Calidad de un estudio: escala de Jadad

Quality of Study:
A numerical score between 0-5 is assigned as a rough measure of study design/reporting quality (0 being weakest and 5 being strongest). This number is based on a well-established, validated scale developed by Jadad et al. (Jadad AR, Moore RA, Carroll D, et al. Assessing the quality of reports of randomized clinical trials: is blinding necessary? Controlled Clinical Trials 1996;17[1]:1-12). This calculation does not account for all study elements that may be used to assess quality (other aspects of study design/reporting are addressed in the “Evidence Discussion” sections of monographs).

  • A Jadad score is calculated using the seven items in the table below. The first five items are indications of good quality, and each counts as one point towards an overall quality score. The final two items indicate poor quality, and a point is subtracted for each if its criteria are met. The range of possible scores is 0 to 5.

Jadad Score Calculation  
Item Score
Was the study described as randomized (this includes words such as randomly, random, and randomization)?
Was the method used to generate the sequence of randomization described and appropriate (table of random numbers, computer-generated, etc)?
Was the study described as double blind?
Was the method of double blinding described and appropriate (identical placebo, active placebo, dummy, etc)?
Was there a description of withdrawals and dropouts?
Deduct one point if the method used to generate the sequence of randomization was described and it was inappropriate (patients were allocated alternately, or according to date of birth, hospital number, etc).
Deduct one point if the study was described as double blind but the method of blinding was inappropriate (e.g., comparison of tablet vs. injection with no double dummy).

P = pending verification.

Magnitude of Benefit:
This summarizes how strong a benefit is: small, medium, large, or none. If results are not statistically significant “NA” for “not applicable” is entered. In order to be consistent in defining small, medium, and large benefits across different studies and monographs,
Natural Standard defines the magnitude of benefit in terms of the standard deviation (SD) of the outcome measure. Specifically, the benefit is considered:

  • Large: if >1 SD
  • Medium: if 0.5 to 0.9 SD
  • Small: if 0.2 to 0.4 SD

P = pending verification.In many cases, studies do not report the standard deviation of change of the outcome measure. However, the change in the standard deviation of the outcome measure (also known as effect size) can be calculated, and is derived by subtracting the mean (or mean difference) in the placebo/control group from the mean (or mean difference) in the treatment group, and dividing that quantity by the pooled standard deviation (Effect size=[Mean Treatment – Mean Placebo]/SDp).

About Ruben Roa

Medico especialista en Medicina Familiar. Magister en Epidemiologia, Economia de la Salud, Felowship en Medicina Familiar. Ex-Secretario Ejecutivo Confederación Iberoamericana de Medicina Familiar, miembro del Board de Educación Médica Continua WONCA. Senior Research at Agencia de Tecnologias Santiarias ISALUD.
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