Jadad scale
The Jadad scale, sometimes known as Jadad scoring or the Oxford quality scoring system, is a procedure to independently assess the methodological quality of a clinical trial
Clinical trial
Clinical trials are a set of procedures in medical research and drug development that are conducted to allow safety and efficacy data to be collected for health interventions...

. It is the most widely used such assessment in the world, and as of 2008, its seminal paper has been cited in over 3000 scientific works.

The Jadad scale is named after Alejandro Jadad-Bechara
Alejandro R. Jadad Bechara
Alejandro Jadad is a physician, educator, researcher and public advocate, whose mission is to help improve health and wellness for all, through information and communication technologies.Dr...

, a Colombian physician who worked as a Research Fellow at the Oxford Pain Relief Unit, Nuffield Department of Anaesthetics, at the University of Oxford
University of Oxford
The University of Oxford is a university located in Oxford, United Kingdom. It is the second-oldest surviving university in the world and the oldest in the English-speaking world. Although its exact date of foundation is unclear, there is evidence of teaching as far back as 1096...

. Jadad and his team outlined their views of the effectiveness of blinding on published studies in a 1996 paper in the Journal of Controlled Clinical Trials. An appendix to the paper described a scale allocating trials a score of between zero (very poor) and five (rigorous).

Jadad felt that the randomised controlled trial was of great importance for the advancement of medical science, describing it in a 2007 book as "one of the simplest, most powerful and revolutionary forms of research".


Clinical trials are conducted for the purpose of collecting data on the efficacy of medical treatments. The treatment might be, for example, a new drug
A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...

, a medical device
Medical device
A medical device is a product which is used for medical purposes in patients, in diagnosis, therapy or surgery . Whereas medicinal products achieve their principal action by pharmacological, metabolic or immunological means. Medical devices act by other means like physical, mechanical, thermal,...

, a surgical procedure, or a preventative regime. Clinical trial protocol
Clinical trial protocol
A clinical trial protocol is a document that describes the objective, design, methodology, statistical considerations, and organization of a clinical trial...

s vary considerably depending on the nature of the treatment under investigation, but typically in a controlled trial researchers gather a group of volunteers and subject some to the test treatment, while giving the others either no treatment (known as a placebo
A placebo is a simulated or otherwise medically ineffectual treatment for a disease or other medical condition intended to deceive the recipient...

), or an established treatment for comparison. After a defined time period, the patients in the test group are assessed for health improvements in comparison with the control group.

However, trials can vary greatly in quality. Methodological errors such as poor blinding or poor randomisation allow factors such as the placebo effect
Placebo effect
Placebo effect may refer to:* Placebo effect, the tendency of any medication or treatment, even an inert or ineffective one, to exhibit results simply because the recipient believes that it will work...

 or selection bias
Selection bias
Selection bias is a statistical bias in which there is an error in choosing the individuals or groups to take part in a scientific study. It is sometimes referred to as the selection effect. The term "selection bias" most often refers to the distortion of a statistical analysis, resulting from the...

 to adversely affect the results of a trial.


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. Studies have indicated, for example, that nonrandomised trials are more likely to show a positive result for a new treatment than for an established conventional one.


The importance of scientific control
Scientific control
Scientific control allows for comparisons of concepts. It is a part of the scientific method. Scientific control is often used in discussion of natural experiments. For instance, during drug testing, scientists will try to control two groups to keep them as identical and normal as possible, then...

s to limit factors under test is well established. However, it is also important that none of those involved in a clinical trial, whether the researcher, the subject patient or any other involved parties, should allow their own prior expectations to affect reporting of results. The placebo effect
Placebo effect
Placebo effect may refer to:* Placebo effect, the tendency of any medication or treatment, even an inert or ineffective one, to exhibit results simply because the recipient believes that it will work...

 is known to be a confounding factor in trials; affecting the ability of both patients and doctors to report accurately on the clinical outcome. Experimental blinding is a process to prevent bias
Bias is an inclination to present or hold a partial perspective at the expense of alternatives. Bias can come in many forms.-In judgement and decision making:...

, both conscious and subconscious, skewing results.

Blinding frequently takes the form of a placebo
A placebo is a simulated or otherwise medically ineffectual treatment for a disease or other medical condition intended to deceive the recipient...

, an inactive dummy that is indistinguishable from the real treatment. Blinding can however be difficult to achieve in some trials, for example, surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...

 or physical therapy
Physical therapy
Physical therapy , often abbreviated PT, is a health care profession. Physical therapy is concerned with identifying and maximizing quality of life and movement potential within the spheres of promotion, prevention, diagnosis, treatment/intervention,and rehabilitation...

. Poor blinding can exaggerate the perceived effects of treatment, particularly if any such effects are small. Blinding should be appropriate to the study, and is ideally double blind, wherein neither the patient nor doctor is aware of whether they are in the control or test group, eliminating any such psychological effects from the study.

Withdrawals and dropouts

Withdrawals and dropouts
Dropping out
Dropping out means leaving a group for either practical reasons, necessities or disillusionment with the system from which the individual in question leaves....

 are those patients who fail to complete a course of treatment, or fail to report back on its outcome to the researchers. The reasons for doing so might be varied: the individuals may have moved away, abandoned the course of treatment, or died. Whatever the reason, the attrition rate can skew results of a study, particularly for those subjects who ceased treatment due to perceived inefficacy. In smoking cessation
Smoking cessation
Smoking cessation is the process of discontinuing the practice of inhaling a smoked substance. This article focuses exclusively on cessation of tobacco smoking; however, the methods described may apply to cessation of smoking other substances that can be difficult to stop using due to the...

 studies, for example, it is routine to consider all dropouts as failures.

Jadad questionnaire

In an appendix to their 1996 paper, Jadad et al. published a three-point questionnaire that formed the basis for a Jadad score. Each question was to be answered with either a yes or a no. Each yes would score a single point, each no zero points; there were to be no fractional points. The Jadad team stated that they expected it should take no longer than ten minutes to score any individual paper. The questions were as follows:
  1. Was the study described as randomized?
  2. Was the study described as double blind?
  3. Was there a description of withdrawals and dropouts?

To receive the corresponding point, an article should describe the number of withdrawals and dropouts, in each of the study groups, and the underlying reasons. Additional points were given if:
  • The method of randomisation was described in the paper, and that method was appropriate.
  • The method of blinding was described, and it was appropriate.

Points would however be deducted if:
  • The method of randomisation was described, but was inappropriate.
  • The method of blinding was described, but was inappropriate.

A paper reporting a clinical trial could therefore receive a Jadad score of between zero and five. The Jadad scale is sometimes described as a five-point scale, though there are only three questions.


Jadad scores may be used in a number of ways:
  1. To evaluate the general quality of medical research in a particular field.
  2. To set a minimum standard for the paper's results to be included in a meta analysis. A researcher conducting a systematic review
    Systematic review
    A systematic review is a literature review focused on a research question that tries to identify, appraise, select and synthesize all high quality research evidence relevant to that question. Systematic reviews of high-quality randomized controlled trials are crucial to evidence-based medicine...

    for example might elect to exclude all papers on the topic with a Jadad score of 3 or less.
  3. For critical analysis of an individual paper.


The Jadad scale is not without its critics, who have charged that it is flawed, being over-simplistic, placing too much emphasis on blinding, and can show low consistency between different raters.

Jadad has accepted these criticisms, and even questions the value of quality assessments of clinical trials, as much as he questions the assessment of quality of online medical information.
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