There is uncertainty in reported trial outcomes

Trial results may be difficult to interpret because of large uncertainty (wide confidence intervals) in the outcome measures. Trials may not have been powered specifically to detect differences in patient-relevant endpoints such as health-related quality of life. In some healthcare systems, secondary and tertiary outcomes may be considered to be lower quality evidence. High levels of uncertainty may be reported if there are lower rates of the outcome event than expected. Results for subgroups of importance to the health system of interest will have greater uncertainty, and in some cases may not have been reported.