Test Accuracy in Clinical Practice

Overview

This lecture explains the concepts of sensitivity and specificity in clinical testing, their importance for test accuracy, and how to apply them in physiotherapy practice.

Test Validity and Accuracy

• Validity is the degree to which a test measures what it claims, e.g., a scale measuring weight.
• Accuracy in clinical testing helps determine which test to use for confirming or excluding a diagnosis.

True/False Positives and Negatives

• True Positive (TP): Sick people correctly identified as sick.
• True Negative (TN): Healthy people correctly identified as healthy.
• False Positive (FP): Healthy people incorrectly identified as sick.
• False Negative (FN): Sick people incorrectly identified as healthy.
• No test is 100% accurate in real life.

Sensitivity

• Sensitivity measures a test’s ability to correctly identify those with the disease (true positives).
• A 100% sensitive test has no false negatives.
• High sensitivity is important when missing a disease could be fatal.
• SNOUT mnemonic: Highly SeNsitive test, Negative result rules OUT the disease.

Specificity

• Specificity measures a test’s ability to correctly identify those without the disease (true negatives).
• A 100% specific test has no false positives.
• High specificity is important for confirmation of a diagnosis.
• SPIN mnemonic: Highly SPecific test, Positive result rules IN the disease.
• Trade-off: Highly specific tests may miss some true cases (false negatives).

Example: Radicular Pain Testing

• Straight Leg Raise (SLR) test: Sensitivity 92%, Specificity 28%.
• Cross SLR test: Sensitivity 28%, Specificity 90%.
• Use SLR to rule out (exclude) the disease (SNOUT).
• Use cross SLR to confirm (include) the diagnosis (SPIN).

Key Terms & Definitions

• Validity — the extent to which a test measures what it is supposed to measure.
• True Positive (TP) — sick person correctly identified as sick.
• True Negative (TN) — healthy person correctly identified as healthy.
• False Positive (FP) — healthy person incorrectly identified as sick.
• False Negative (FN) — sick person incorrectly identified as healthy.
• Sensitivity (SN) — ability of a test to identify all sick individuals correctly.
• Specificity (SP) — ability of a test to identify all healthy individuals correctly.

Action Items / Next Steps

• Learn how to calculate sensitivity and specificity values.
• Review further materials or watch calculation tutorial (video recommended).
• Practice applying SNOUT and SPIN mnemonics to real clinical scenarios.