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published in the British Medical Journal, somewhat whimsically points out
that EBM should not require the suspension of common sense and good
judgment. The authors do make a serious point, however. The rationale
outlined below for the need for RCTs to demonstrate the effectiveness of
parachutes has been applied to many interventions in medicine.
OBSERVATIONAL DATA ARE INFERIOR TO RCT DATA: Hormone replacement therapy (HRT) use appeared to lower coronary heart disease (CHD) risk in observational studies; The Women's Health Initiative (an RCT) showed that HRT raises CHD (and many other) risks.
NATURAL HISTORY OF GRAVITATIONAL CHALLENGE: If failure to use a parachute resulted in 100% mortality, that might be evidence of effectiveness. However, survival from falls of 33,000 feet have been documented. Furthermore, parachutes have been associated with morbidity and mortality. Therefore RCTs are needed to determine the balance of risks and benefits.
OBSERVATIONAL STUDIES ARE SUBJECT TO SELECTION AND REPORTING BIAS: Those jumping from airplanes without parachutes are likely to have pre-existing psychiatric morbidity. Individuals who jump with parachutes may have less mental illness and differ in other characteristics such as socioeconomic status and cigarette smoking. Thus, there may be a healthy cohort effect, in play.