A Critic of Retrospective Multicenter Studies in Clinical Trichology.

Currently, retrospective multicenter studies have gained particular popularity with trichologists, and become a practice of some groups of authors for cranking up the number of papers on their resumes. Multicenter collaboration can result in higher rates of patient enrolment than single-center trials, thereby generating larger studies of shorter duration, while offering the opportunity for networking. A single-center trial is conducted according to a single protocol and at a single site, while multicenter trials are conducted according to a single protocol but at different locations, and conducted by various researchers. Differences between the two include variations in sample size, time of patient recruitment, costs, presence of bias, validity, and center and investigator characteristics. However, the validity of multicenter research can be questioned. A single center with a high number of patients, interventions, and large experience is superior to a collective of a large number of centers with low number of patients, interventions, and little experience at each center. Multicenter studies are at risk of inconsistent diagnosis and heterogeneity among centers and populations. Finally, by their nature, multicenter studies rely purely on local expert opinion to generate findings. If the centers participating in the study can be shown to be representative of the group or area of knowledge under study then content validity can be assumed. The practice though of selecting centers based on networking means there is a responsibility to prove and justify the selection procedures used. Hence, how a center is chosen for its competence is defined must be somewhat arbitrary, and the results would then represent that particular group's opinions at a given point in time. In conclusion, when interpreting results from retrospective multicenter clinical research, bias and traps among the result should be detected according to who performs it, which inclusion indication criteria is involved, what the target is, and how it is carried out.