Transcript Document

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!
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 116.5 and 123.5 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 Test
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
Relevant clinical
population
Perform the reference standard
– on everyone
Perform the clinical test
– 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 designrelated 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
Reference Standard Positive
True Positive
Result
Diagnostic Test
Positive
Diagnostic Test
Negative
Reference Standard Negative
False Positive
Result
A
B
False Negative
Result
True Negative
Result
A+B
C+D
C
A+C
D
B+D
N
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 False Positive
Result
Result
A
B
False
Negative
Result
True Negative
Result
C
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
False Positive
Result
A
B
False Negative True Negative
Result
Result
C
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
-LR
Interpretation
> 10
< .1
Large and conclusive
shifts in probability
5-10
.1-.2
Moderate shifts in
probability
2-5
.2-.5
Small shifts in probability
1-2
.5-1
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
So is this a good test for screening
for Achilles Tendon rupture?
• Link to video
• So if this test is negative, does the patient have a
rupture? Not Likely!
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.
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
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
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: 0.91
+ LR = 6.0
- 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 Summary
• Clinical Practice Guideline at JOSPT
Questions?
• Please visit the PTNow website
• Give us feedback
• How can we help you?