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Psych 818 Psychological Measurement

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DeShon - Introduction. Psych 818 Psychological Measurement. Preliminaries. Who am I? Your job - Ask questions and find a way to become intellectually engaged Self-handicapping is unproductive You have a huge role in the success of the class All work is your own! Syllabus and Grading. - PowerPoint PPT Presentation

Text of Psych 818 Psychological Measurement

  • Psych 818Psychological MeasurementDeShon - Introduction

  • PreliminariesWho am I?

    Your job - Ask questions and find a way to become intellectually engagedSelf-handicapping is unproductiveYou have a huge role in the success of the class

    All work is your own!

    Syllabus and Grading

  • PurposeMeasurement TheoryMeasure DevelopmentMeasure UseMeasure Interpretation

    Exposure to Measurement thinkingExposure to Measurement papersExposure to Measurement Standards

  • Responsibility!As a Psychologist YOU will likely have substantial effects on the course of many lives through the use of tests and measuresClinical DiagnosisPolicy Making & Risk FactorsEducational OpportunitiesWork OpportunitiesExample: Police promotion & expert witnessYou will have the power to help or hurt many people (and their families!)

  • Measurement & PolicyMeasurement often starts as an academic investigationThen, over time, transfers to policy and decision makingExamples:The Kilogram conundrumMPG vs GPM

  • Standards for MeasurementAPA standards for educational and psychological testing and assessmentThis is your professional bible.You will be held professionally accountable to these standardsTherefore, you better know them!

  • Beginning QuestionsWhy do we measure?

    What is measurement?

  • Why do we measure?Decision making



  • What is Measurement?S.S. Stevens The assignment of numerals to objects or events according to a rule.Warren Torgerson The assignment of numbers to perceived attributes of objects or events according to a rule.Lyle Jones Measurement is the determination of the magnitude of a specified attribute of an object or event in terms of a unit of measurement.Classification (including ordering) is not measurement.

  • What is Measurement?Cliffs definitionGood measurement is the assignment of numbers to perceived attributes of objects or events according to rules that are easily understood; are easily used; yield numbers that are as simply related as possible to as many other sets of measurements as possible.

  • Measurement QuestionsFundamental measurement questionsWhat is our best estimate of a psychologically relevant quantityValidity

    How precise is our estimate or...How much error is there in our estimateReliability

  • Analogy with statisticsMeasurement questions look a lot like statistical questionsWhat's our best estimate of a population meanHow precise is our estimate (e.g., standard errors and confidence intervals)

  • History of MeasurementMost early measurements occurred in physics, chemistry, and much later in biology (e.g., bacteria)Much attention paid to measuring specific quantities such as temperature, pressure, pH, etc...But no serious attention given to a general theory of measurementAlso, little attention paid to a general model of reliability and validity

  • Two Physical Measurement Examples TemperatureFundamental to virtually all future discoveries in physics

    PHFundamental to the understanding of the basic elements (i.e., hydrogen) and chemistry

  • TemperatureIn the beginning there was the PERCEPTION of hot and coldAristotles fundamental qualitiesHot and cold were conceived of as opposing qualities of objectVirtually all measurements are rooted in subjective perceptionPerceptions are fallible!

    200BC Philos air thermoscope

  • Temperature (cont.)1592 Galileo reinvents Philos (200BC) air thermoscope (instrument or indicator)This is an indicator with no scaleNot a measurement?Very sensitive to temperature changes

    But also open to the air so sensitive to other variables (e.g., Air Pressure)validity problem

  • Problems with Air ThermoscopesNo scale so a qualitative instrumentConstruct contamination - Validityopen to the air so sensitive to other variables (e.g., Air Pressure)What liquid to use? (water, spirits, quicksilver)State changes, sensitivity and linearity of expansion ratesNo standardized construction so other instruments are not equivalent Inaccurate conceptualization of heat

  • Fix the validity problemsSeal the thermoscopeDuke Ferdinand II (1632)Pascal (1663) proved that air pressure caused errors in open air thermometersAre measurement errors reliability or validity

    Use quicksilver (i.e., mercury)Fareinheit

  • Fix the scaling problemsMany individuals developed scales to assign numbers to the level of liquid in the thermometer (now a thermo meter)!Newton (1700)"zeroth degree of heat" as melting snow and "33 degrees of heat" as boiling waterRmer (1708)Raumur (1731)freezing point of water is 0 degrees, the boiling point 80 degrees Fareinheit (1724)0 as the melting point of an equal mixture of ice and salt and 96 as blood heatDelisle (1732)2400 graduations: 0 degrees as the boiling point and 150 degrees as the freezing point of water. Celcius (1742)freezing point of water at 0 C and the boiling point at 100 C

  • Proliferation of Scales

  • UnitsThese scales result in degrees or units

    What are some psychological units?

