Chapter 5 - Chapter 5: Measuring Variables and Sampling 1....

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Chapter 5: Measuring Variables and Sampling 1. Variable: condition or characteristic that can take on different values or categories 2. Defining Measurement a. Measurement- assignment of symbols or numbers to something according to a set of rules 3. Scales of Measurement a. Nominal scale- use of symbols, such as words or numbers, to classify or categorize measurement objects into groups or types a.i. Examples: gender, marital status, personality type b. Ordinal- used to rank order objects or individuals b.i. Examples: order of finish in a race, social class, letter grade c. Interval- used to rank order, plus has equal intervals or distances between adjacent numbers c.i. Degrees Celsius, degrees Fahrenheit, IQ scores d. Ratio: fully quantitative, includes rank ordering, equal intervals, plus has an absolute zero d.i. Kelvin temperature, response time, height, weight, annual income, group size 4. Psychometric properties of good measurement a. Reliability- consistency or stability of scores b. Reliability coefficient- type of correlation coefficient used as an index of reliability b.i. 4 primary types of reliability: b.i.1. Test-retest b.i.2. Equivalent forms b.i.3. Internal consistency b.i.4. Interrater reliability c. Test-retest c.i. Consistency of a group of individuals’ scores on a test over time c.ii. Primary issue: identifying the appropriate time interval between the two testing occasions c.ii.1. The longer the time interval between the two testing occasions, the lower the reliability coefficient will be d. Equivalent- forms d.i. Consistency of a group of individuals’ scores on two versions of the same test d.ii. Examples: SAT, ACT, GRE e. Internal consistency e.i. Consistency with which items on a test measure a single construct e.ii. Affected by length of test e.iii. Goal is to obtain high reliability with relatively few items for each construct e.iv. Most commonly reported index of internal consistency: coefficient alpha e.iv.1. Also called cronbach’s alpha e.iv.2. Should be at .7 or higher
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e.iv.3. High value is evidence that the items are consistently measuring the same thing f. Interrater reliability f.i. Degree of consistency or agreement between two or more scorers, judges, observers, or raters f.ii. Measured by interobserver agreement f.ii.1. % of time that different observers’ ratings are in agreement 5. Validity a. Accuracy of inferences, interpretations, or actions made on the basis of test scores
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Chapter 5 - Chapter 5: Measuring Variables and Sampling 1....

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