Accuracy, Reliability, Validity 🎯📏

🎯 Learning Objectives

By the end of this lesson, you will be able to:
✔ Define accuracy, reliability, and validity in medical research and diagnostics
✔ Differentiate between these related but distinct concepts
✔ Interpret examples in measurement and testing
✔ Recognize their importance in epidemiology and clinical practice

1️⃣ Accuracy

✔ Definition: The degree to which a measurement reflects the true value.
👉 “How close are we to the bullseye?”

✔ Example:

• A blood pressure device that consistently gives readings close to the patient’s true blood pressure is accurate.

2️⃣ Reliability (Precision)

✔ Definition: The degree to which repeated measurements give consistent results.
👉 “How close are the arrows to each other, regardless of the bullseye?”

✔ Example:

• A thermometer that always gives the same reading when used multiple times under the same conditions is reliable, even if it’s slightly off from the true value.

3️⃣ Validity

✔ Definition: The ability of a test to measure what it is intended to measure.
👉 Combines both accuracy and reliability.

✔ Types of validity in research:

• Internal validity: Whether the study correctly measures what it set out to measure (free from bias, confounding).
• External validity (generalizability): Whether study findings can be applied to other populations.

✔ Example:

• A depression questionnaire that truly reflects clinical depression symptoms has validity.

4️⃣ Visual Analogy (Target Example 🎯)

5️⃣ Clinical & Research Relevance

• Accuracy: Lab tests must be close to the true biological value.
• Reliability: Machines and questionnaires must give consistent results.
• Validity: Studies must measure what they intend to measure.

👉 Example:

• A blood glucose meter could be reliable but inaccurate (always off by +10 mg/dL).
• A test that is accurate but unreliable would sometimes be correct but inconsistent → clinically unhelpful.

6️⃣ Quick Check: Test Your Understanding ✅

Q1: A blood pressure cuff always gives the same reading, but it’s 15 mmHg higher than actual. Which applies?
👉 Answer: Reliable but not accurate.

Q2: A depression scale measures anxiety instead of depression. Which applies?
👉 Answer: Not valid.

Q3: Which combines both accuracy + reliability?
👉 Answer: Validity.

✨ Key Takeaways

• Accuracy = closeness to truth.
• Reliability = consistency of results.
• Validity = measuring what we intend to measure (requires both accuracy + reliability).
• Critical in diagnostic testing and research design.