Real World Studies: What They Are and What They Are Not.

Patients are filtered by rigorously defined study selection criteria for recruitment into research; this is necessary to improve signal detection, improve internal validity, reduce study-related risks, and meet ethical standards. Research patients are assessed and managed in ways that differ from usual practice. So, neither patients nor the treatment environment resembles everyday patients treated in everyday practice. This diminishes the generalizability of study findings; that is, their external validity. There is, therefore, an increasing trend to conduct "real-world studies." In this context, "real-world patients" are those who are not filtered by restrictive study selection criteria, and "real-world settings" are those in which patients are managed with few study-related guidelines and restrictions. The elephant in the room is that the glamour associated with such real-world studies is an illusion. This is because real-world patients in one real-world setting can differ widely from real-world patients in another real-world setting. So, even in real-world studies, we can only generalize study findings to the population from which the sample was drawn and the setting in which the sample was managed. As a final note, many assessments in research, such as computerized or pen-and-paper neuropsychological tests, are not real-world measures as are, for example, measures of activities of daily living or quality of life.