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Two studies can report the same complication percentage despite very different follow-up durations. Late events absent from short observation may appear later. Appraisal should explain the observation horizon and population retained alongside the outcome itself.
Scope of the decision
Distinguish planned follow-up from time actually completed. A mean or median alone does not describe the distribution of early losses. Assess how well available data cover the period relevant to the device’s particular benefit and risk question.
Worked review
For example, a report directly compares event percentages from a six-month study and a three-year study. The reviewer makes different exposure periods and follow-up losses visible. Without a suitable analysis, a lower short-term percentage is not interpreted as superior long-term safety. The contribution of each dataset is bounded by its observation period.
Practical checks
- Record planned and actual follow-up together with the relevant population.
- Assess effects of early withdrawal and missing follow-up on interpretation.
- State appropriate methods and limitations when comparing different horizons.
Acceptance and limits
Acceptance requires interpretation of time horizons consistent with the claim. Longer follow-up does not automatically mean better quality; retention and measurement also matter. A long-term evidence gap should not be treated as resolved merely because short-term findings are favourable.
Frequently asked questions
- Does the same event percentage mean the same risk?
- Not directly when observation periods or populations differ.
- Is median follow-up sufficient?
- It is a useful summary, but relevant distribution and loss-to-follow-up details also need assessment.