Sample size determination
PTSS
Sample size was guided by the need to enroll enough participants to examine the feasibility of recruiting, retaining, and assessing participants, and of implementing the FAID Fear intervention with good compliance in this population to inform the design of a fully powered RCT. Assuming retention rates of ~90%, a sample size of 15 participants would allow us to compute a 95% confidence interval around this estimate of 75%– 100%, providing sufficient precision for planning a larger trial. This study was not powered to detect significant effects of the intervention on mechanistic outcomes (i.e., cardiac fear, PTSS).