Читать книгу Evidence in Medicine - Iain K. Crombie - Страница 27

In a trial, patients are followed up for a defined period to determine the effect of treatment. During this time period some patients can withdraw from the study, and contact can be lost with others, so that the outcome is often not measured on all patients. A rule of thumb for losses to follow‐up is that <5% loss is unlikely to cause bias and that >20% loss is serious, with those between 5% and 20% being potentially problematic [40, 41].