Dear Professor Mean, I need to establish validity and reliability of a new measurement. How do I do this?
Dear Reader, validity and reliability are two very dangerous words to use, because they mean different things to different people. Here are some issues to consider.
Face validity is the extent to which your measurement appears valid to the general public. Does the measurement make intuitive sense? A closely related concept is content validity, the extent to which your measurement makes intuitive sense to a group of experts in the area.
Construct validity is establishing that you are measuring what you think you are measuring. You do this in two very different ways. First you establish that your measure correlates well with what it should correlate well with (convergent validity) and is uncorrelated with what it should be uncorrelated with (discriminant validity).
Criterion validity is the extent to which your measurement correlates with a gold standard. You can establish this two ways. First, you can see if your measure predicts a future measure that indicates the same thing (predictive validity). Second, you can see if your measure correlates well with other concurrent measures which have been established as gold standards.
Two large hospitals in the Netherlands studied four risk assessment scales for pressure ulcers (BMJ 2002; 325: 797 (12 October)). Four separate scales were applied to patients without pressure ulcers who were expected to stay at least five days in the hospital. These patients were then followed for up to 12 weeks to see if a pressure ulcer did develop. They showed that all four scales had poor predictive validity–they were unable to make accurate predictions of which patients would develop pressure ulcers. The authors noted that there had been minimal evaluation of these scales beyond expert opinion and literature review.
Prospective cohort study of routine use of risk assessment scales for prediction of pressure ulcers. Lisette Schoonhoven, Jeen R E Haalboom, Mente T Bousema, Ale Algra, Diederick E Grobbee, Maria H Grypdonck, and Erik Buskens. BMJ 2002; 325: 797. Available in html format or pdf format.
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The Examination Chapter of the Neurology section of the Family Practice Notebook, http://www.fpnotebook.com, has some interesting tests like the mini-mental state exam that could serve as good examples of developing validity.
Psychology Learning Resources. Internal Validity Tutorial. Available in html format.
http://www.sar.bolton.ac.uk/ltl/Workbooks/ex_p6.htm The Cochrane Group defines internal validity as “the extent to which the observed effects are true for the people in a study” – http://www.cochrane.dk/cochrane/handbook/hbookValidity.htm
J Psychosom Res 2002 Feb;52(2):69-77. The validity of the Hospital Anxiety and Depression Scale. An updated literature review. Bjelland I, Dahl AA, Haug TT, Neckelmann D.
J Cardiopulm Rehabil 2002 May-Jun;22(3):184-91. Validation of the Cardiovascular Limitations and Symptoms Profile (CLASP) in chronic stable angina. Lewin RJ, Thompson DR, Martin CR, Stuckey N, Devlen J, Michaelson S, Maguire P.Psychosomatics 2001 Sep-Oct;42(5):423-8. Sensitivity and specificity of observer and self-report questionnaires in major and minor depression following myocardial infarction. Strik JJ, Honig A, Lousberg R, Denollet J.
Disabil Rehabil 2001 Nov 10;23(16):737-44. Screening for anxiety, depressive and somatoform disorders in rehabilitation–validity of HADS and GHQ-12 in patients with musculoskeletal disease. Harter M, Reuter K, Gross-Hardt K, Bengel J.
You can find an earlier version of this page on my original website.