Determinants of treatment duration in the prevention of recurrent venous thromboembolism: a protocol for a balanced vignette experiment

Introduction Venous thromboembolism (VTE) is a condition that annually occurs in approximately 1% of the world's population. Patients who have already had a VTE are at elevated risk for a recurrent VTE. Recurrent events increase the risk of long-term sequelae and can be fatal. Adequate secondary prophylaxis is thus needed to prevent such events. Patients with VTE are often prone to bleeding, and pharmacological prophylaxis exacerbates bleeding risk. Expert opinions on the optimum duration of secondary prophylaxis in VTE still vary substantially. The existence of treatment guidelines has not led to uniformity of VTE secondary prophylaxis strategies, which means that physicians still adhere to individual risk calculi in determining treatment duration.

Methods and analysis The aim of this study is to establish what factors lie at the root of this variance in VTE secondary prophylactic treatment strategies, and what risk factors are deemed of particular importance in determining the perceived risks and benefits of variable treatment durations. To do this, we created a survey based on a D-efficient and G-efficient balanced experimental vignette design. This protocol covers all aspects of how this survey was set up and how it was implemented. The analysis of the experimental data will be carried out using mixed-effects methods, which are beneficial in scenarios with high interindividual variance and correlated (eg, repeated-measures) responses. We propose the use of maximal random effects structures insofar as possible.

Ethics and dissemination All data are de-identified, and any identifying characteristics of the respondents will not be reported in a final manuscript or elsewhere. A paper describing the expert interviews is currently under peer review. A manuscript that contains the analysis of the results of the experiment described in this protocol is being drafted, and will also be submitted to a peer-reviewed journal.