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January 15, 2012

What is the meaning of Reliability and Validity of a tool or an instrument? What are the methods to ensure them?

by pashtoonkasi

By Hrishikesh S. Kulkarni


It is the ability of a test or instrument to get a consistent estimate when repeated in a group of similar subjects. It is equivalent to repeatability.


It is the ability of a test or instrument to measure what it intended to measure. It is thus an estimate of the precision.


Methods to ensure reliability:


  • Test-retest reliability: The consistency of the instrument when it is administered multiple times by the same person.
  • Inter-observer reliability: The consistency of the instrument when it is administered by the different people.
  • Internal consistency: Internal consistency of an instrument occurs when the components of the instrument are found to appropriately measure the same concept being studied.
  • Cronbach alpha: It is a single-number estimate of how closely components of an instrument correlate with each other. It is obtained by computation.


Methods to ensure validity:


  • Construct validity: Construct validity ensures how well your concept or constructs actually translates into a functioning instrument. It is comprised of translation validity and criterion-related validity.
  • Translation validity: It identifies if your instrument is a good measure of your concept or construct. It comprises of face validity and content validity.
  • Face validity: The instrument, at an initial glance, appears to measure what it intendes to.
  • Content validity: If the content or the items in the questionnaire appropriately represent identify the concept being studied.
  • Criterion-related validity: It is a post-study analysis which demonstrates whether your instrument actually functions appropriately to identify the condition (or illness) based on your theory of the construct. This is done using factor analysis.


Of course, before embarking on the process of validation of a questionnaire/scale, always ensure someone hasn’t already validated the scale for your population. In such a case, you can directly start using it and the subsequent research becomes a lot simpler.


References and Further Reading:


[1] Madsen FA, Bruskewitz RC. Clinical manifestations of benign prostatic hyperplasia. Urol Clin North Am 1995;22:291-8.

[2] Folstein MF, Folstein SE, McHugh PR. “Mini-mental state”. A practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res. 1975; 12(3):189-98.

[3] Fass R, Longstreth GF, Pimentel M, et al. Evidence- and consensus-based practice guidelines for the diagnosis of irritable bowel syndrome. Arch. Intern. Med. 2000;161(17):2081–8.

[4] Leske SJ. Internal psychometric properties of the Critical Care Family Needs Inventory. Heart Lung 1991;20(3): 236-44.

[5] Azoulay E, Pochard F, Chevret S, Lemaire F, Mokhtari M, Le Gall JR, Dhainaut JF, Schlemmer B; French FAMIREA Group. Meeting the needs of intensive care unit patient families: a multicenter study. Am J Respir Crit Care Med. 2001;163(1):135-9.

[6] Trochim, William M. The Research Methods Knowledge Base, 2nd Edition. Internet WWW page. Available online at: Accessed May 16, 2009.

[7] Wasser T, Pasquale MA, Matchett SC, Bryan Y, Pasquale M. Establishing the reliability and validity of the Critical Care Family Satisfaction Survey. Critical Care Medicine 2001;29(1):192-6.

[8] Macey BA, Bouman CC. An evaluation of validity, reliability, and readability of the Critical Care Family Needs Inventory. Heart Lung 1991; 20(4):398-403.

[9] Bland JM, Altman DG. Statistics Notes: Validating scales and indexes. BMJ 2002;324:606-7.

[10] Dove Lane Quotes. Available:


From the Book; Research: What, Why and How? A treatise from Researchers to Researchers. 

Read more from Research Methods

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