Contents

164 PART II: Descriptive Methodsfeelings on a vast array of topics, and often develop self-report scales for peopleto provide oral or written responses to items on the scale.Self-report scales are commonly used to measure people’s judgments aboutitems presented on the scale (e.g., divorce, political candidates, life events) orto determine differences among people on some dimension presented on thescale (e.g., personality traits, amount of stress). For example, respondents maybe asked to rate different life events according to how stressful they perceivethe events to be. The researcher then may develop a list of life events that varyon the dimension of stressfulness. This type of scale focuses on differencesamong the items on the scale, not differences among individuals. To measureindividual differences, respondents may be asked to report how often duringthe past year they experienced different stressful life events listed on a scale.A total stress score can be obtained for each individual by summing responsesto the items on the scale. Individuals can then be compared according to theamount of stress experienced during the past year. 2Self-report measures, often in the form of a questionnaire, are among themost frequently used tools in psychology. Given their importance, it is criticalthat these measures be developed carefully. Two critical characteristics of themeasurements made using self-report questionnaires are essential characteristicsof all measurements—reliability and validity.Reliability and Validity of Self-Report Measures• Reliability refers to the consistency of measurement and is frequentlyassessed using the test–retest reliability method.• Reliability is increased by including many similar items on a measure,by testing a diverse sample of individuals, and by using uniform testingprocedures.• Validity refers to the truthfulness of a measure: Does it measure what itintends to measure?• Construct validity represents the extent to which a measure assessesthe theoretical construct it is designed to assess; construct validity isdetermined by assessing convergent validity and discriminant validity.Reliable self-report measures, like reliable observers or any other reliablemeasurements, are characterized by consistency. A reliable self-report measureis one that yields similar (consistent) results each time it is administered. Selfreportmeasures must be reliable when making predictions about behavior. Forexample, in order to predict stress-related health problems, measures of individuals’life stress must be reliable. There are several ways to determine a test’sreliability. One common method is to compute a test–retest reliability. Usually,test–retest reliability involves administering the same questionnaire to a largesample of people at two different times (hence, test and retest). For a questionnaireto yield reliable measurements, people need not obtain identical scores on2The area of psychological measurement concerned with scaling items or stimuli is known aspsychophysics, and the area of measurement concerned with individual differences is referred toas psychometrics.