It is named after Canadian-Colombian physician Alex Jadad who in 1996 described a system for allocating such trials a score of between zero (very poor) and five (rigorous).
[1] The Jadad scale independently assesses the methodological quality of a clinical trial judging the effectiveness of blinding.
[2] In a 2007 book Jadad described the randomised controlled trial as "one of the simplest, most powerful and revolutionary forms of research".
[6] Randomisation is a process to remove potential distortion of statistical results arising from the manner in which the trial is conducted, in particular in the selection of subjects.
[7] The placebo effect is known to be a confounding factor in trials; affecting the ability of both patients and doctors to report accurately on the clinical outcome.
Whatever the reason, the attrition rate can skew results of a study, particularly for those subjects who ceased treatment due to perceived inefficacy.
The Jadad team stated that they expected it should take no longer than ten minutes to score any individual paper.
Critics have charged that the Jadad scale is flawed, being over-simplistic and placing too much emphasis on blinding,[16][17] and can show low consistency between different raters.