2 MeasurementThe assignment of numbers to represent the amount of an attribute present in an object or person, using specific rulesAdvantages:Removes guessworkProvides precise informationLess vague than words
3 Levels of MeasurementThere are four levels (classes) of measurement:Nominal (assigning numbers to classify characteristics into categories) Gender, religionOrdinal (ranking objects based on their relative standing on an attribute) "very dissatisfied," "somewhat dissatisfied," "somewhat satisfied," or "very satisfied."Interval (objects ordered on a scale that has equal distances between points on the scale) Fahrenheit scale of temperatureRatio (equal distances between score units; there is a rational, meaningful zero) amount of money you have in your pocket right nowA variable’s level of measurement determines what mathematic operations can be performed in a statistical analysis.
4 Errors of Measurement Obtained Score = True score ± Error Obtained score: An actual data value for a participant (e.g., anxiety scale score)True score: The score that would be obtained with an infallible measureError: The error of measurement, caused by factors that distort measurement
5 Factors That Contribute to Errors of Measurement Situational contaminantsTransitory personal factors (e.g., fatigue)Response-set biasesAdministration variationsItem sampling
6 Question Is the following statement True or False? The true score is data obtained from the actual research study.
7 AnswerFalseThe true score is the score that would be obtained with an infallible measure. The obtained score is an actual value (datum) for a participant.
8 Psychometric Assessments A psychometric assessment is an evaluation of the quality of a measuring instrument.Key criteria in a psychometric assessment:ReliabilityValidity
9 ReliabilityThe consistency and accuracy with which an instrument measures the target attributeReliability assessments involve computing a reliability coefficient.Reliability coefficients can range from .00 to 1.00.Coefficients below .70 are considered unsatisfactory.Coefficients of .80 or higher are desirable.
10 Three Aspects of Reliability Can Be Evaluated StabilityInternal consistencyEquivalence
11 StabilityThe extent to which scores are similar on two separate administrations of an instrumentEvaluated by test–retest reliabilityRequires participants to complete the same instrument on two occasionsAppropriate for relatively enduring attributes (e.g., creativity)
12 Internal ConsistencyThe extent to which all the items on an instrument are measuring the same unitary attributeEvaluated by administering instrument on one occasionAppropriate for most multi-item instrumentsThe most widely used approach to assessing reliabilityAssessed by computing coefficient alpha (Cronbach’s alpha)Alphas ≥.80 are highly desirable.
13 QuestionWhen determining the reliability of a measurement tool, which value would indicate that the tool is most reliable?0.500.700.901.10
14 Answerc. 0.90Reliability coefficients can range from 0.0 to Coefficients of 0.80 or higher are desirable. Thus, a coefficient of 0.90 would indicate that the tool is very reliable. A value greater than 1.00 for a coefficient would be an error.
15 EquivalenceThe degree of similarity between alternative forms of an instrument or between multiple raters/observers using an instrumentMost relevant for structured observationsAssessed by comparing agreement between observations or ratings of two or more observers (interobserver/interrater reliability)
16 Reliability Principles Low reliability can undermine adequate testing of hypotheses.Reliability estimates vary depending on procedure used to obtain them.Reliability is lower in homogeneous than heterogeneous samples.Reliability is lower in shorter than longer multi-item scales.
17 ValidityThe degree to which an instrument measures what it is supposed to measureFour aspects of validity:Face validityContent validityCriterion-related validityConstruct validity
18 Face ValidityRefers to whether the instrument looks as though it is an appropriate measure of the constructBased on judgment; no objective criteria for assessment
19 Content ValidityThe degree to which an instrument has an adequate sample of items for the construct being measuredEvaluated by expert evaluation, often via a quantitative measure—the content validity index (CVI)
20 Question Is the following statement True or False? Face validity of an instrument is based on judgment.
21 AnswerTrueFace validity refers to whether the instrument looks like it is an appropriate measure of the construct. There are no objective criteria for assessment; it is based on judgment.
22 Criterion-Related Validity The degree to which the instrument is related to an external criterionValidity coefficient is calculated by analyzing the relationship between scores on the instrument and the criterion.Two types:Predictive validity: the instrument’s ability to distinguish people whose performance differs on a future criterionConcurrent validity: the instrument’s ability to distinguish individuals who differ on a present criterion
23 Construct Validity Concerned with these questions: What is this instrument really measuring?Does it adequately measure the construct of interest?
24 Some Methods of Assessing Construct Validity Known-groups techniqueTesting relationships based on theoretical predictionsFactor analysis
25 Criteria for Assessing Screening/Diagnostic Instruments Sensitivity: the instruments’ ability to correctly identify a “case”—i.e., to diagnose a conditionSpecificity: the instrument’s ability to correctly identify noncases, that is, to screen out those without the conditionLikelihood ratio: Summarizes the relationship between sensitivity and specificity in a single numberLR+: the ratio of true positives to false positivesLR-: the ratio of false negatives to true negatives