We are barraged by time-to-intervention studies (door-to-balloon time, time-to-antibiotics, door-to-needle, etc.). However, it must be kept in mind that these studies are purely correlational in design. Such studies cannot prove causation and, at best, are only hypothesis generating. Frequently they are downright misleading. Time-to-intervention is an extremely complex variable which reflects properties of the patient, the health-care system, and their mutual interactions. This complexity yields multiple sources of confounding. Below are some examples of confounding variables which typically plague these studies.

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