the power of an ongoing clinical trial without the need to unblind trial data and compromise trial integrity. In the context of the CANNA-TICS trial, investigating the effect of nabiximols on reducing the total tic score of the Yale Global Tic Severity Scale (YGTSS-TTS) in patients with chronic tic disorders and Tourette syndrome, the impact of the two COVID-19 related intercurrent events handled by a treatment policy strategy is investigated using a multiplicative and additive data generating model. The empirical power is examined for the analysis of the YGTSS-TTS as a continuous and dichotomized endpoint using analysis techniques adjusted and unadjusted for the occurrence of the intercurrent event. In the investigated scenarios, the simulation studies showed that substantial power losses are possible, potentially making sample size increases necessary to retain sufficient power. However, we were also able to identify scenarios with only limited loss of power. By adjusting for the occurrence of the intercurrent event, the power loss could be diminished to different degrees in most scenarios. In summary, the presented risk assessment approach may support decisions on trial modifications like sample size increases, while maintaining trial integrity.

Keywords: COVID-19; Yale Global Tic Severity Scale; power; risk assessment; simulation study.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • COVID-19 / prevention & control*
  • COVID-19 / psychology
  • COVID-19 / transmission
  • Cannabidiol / adverse effects
  • Cannabidiol / therapeutic use*
  • Computer Simulation*
  • Data Interpretation, Statistical
  • Dronabinol / adverse effects
  • Dronabinol / therapeutic use*
  • Drug Combinations
  • Endpoint Determination
  • Humans
  • Mental Health*
  • Physical Distancing*
  • Randomized Controlled Trials as Topic* / statistics & numerical data
  • Research Design* / statistics & numerical data
  • Sample Size
  • Severity of Illness Index
  • Tic Disorders / diagnosis
  • Tic Disorders / drug therapy*
  • Tic Disorders / psychology
  • Tics / diagnosis
  • Tics / drug therapy*
  • Tics / psychology
  • Time Factors
  • Tourette Syndrome / drug therapy
  • Tourette Syndrome / psychology
  • Treatment Outcome


  • Drug Combinations
  • Cannabidiol
  • Dronabinol
  • nabiximols