Monday, May 14, 2012

Sensitivity and Specificity: Examples from the Literature

Here are three examples of how sensitivity and specificity are used in the literature.

Kongsted A, Johannesen E, Leboeuf-Yde C. Feasibility of the STarT back screening tool in chiropractic clinics: a cross-sectional study of patients with low back pain. Chiropr Man Therap.2011 Apr 28;19:10.
The STarT back screening tool (SBT) allocates low back pain (LBP) patients into three risk groups and is intended to assist clinicians in their decisions about choice of treatment. The tool consists of domains from larger questionnaires that previously have been shown to be predictive of non-recovery from LBP. This study was performed to describe the distribution of depression, fear avoidance and catastrophising in relation to the SBT risk groups. A total of 475 primary care patients were included from 19 chiropractic clinics. They completed the SBT, the Major Depression Inventory (MDI), the Fear Avoidance Beliefs Questionnaire (FABQ), and the Coping Strategies Questionnaire. Associations between the continuous scores of the psychological questionnaires and the SBT were tested by means of linear regression, and the diagnostic performance of the SBT in relation to the other questionnaires was described in terms of sensitivity, specificity and likelihood ratios.In this cohort 59% were in the SBT low risk, 29% in the medium risk and 11% in high risk group. The SBT risk groups were positively associated with all of the psychological questionnaires. The SBT high risk group had positive likelihood ratios for having a risk profile on the psychological scales ranging from 3.8 (95% CI 2.3 - 6.3) for the MDI to 7.6 (95% CI 4.9 - 11.7) for the FABQ. The SBT questionnaire was feasible to use in chiropractic practice and risk groups were related to the presence of well-established psychological prognostic factors. If the tool proves to predict prognosis in future studies, it would be a relevant alternative in clinical practice to other more comprehensive questionnaires.

Leboeuf-Yde C, Rosenbaum A, Axén I, Lövgren PW, Jørgensen K, Halasz L, Eklund A, Wedderkopp N. The Nordic Subpopulation Research Programme: prediction of treatment outcome in patients with low back pain treated by chiropractors--does the psychological profile matter? Chiropr Osteopat. 2009 Dec 30;17:14

Background:  It is clinically important to be able to select patients suitable for treatment and to be able to predict with some certainty the outcome for patients treated for low back pain (LBP). It is not known to what degree outcome among chiropractic patients is affected by psychological factors.

Objectives:  To investigate if some demographic, psychological, and clinical variables can predict outcome with chiropractic care in patients with LBP.

Methods:  A prospective multi-center practice-based study was carried out, in which demographic, clinical and psychological information was collected at base-line. Outcome was established at the 4(th )visit and after three months. The predictive value was studied for all base-line variables, individually and in a multivariable analysis.

Results:  In all, 55 of 99 invited chiropractors collected information on 731 patients. At the 4(th )visit data were available on 626 patients and on 464 patients after 3 months. Fee subsidization (OR 3.2; 95% CI 1.9-5.5), total duration of pain in the past year (OR 1.5; 95% CI 1.0-2.2), and general health (OR 1.2; 95% CI 1.1-1.4) remained in the final model as predictors of treatment outcome at the 4(th )visit. The sensitivity was low (12%), whereas the specificity was high (97%). At the three months follow-up, duration of pain in the past year (OR 2.1; 95% CI 1.4-3.1), and pain in other parts of the spine in the past year (OR1.6; 1.1-2.5) were independently associated with outcome. However, both the sensitivity and specificity were relatively low (60% and 50%). The addition of the psychological variables did not improve the models and none of the psychological variables remained significant in the final analyses. There was a positive gradient in relation to the number of positive predictor variables and outcome, both at the 4(th )visit and after 3 months.

Conclusion:  Psychological factors were not found to be relevant in the prediction of treatment outcome in Swedish chiropractic patients with LBP.

Vanti C, Bonfiglioli R, Calabrese M, Marinelli F, Violante FS, Pillastrini P. Relationship between interpretation and accuracy of the upper limb neurodynamic test 1 in carpal tunnel syndrome. J Manipulative Physiol Ther. 2012 Jan;35(1):54-63. Epub 2011 Oct 27


Objective:  This prospective diagnostic test study evaluated the relationship between interpretation criteria and accuracy of the Upper Limb Neurodynamic Test 1 (ULNT1) in the diagnosis of carpal tunnel syndrome.

Methods: A blind comparison with a reference criterion of typical clinical presentation and abnormal median nerve conduction was used. All subjects were first tested with nerve conduction studies and then with ULNT1. Each examiner was blinded to the results collected by the other examiners.

Results: We analyzed 47 subjects and 84 limbs. Considering ULNT1 as positive in the presence of reproduction of symptoms only in the thumb or lateral 2 fingers, we estimated sensitivity to be equal to 40% (95% confidence interval [CI], 0.256-0.564), specificity 79.59% (95% CI, 0.664-0.885), positive predictive value 58.33% (95% CI, 0.388-0.755), negative predictive value 65% (95% CI, 0.524-0.758), positive likelihood ratio 1.96 (95% CI, 1.275-3.012), and negative likelihood ratio 0.7538 (95% CI, 0.490-1.159). Considering the increase of symptoms with contralateral or decrease of symptoms with ipsilateral cervical side bending as mandatory positivity criterion, specificity improved, but sensitivity decreased.

Conclusion: Our investigation suggests that the reproduction of symptoms in the thumb or lateral 2 fingers of the affected arm during ULNT1 has weak diagnostic accuracy for carpal tunnel syndrome.

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