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Measurement Concepts

Review from Wed… 3 Main Types of Validity: Construct Validity – are you measuring what you think you’re measuring Internal Validity – how certain are you that the IV effected the DV External Validity – can your results be replicated by others in another setting

Review of Validity Lab experiments (using the experimental method) are typically high in internal validity because…? Lab experiments are usually high in ____ validity but low in _____ validity.

RELIABILITY OF MEASURES Reliability = consistency or stability of a measure True Score Measurement Error Pearson Product-Moment Correlation Coefficient

Less error

RELIABILITY OF MEASURES Reliability of your measure is important You only get one shot Leads to stability and replication

Pearson r Variables covary in opposite directions Variables covary in the same direction r =.675

RELIABILITY OF MEASURES Test-Retest Reliability Assessed by measuring the same individuals two points in time Vulnerable to artificiality Vulnerable to maturation

RELIABILITY OF MEASURES Internal Consistency Reliability = because all items measure the same thing, they should be similar and consistent Split-half reliability Cronbach’s alpha Item-total correlations Interrater Reliability Correlation between the observations of raters

RELIABILITY OF MEASURES Reliability and Accuracy of Measures Reliability indexes do not indicate whether a particular measure is an accurate measure of the variable of interest A measure can be highly reliable but not accurate