    Check out these physical units!

  • Comparison of temp. scales

  • Transformations to Equate scales

  • Fix the standardization or calibration problemsThe technology of glass blowing made it very difficult to construct exactly equal instruments (the size of the liquid resivoir, the amount of liquid, the bore of the tube, etcall must be identical to yield identical readings.Instead, calibrate or equate using fixed reference pointsRoyal Society thermometers

  • Theoretical UnderstandingThe various scales of measurement and the calibration of thermometers to fixed points allowed systematic investigationsThat resulted in improved understanding of what thermometers measure (heat)

    Kelvins scale of temperature (1848)Rational scale with absolute zeroBased on gas laws and carnot cyclesAdopted in 1954!

  • Example 2: pH - Acids & BasesIn the beginning there was perceptionGreeks attempted to characterize natureOne fundamental character of nature was taste.SaltySour the greek word for sour is the base of our word for acidBitterSweet

  • Acids and BasesNext, it turned out that sour tasting substances had other regular propertieschanges the color of litmus (a dye extracted from a lichen commonly known as dyer's weed.) Corrodes metals

    No real understanding of acids

  • AcidsHuge proliferation of acid types (named by the method used to form the acid)Muratic acid, acetic acid, sulphuric acid, hydrofluoric acid, phosphoric acid, pyruvic acid

    No clear picture of the cause for the common functioning of acidsLavoisier (1776) thought it was oxygen that caused substances to be acidicGreek word oxein meaning 'sour' and gennan meaning 'to generate

  • AcidsLeibig (1850s) noticed that all acids have hydrogen in commonThis insight required knowledge of the elements, molecules, and weights of molecules (another measurement problem)

    Sorenson (1909) developed the scale for indexing the activity of hydrogen in a substance

  • AcidspH = (power of hydrogen ) is a measure of the activity of hydrogen ions (H+) in a solutionLog of number of H+ molecules in a substance pH value has no unit but it is not an arbitrary scaleThe number arises from a definition based on the activity of hydrogen ions in the solution has an absolute zero

  • Measurement of pHMany ways now exist to measure pH.Early measurements were based on the color of a substance resulting from a chemical reactionpH indicatorA pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined easily. Hence a pH indicator is a chemical detector for protons (H+). Normally, the indicator causes the color of the solution to change depending on the pH. -Wilkpedia

  • pH Measurement

  • pH MeasurementAdding the indicator does not result in an absolute shift from one color to the other.Instead, it is a gradual shift and the resulting color must be compared to a SCALE to determine the pH.

  • Scaling pH Indicators

  • pH and IRT similaritiesThe colormetric approach to pH has a great deal of overlap with current Item Response approaches to measurement IRT

    Keep this in mind when we get to IRT

  • Causality and MeasurementMeasurement requires causal inferenceChanges in the level of the latent entity cause changes in the level of the indicator variable(s).

    This inference requires the same scientific method as any causal research question.Must show that the latent variable is the only cause of the indicator (construct validity)

  • ConstructsWhat is a construct?Constructs become better defined via researchTemperature, pH, bacteria, gas pressure, electricity1. An unobserved cause of variation in an observable variable(s)2. A label used to describe a pattern of observed covariances

  • Model of MeasurementConstructConstruct = an unobservable but real causal variable(aka latent variable)Indicator / InstrumentIndicator = an observable variable thatis solely caused by the construct andsensitive to changes in the level of the constructScale: the rule for assigning numbers to the levels of theindicator or instrument

  • Basic Measurement ModelConstructMeasure 1Measure 2Measure 3Error 1Error 2Error 3

  • Some quotes to think about"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind: it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science, whatever the matter may be. - Sir William Thomson, Lord Kelvin. 1889

    Whatever exists at all, exists in some amount. To know it thoroughly involves knowing its quality as well as its quantity - Thorndike, 1918