Reliability in Measurement

Learning Outcomes

• Define reliability and its importance.

• Differentiate between three types of reliability:

  • Inter-Observer Reliability

  • Internal/Split-Half Reliability

  • Test-Retest Reliability

• Understand replicability of findings.

Measurement and Error

• All measurements consist of true value and measurement error:

  • $X = T + e$ (Measured Score = True Score + Error)

• Aim for: $Measured Score = True Score$

Reducing Error

• Reduce error by:

  • Increasing the number of participants (minimize individual differences).

  • Increasing the number of measurements (minimize measurement error).

  • Conducting measurements over multiple occasions.

• Averages of scores are more reliable than individual scores.

Reliability

• Reliability: consistency/repeatability of measurement results.

• Example: Consistency in measuring weight across trials.

Types of Reliability

1. Inter-Observer Reliability:

   • Agreement among observers on observations/judgements.

   • Measured using correlations between observer judgments.

2. Internal Reliability:

   • Consistency among items in a multiple-item measure.

   • High internal reliability indicates consistent measurement of constructs.

   • Assessed using Split-Half reliability (correlation between two halves of a test).

3. Test-Retest Reliability:

   • Consistency of results when a test is administered at different times.

   • Important to manage practice effects to maintain reliability.

Practice Effects

• Improvement in scores due to repeated task exposure indicates poor test-retest reliability.

Replication

• Reliability of results across different experiments.

• Necessitates detailed method sections and replication evidence.

• Importance of multiple replications to validate findings.

Summary

• Types of reliability:

  • Inter-Observer

  • Internal/Split-Half

  • Test-Retest

• Distinction between reliability and replication is crucial for scientific integrity.