Читать книгу Evidence in Medicine - Iain K. Crombie - Страница 29

The type of patient lost to follow‐up is possibly more important than the number lost. If more seriously ill patients are lost, and this loss happens to a greater extent in one of the treatment groups, then substantial bias can occur. Thus when loss to follow‐up occurs, trials need to report not just the magnitude of loss, but the number and characteristics of the patients lost from each of the treatment arms.

Trials that report the overall loss to follow‐up often do not give the data separately for intervention and control groups. One study of trials in leading medical journals found that 20% did not report the numbers missing in the treatment and control groups separately [42]. However a more recent study found that leading journals had improved, with only 3% of trials failing to report this information [45]. Another study of trials in palliative care found that 13% did not report the numbers lost to follow‐up in both treatment arms [51]. In these studies it is not clear whether treatment effects will be biased by differential loss to follow‐up.

Reporting of the types of patients lost to follow‐up is often poor. In one review, 91% of trials did not compare the characteristics of those lost to follow‐up with those successfully followed up [43]. Among 108 trials in palliative care, none compared the intervention and control groups for the baseline characteristics of those with missing outcome data [47]. Thus it is often not possible to assess whether those lost to follow‐up in the intervention group differ from those lost in the control group.