CHAPTER 5 MEASUREMENT CONCEPTS © 2007 The McGraw-Hill Companies, Inc.

LEARNING OBJECTIVES Describe the problem of reactivity of a measure of behavior and discuss ways to minimize reactivity Describe the properties of the four scales of measurement: nominal, ordinal, interval, and ratio © 2012 The McGraw-Hill Companies, Inc.

LEARNING OBJECTIVES Define reliability of a measure of behavior and describe the difference between test-retest, internal consistency, and interrater reliability Discuss ways to establish construct validity, including predictive validity, concurrent validity, convergent validity, and discriminant validity © 2012 The McGraw-Hill Companies, Inc.

RELIABILITY OF MEASURES Consistency or Stability of a Measure of Behavior True Score Measurement Error Pearson Product-Moment Correlation Coefficient © 2012 The McGraw-Hill Companies, Inc.

If the scale is always off by 10 pounds, does it have reliability and/or validity? © 2012 The McGraw-Hill Companies, Inc.

Pearson’s product moment correlation coefficient (r) - 1.00 + 1.00 0.00 Variables covary in opposite directions Variables covary in the same direction © 2012 The McGraw-Hill Companies, Inc.

Measurement Concepts Chp 5 Reliability refers to the consistency, precision or stability of a measure of behavior pg96 Are the results the same or very similar each time you measure a variable? Measures that change or fluctuate are not reliable (assuming change is not due to the variable changing) Any measure has two parts 1) true score- real value of the variable and 2) measurement error-is shown by the greater variability Reliability is increased when we increase the number of items in our measure, survey or test (pg97)

How reliable are personality quizzes in magazines? © 2012 The McGraw-Hill Companies, Inc.

Measuring Reliability We can measure reliability using the Pearson product moment correlation coefficient pg98 To calculate reliability we must have at least two scores on the measure across individuals. If the measure is reliable the two scores should be similar for each of the individuals studied (high positive correlation For most measures coefficient should be at least .80) pg 98 Types of Reliability 1) Test-Retest –Measures the same individuals at least for two points in time then calculate the Pearson product moment r between the scores. Test-Retest reliability is sometimes called a coefficient of stability in that it measures how stable is the trait being measured (Discuss some threats to validity for this measure) This is not a good measurement for traits that are considered to be in a state of flux or events occurring between the two administrations of the test

Measuring Reliability 2) Equivalent Form-Can avoid problems associated with Test-Retest by giving equivalent forms of the same test to the same set of people, calculating the correlation between the two scores. You can administer the two tests close in time (something you cannot do with Test-Retest). However to the extent that the two forms are not totally equivalent a new source of error is introduced. Equivalent forms usually yield lower estimates of reliability

Measuring Reliability Split-Half Reliability-Test is administered once, then the test is split in half, scored separately and a Pearson r is calculated for each score Split-Half-correlation between the first and second half of the measurement Odd-Even correlation between the even items & odd items of a measurement In either case only one administration is required and the coefficient is determined by the internal components of the test (aka internal consistency reliability) Split-half not meaningful in speed tests (in which most items are not difficult and score depends on how many items answered correctly e.g. algebra test) Coefficient of reliability is inflated* Item-Total correlations-Look at the correlation between each item score with the total score, based on all items (also measures internal consistency) Cronbach’s alpha -is a coefficient of internal consistency Cronbach's alpha generally increases when the correlations between the items increase. For this reason the coefficient is also called the internal consistency or the internal consistency reliability of the test pg99-100

Interrater Reliability In research in which raters observe behaviors and make ratings or judgments (and then those judgments are compared and agree determines interrater reliability) Bandura (1961) conducted a study to investigate if social behaviors (i.e. aggression) can be acquired by imitation 36 boys and 36 girls were tested from the Stanford University Nursery School aged between 3 to 6 years old. The role models were one male adult and one female adult Under controlled conditions, Bandura arranged for 24 boys and girls to watch a male or female model behaving aggressively towards a toy called a 'Bobo doll'. The adults attacked the Bobo doll in a distinctive manner - they used a hammer in some cases, and in others threw the doll in the air and shouted "Pow, Boom“. Another 24 children were exposed to a non-aggressive model and the final 24 child were used as a control group and not exposed to any model at all. To test the inter-rater reliability of the observers, 51 of the children were rated by two observers independently and their ratings compared. These ratings showed a very high reliability correlation (r = 0.89), which suggested that the observers had good agreement about the behavior of the children https://www.youtube.com/watch?v=hHHdovKHDNU

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 © 2012 The McGraw-Hill Companies, Inc.

CONSTRUCT VALIDITY OF MEASURES Indicators of Construct Validity Face validity Content validity Predictive validity Concurrent validity Convergent validity Discriminant validity © 2012 The McGraw-Hill Companies, Inc.

Construct Validity Face Validity The content of the measure appears to reflect the construct being measured Content validity The content of the measure is linked to the universe of content that defines the construct Predictive validity Scores on the measure predict behavior on a criterion measured at a time in the future Concurrent validity Scores on the measure are related to a criterion measured at the same time (concurrently) Convergent validity Scores on the measure are related to other measures of the same construct Discriminant validity Scores on the measure are not related to other measures that are theoretically different © 2012 The McGraw-Hill Companies, Inc.

RESEARCH ON PERSONALITY AND INDIVIDUAL DIFFERENCES Systematic and detailed research on validity is most often carried out on measures of personality and individual differences Should use measures of personality that have demonstrable validity and reliability Example: Mental Measurement Yearbook © 2012 The McGraw-Hill Companies, Inc.

REACTIVITY OF MEASURES Measure is reactive if awareness of being measured changes an individual’s behavior Measures of behavior vary in terms of their potential reactivity © 2012 The McGraw-Hill Companies, Inc.

VARIABLES AND MEASUREMENT SCALES Nominal Scales Ordinal Scales Interval and Ratio Scales The Importance of the Measurement Scales © 2012 The McGraw-Hill Companies, Inc.

Scales of measurement Scale Description Example Distinction Nominal Categories with no numeric scales Males / females Introverts / extroverts Impossible to define any quantitative values Ordinal Rank ordering numeric values limited 2-, 3-, and 4-star restaurants Ranking TV programs by popularity Intervals between items is unknown Interval Numeric properties are literal Assume equal intervals between values Intelligence Aptitude test scores Temperature (Fahrenheit and Celsius) No true zero point Ratio Zero indicates absence of variable measured Reaction time Weight Age Frequency of behavior Can form ratios (someone weighs twice as much as another) © 2012 The McGraw-Hill Companies, Inc.