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Centre for Evidence-
Based Medicine

Was patient follow-up sufficiently long and complete?

Ideally, we'd like to see a follow-up period for a study that lasts until every patient recovers or has one of the other outcomes of interest, or until the elapsed time of observation is of clinical interest to clinicians or patients. If follow-up is short, it may be that too few study patients will have the outcome of interest, thus providing little information of use to a patient.

The more patients who are unavailable for follow-up, the less accurate the estimate of the risk of the outcome. Losses may occur because patients are too ill (or too well) to be followed or may have died, and the failure to document these losses threatens the validity of the study. Sometimes, however, losses to follow-up are unavoidable and unrelated to prognosis. Although an analysis showing that the baseline demographics of these patients are similar to those followed up provides some reassurance that certain types of participants were not selectively lost, such an analysis is limited by those characteristics that were measured at baseline. Investigators cannot control for unmeasured traits that may be important prognostically, and that may have been more or less prevalent in the lost participants than in the followed-up participants. most evidence-based journals of secondary publication (like ACP Journal Club and Evidence Based Medicine) require at least 80% follow-up for a prognosis study to be considered valid.

In the study we retrieved, follow-up was sufficiently complete and patients were followed from 2 to 6.5 years.

  1. Was a defined, representative sample of patients assembled at a common (usually early) point in the course of their disease?
  2. Was patient follow-up sufficiently long and complete?
  3. Were objective outcome criteria applied in a "blind" fashion?
  4. If subgroups with different prognoses are identified: