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EVIDENCE ABOUT DIAGNOSTIC TESTS
Min H. Huang, PT, PhD, NCS
Diagnostic Tests
Test threshold and treatment threshold Help focus the exam in a particular body
region or system. Identify potential problems that require
referral to other health care providers. Assist in the diagnostic classification (i.e. a
specific practice pattern). Diagnostic tests MUST be reliable and valid.
Study Credibility
Appraisal of evidence begins with assessment of research validity.
Higher levels of validity indicate greater confidence that there is a lack of bias.
Lists of specific questions to ask (Table 10-1 in the textbook).
Specific Questions to ask
Can the research questions or hypotheses be tested with the research design
Did the investigators compare results from the diagnostic test to results from a “gold standard” diagnostic test
Were all subjects evaluated with the comparison diagnostic test
Were the individuals performing and interpreting each test’s result unaware of the other test’s results (i.e. were they masked, or blinded)
Specific Questions to ask
Did the investigators include subjects with all levels of stages of the condition being evaluated by the measure of interest
Did the investigators confirm their findings with a new set of subjects
Did the study use appropriate statistical analysis methods for reliability and validity Correlation coefficients Face, construct, criterion, concurrent validity
Were p values or C.I. significant?
Study Results
Sensitivity (SnNout) Specificity (SpPin) Positive predictive value (PPV) Negative predictive value (NPV) Likelihood ratios (LR):
reflect a diagnostic test’s ability to provide persuasive information
LR + = Sn/(1-Sp) LR – = (1-Sn)/Sp
Receiver Operating Characteristic Curves (ROC) a graphic way to evaluate different thresholds of a
test
Loong et al. (2003).
Sn = 24/30 = 80%
Sp = 56/70 = 80%
PPV = 24/38 = 63%
NPP = 56/62 = 90%
Figure 10-7: A Receiver Operating Characteristic (ROC) Curve for an Imperfect but Useful Test
Likelihood Ratio Nomogram
Use a nomogram to calculate posttest probability, i.e. the probability that the patient/client has the condition after a test result is obtained.
LR+ = 1-2, LR- = 0.5-1.0 negligible change in pretest probability
http://www.cebm.net/index.aspx?o=1043
EVIDENCE ABOUT CLINICAL MEASURES
Min H. Huang, PT, PhD, NCS
Clinical Measures
Are NOT used to label or classify a diagnosis or practice pattern
Quantify and/or describe a patient’s impairments in a standardized fashion
Distinguish among different levels of severity of a problem
Instruments must have reliability, validity, responsiveness
Study Credibility
SAME process as diagnostic tests Refer to questions in Table 10-2 Clinical measures MUST be validated in
patient populations with different diagnoses
Study Results
Reliability and validity are confirmed by correlation coefficients.
Responsiveness is commonly assessed by Minimal detectable change (MDC): the amount of
change that just exceeds the standard error of measurement
Standardized response mean (SRM): the ratio between the mean change score and the standard deviation of the change scores; reflect the change over time
Considerations for Implementing the Evidence into Practice
Test or measure should be available, practical and safe in the setting
Test or measure should have demonstrated performance on similar patient/clients
Can pretest probabilities be estimated for the patient/client
Patient/client’s preferences and values
Review
Most useful diagnostic tests and clinical measures have demonstrated reliability and validity
Reliability is shown through statistical tests of relationships among repeated test results
Validity is demonstrated through statistical tests or comparison to the gold standard
Responsiveness is measured MDC or SRM
IMPACT OF PAIN REPORTED DURING ISOMETRIC
QUADRICEPS MUSCLE STRENGTH TESTING IN PEOPLE
WITH KNEE PAIN:
DATA FROM THE OSTEOARTHRITIS INITIATIVE
DANIEL L. RIDDLE, PAUL W. STRATFORD
Min H. Huang, PT, PhD, NCS
Introduction
Common clinical assumption Impairments in body structure or function (e.g.
pain) can impact limitations in activities and participation (e.g. physical function)
Limitations of previous research NO large scale studies available Does pain affect muscle strength?
1 study: Yes
1 study: No
Relationships between Domains of the ICF Model
Purpose
Whether the relationship between maximal isometric quad strength (X1) and functional status (Y1,Y2,….Y5) was influenced by pain during isometric testing (X2)
The extent to which pain during testing (X1) affected quad strength (Y1), or other functional tests (Y2, Y3, Y4, Y5)
Purpose
Model 1 (Initial):
Physical Function (Y) = β1 Strength (X1) + covariates + ε
Model 2 (Full):
Physical Function (Y) = β1 Strength (X1) + β2 Pain (X2) + β3 Strength (X1) × Pain(X2) + covariates + ε
Y
X
Y
X
Purpose
Model 3 (No interaction)
Physical Function (Y) = β1 Strength (X1) + β2 Pain (X2) + covariates + ε
Y
X
Y
X
Model 1
Y
X
Model 2
Purpose – Class Discussion
Method
Participants (n=1,344) Unilateral knee pain
Verbal Numerical Rating (VNR) > 3
WOMAC pain >1
Outcome variables WOMAC physical
function
20-m walk
400-m walk
5 times sit to stand
Independent variables MAX Quad strength Pain during Quad
strength testing
Multiple regression models Model 1 Model 2 Model 3
95% CI of β excludes 0
Method – Class Discussion
Results
Pain did NOT modify or confound any of the outcome variables: 400-m walk, 20-m walk, chair stand, WOMAC – Physical Function.
Results
Table 6. MODERATE or SEVER pain during testing was WEAKLY associated with reduced STRENTGH, but mild pain was not.
Results – Class Discussion
Discussion
Pain during maximal isometric Quad strength tests did not affect the construct validity of the tests
Isometric Quad muscle strength and functional status relationship is NOT affected by reports of pain during testing
Discussion – Class Discussion
Limitations
Were the samples representative of the population treated?
Measurement of pain? No psychometric properties reported.
Muscle strength measured by dynamometer – Is it applicable to clinical settings using MMT?
No Hypotheses; No power estimate – finishing expedition?