Role of Tests and Measures in Clinical Practice Paul Mintken PT, DPT, OCS, FAAOMPT Associate Editor, Tests & Measures, PTNow Associate Professor Physical Therapy Program University of Colorado School of Medicine

Objectives Understand what makes a good test/measure Explain the basic constructs of reliability and validity Describe the principles of sensitivity, specificity, and likelihood ratios. Understand the value of comparing a test/measure to some reference or gold standard Access the PTNow website for further information!

Why Do I Choose a Measure in My Clinical Practice? To help me, as a clinician, see the effect of my treatment. –Am I getting the results I should? –Am I clinically effective? How do I compare with what’s been published? –I want to monitor and review progress in an objective manner. –I want to use a measure to help motivate my patient.

What Makes a Good Test/Measure? A test must be reliable within and between testers, and give the same result at different times Each time a test/measure is performed we must understand how the results of the test compare with the truth. This is determined by comparing the test results with a measure of the truth. So—how do we do this?

Standard Error of Measurement Describes the range (+/-) within which a patient’s true score might fit within a given test. Example: –SEM for knee flexion goniometry is 3.5 degrees –Measured range is 120 degrees –The variation of the true/actual ROM would be between and degrees

Differences Minimal Clinically Important Difference (MCID) –The smallest change in scores that patients perceive as important –Similar to the concept of CLINICAL SIGNIFICANCE Minimal Detectable Change (MDC) –Commonly expressed as MDC90 or MDC95 –An index of the reliability of an outcome measure –Similar to the concept of STATISTICAL SIGNIFICANCE MDC90: Minimum change at 90% confidence –The amount of change in scores required to be 90% confident that it is beyond measurement error

Responsiveness Does the outcome detect changes over time that matter to the patient? Ability of outcome to detect small, but clinically important differences Ceiling & Floor Effects –Ceiling: When the task is too easy, and all patients perform at or near perfect, you have a ceiling effect. –Floor: When the task is too hard and everyone performs at the worst possible level.

EXAMPLE: Achilles Tendinopathy Your patient is a 26-year-old male who was running and heard/felt a “pop” in his left Achilles tendon 3 days ago. He has been able to walk on it with a pronounced limp. There is substantial swelling and discoloration in the posterior heel.

Clinical Summaries Achilles Tendinitis/Tendinopathy

What is the “likelihood” this patient ruptured the Achilles tendon? Let’s go to PTNow: Clinical tools Search by practice area Search by body part Search by ICF domain –Thompson TestThompson Test

In a retrospective study of 174 patients over 13 years with unilateral tears in which surgery was the reference or “gold” standard –Sensitivity: 0.96 –Specificity: 0.98 –+LR=48.00 –-LR=0.04 Link to video

Relevant clinical population Perform the clinical test – on everyone Perform the reference standard – on everyone Compare the results “The optimal design for assessing the accuracy of a diagnostic test is considered to be a prospective blind comparison of the test and the reference in a consecutive series of patients from a relevant clinical population.” Lijmer JG, Mol BW, Heisterkamp S, et al. Empirical evidence of design- related bias in studies of diagnostic tests. JAMA. 1999;282(11):1062.

SnNouts and SpPins  Mnemonics to remember the most useful aspects of tests with moderate to high sensitivity and specificity SnNout : A test with a high sensitivity value (Sn) that, when negative (N), helps to rule out a disease (out) SpPin : A test with a high specificity value (Sp) that, when positive (P) helps to rule in a disease (in)

Contingency Table True Positive Result A False Positive Result B False Negative Result C True Negative Result D Diagnostic Test Positive Diagnostic Test Negative Reference Standard PositiveReference Standard Negative A + B C + D N A + C B + D

Definition: Sensitivity Sensitivity –Test’s ability to obtain a positive test when the target condition is really present –Based on the True Positives – Calculated as: A/(A + C) True Positive Result A False Positive Result B False Negative Result C True Negative Result D

Definition: Specificity Specificity –Test’s ability to obtain a negative test when the target condition is really absent –Based on the True Negatives –Calculated as: D/(B + D) True Positive Result A False Positive Result B False Negative Result C True Negative Result D

What are likelihood ratios? Positive likelihood ratio (LR+) –reflects the odds that a person who tests positive actually DOES have the disorder Negative likelihood ratio (LR–) –reflects the odds that a person who tests negative actually DOES NOT have the disorder

+LR-LRInterpretation > 10 <.1 Large and conclusive shifts in probability Moderate shifts in probability Small shifts in probability Rarely alters probability to an important degree

Thompson Test In a retrospective study of 174 patients over 13 years with unilateral tears in which surgery was the reference or “gold” standard –Sensitivity: 0.96 –Specificity: 0.98 –+LR=48.00 –-LR=0.04 Link to video So if this test is negative, does the patient have a rupture? Not Likely! So is this a good test for screening for Achilles Tendon rupture?

Next Question: Does this patient have Achilles tendinopathy? Let’s go to PTNow: Clinical summary Achilles tendinopathy Search clinical tools –Achilles Tendon Palpation –Arc Sign –Royal London Test Maffulli N, Kenward MG, Testa V, Capasso G, Regine R, King JB. Clinical diagnosis of Achilles tendinopathy with tendinosis. Clin J Sport Med. 2003;13:11-15.

Achilles Tendon Palpation Achilles Tendon Palpation Most Sensitive Test Description: Gentle palpation of the Achilles tendon is performed by squeezing the tendon between thumb and index fingers. The patient indicates whether pain was present or absent. Sensitivity: 0.58 –(Not great!) Specificity: 0.84 Intratester reliability –0.27 to 0.72 Intertester reliability –0.72 to 0.85

Royal London Test Royal London Test Most Specific Test Examiner identifies portion of Achilles tendon that is maximally tender to palpation The patient then actively dorsiflexes ankle Examiner once again palpates part of tendon that was identified as maximally tender in maximal dorsiflexion Patients with Achilles tendinopathy report a substantial decrease or absence of pain when palpated in dorsiflexion Sensitivity: 0.54 Specificity: LR = LR = 0.51 Intratester reliability –0.60 to 0.89 Intertester reliability –0.63 to 0.76

Evidence to Practice Nomogram –Pretest probability = 20% of runners develop Achilles problems –+LR = 6 –Posttest probability ~65% Is a treatment threshold reached? –The point at which the examination and evaluation process stops and treatment begins

Patient diagnosed with Achilles tendinopathy What treatments are recommended? Go to the Clinical SummaryClinical Summary Clinical Practice Guideline at JOSPTClinical Practice Guideline

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