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Centre for Evidence-
Based Medicine

Was follow-up of patients sufficiently long and complete?

We'd want to see that the duration of follow-up was sufficiently long to see the outcomes of interest. It is also important that the investigators provide details on the number of patients followed up and if possible, on the outcomes of patients who dropped out of the study. If we are unsure of what effect the dropouts may have on the study result, we can perform a 'sensitivity analysis' for a 'worst case scenario'. For the group that did better, assume that all the people who were lost to follow-up did poorly. For the group that did worse, assume all the people who were lost to follow-up fared well. If the result still supports the original conclusion, than the follow-up was sufficiently complete. It would be unusual for a study to be able to withstand more than a 20% loss of follow-up and therefore most journals of secondary publication (including ACP Journal Club and EBM) use this as an exclusion criteria for article selection.

From the abstract we identified in Best Evidence, 99.7%!! of patients were followed up for 5 years.

  1. Was the assignment of patients to treatment randomized? And, was the randomization list concealed?
  2. Was follow-up of patients sufficiently long and complete?
  3. Were all patients analyzed in the groups to which they were randomized?

    And some less important points:
  4. Were patients and clinicians kept blind to treatment?
  5. Were groups treated equally, apart from the experimental therapy?
  6. Were the groups similar at the start of the trial?