 A final but very important issue is that of the external validity of the RCT results. Even under ideal conditions (i.e., when medical researchers have very strong reasons to presume the assumptions under which an RCT works to be satisfied), the RCT can only establish that the treatment is effective in the test population. Typical test populations differ from the target populations (i.e., those populations for whom the treatment has been developed and who will eventually receive the treatment) in more or less systematic ways. For example, many RCTs will exclude elderly patients or patients with co-morbidities but the treatment will be marketed to these patients. For financial reasons, many RCTs are nowadays conducted in developing countries whereas the treatments are mainly or exclusively marketed to patients in developed countries. Whereas the protocols for conducting an RCT are very strict and detailed, there are no good guidelines how to make treatment decisions when the patient at hand belongs to a population that differs from the population in which the RCT was conducted (e.g., Cartwright 2011).