Measurement and Operational Definitions

Operational Definitions and Measurement

• Operational definitions are important for designing accurate measurement scales.
• More precise conceptual definitions lead to more effective measurement scales.

Common Types of Measures

• There are three main types of measures: self-report, observational, and physiological.
• Self-report measures involve asking people direct questions about themselves.
• Observational measures involve recording behaviors.
• Physiological measures utilize equipment to measure biological processes.

Measurement Techniques

• Researchers can create their own measurement scales or use existing ones.
• New measures should be tested against existing ones to ensure validity.

Levels of Measurement

• There are nominal and quantitative levels of measurement.
• Categorical (nominal) variables classify items into categories like gender, race, or species.
• Quantitative variables involve meaningful numerical representations.

Quantitative Variables

• Quantitative variables can be ordinal, interval, or ratio scales.
• Ordinal scales rank items but don't provide precise measurements between ranks.
• Interval scales include precise measurements between values but lack a true zero point.
• Ratio scales offer a true zero point, allowing for comparisons of magnitudes like "twice as much".

Likert Scale

• The Likert scale, a common psychological measure, is an interval scale using a "rate on a scale of 1 to x" format.
• Typically uses a 1 to 5, 1 to 7, or 1 to 9 scale.
• Odd numbers ensure a neutral middle point.
• Scale choices must be consistent across all questions.

Reliability

• Reliability refers to a measure's ability to consistently provide the same results.
• It is an essential component of construct validity.

Types of Reliability

• Test-retest reliability measures consistency when the same test is administered twice.
• Interrater reliability assesses agreement between independent observers.
• Internal reliability ensures all items on a scale measure the same concept.

Testing Reliability

• Reliability can be assessed using various techniques, including scatterplots and correlation coefficients.
• The correlation coefficient, denoted by 'r', ranges between -1 and 1.
• Test-retest reliability is easily measured with 'r'.
• Quantitative variables use 'r' to measure interrater reliability.
• Qualitative variables utilize a statistic called kappa to assess interrater reliability (kappa should be at least 0.70).

Testing Internal Reliability

• Internal reliability, usually measured using Cronbach's alpha, is crucial for self-report scales.
• Cronbach's alpha examines the correlations between different items on a scale (should be at least 0.70).

Measurement Validity

• Measurement validity relates to the measure's ability to accurately reflect the intended concept in the real world.
• Unlike reliability, it lacks easy statistical measures.

Types of Measurement Validity

• Face validity refers to the measure's apparent plausibility.
• Construct validity evaluates the measure's ability to capture the entire concept.
• Predictive validity assesses whether the measure predicts future observed results.
• Concurrent validity checks whether the measure aligns with current observed results.