Читать книгу Evidence in Medicine - Iain K. Crombie - Страница 31

A difficult issue for the analysis of a trial is how to cope with those who are lost to follow‐up. The accepted approach to this problem is termed ‘intention to treat’. This holds that all patients should be analysed in the groups to which they were randomised, no matter what subsequently happened to them. Intention to treat is regarded as ‘a key defence against bias’ in clinical trials [52].

A popular technique to handle missing data is complete case analysis, which restricts the analysis to those successfully followed up. This approach was used in 26% of trials on musculoskeletal disorders [53], in 45%–54% of studies in general medicine [45, 54] and in 60% of trials in palliative care [51]. Despite its popularity, complete case analysis clearly contravenes the principle of intention to treat, effectively losing the benefit of randomisation. This method is likely to introduce bias, because the number and types of patients lost to follow‐up are unlikely to be the same in the intervention and control groups [55].