The results of clinical trials may not be reflected in ordinary clinical practice. Strict regulation of the conditions under which trials occur may mean that both intervention and control groups are cared for in ways that are different from those that apply outside such trials. Standards of practice may be different in units that undertake clinical trials and may differ between trial and non-trial groups in the same units.

At McMaster University in Hamilton, Canada a trial of antithrombin treatment in premature infants with respiratory distress …