psych 818 psychometric theory and measure construction deshon - 2007
DESCRIPTION
Purpose Measure Use Measure Use Measure Interpretation Measure Interpretation Measure Development Measure Development Exposure to Measurement thinking Exposure to Measurement thinking Exposure to Measurement papers Exposure to Measurement papers Exposure to Measurement Standards Exposure to Measurement StandardsTRANSCRIPT
Psych 818Psych 818Psychometric Theory and Psychometric Theory and
Measure ConstructionMeasure ConstructionDeShon - 2007DeShon - 2007
PreliminariesPreliminaries Who am I?Who am I?
Your job - Ask questions and find a way to Your job - Ask questions and find a way to become intellectually engagedbecome intellectually engaged Self-handicapping is unproductiveSelf-handicapping is unproductive You have a huge role in the success of the classYou have a huge role in the success of the class
All work is your own!All work is your own!
Syllabus and GradingSyllabus and Grading
PurposePurpose Measure UseMeasure Use Measure InterpretationMeasure Interpretation Measure DevelopmentMeasure Development
Exposure to Measurement thinkingExposure to Measurement thinking Exposure to Measurement papersExposure to Measurement papers Exposure to Measurement StandardsExposure to Measurement Standards
Responsibility!Responsibility! As a Psychologist As a Psychologist YOUYOU will likely have will likely have
substantial effects on the course of many substantial effects on the course of many lives through the use of tests and lives through the use of tests and measuresmeasures Clinical DiagnosisClinical Diagnosis Policy Making & Risk FactorsPolicy Making & Risk Factors Educational OpportunitiesEducational Opportunities Work OpportunitiesWork Opportunities
Example: Police promotion & expert witnessExample: Police promotion & expert witness You will have the power to help or hurt You will have the power to help or hurt
many people (and their families!)many people (and their families!)
Standards for MeasurementStandards for Measurement APA standards for educational and APA standards for educational and
psychological testing and psychological testing and assessmentassessment This is your professional bible.This is your professional bible. You will be held professionally You will be held professionally
accountable to these standardsaccountable to these standards Therefore, you better know them! ;)Therefore, you better know them! ;)
Your responsibility and fair game for test Your responsibility and fair game for test questionsquestions
Beginning QuestionsBeginning Questions Why do we measure?Why do we measure?
What is measurement?What is measurement?
Why do we measure?Why do we measure? Decision makingDecision making
PredictionPrediction
ResearchResearch
What is Measurement?What is Measurement? S.S. StevensS.S. Stevens
The assignment of numerals to objects or events The assignment of numerals to objects or events according to a rule.according to a rule.
Warren TorgersonWarren Torgerson The assignment of numbers to The assignment of numbers to perceived perceived
attributesattributes of objects or events according to a of objects or events according to a rule.rule.
Lyle JonesLyle Jones Measurement is the determination of the Measurement is the determination of the
magnitude of a specified attribute of an object or magnitude of a specified attribute of an object or event in terms of a unit of measurement.event in terms of a unit of measurement.
Classification (including ordering) is not Classification (including ordering) is not measurement.measurement.
What is Measurement?What is Measurement? Cliff’s definitionCliff’s definition GoodGood measurement is the measurement is the
assignment of numbers to perceived assignment of numbers to perceived attributes of objects or events attributes of objects or events according to rules that according to rules that are easily understood; are easily understood; are easily used; are easily used; yield numbers that are as simply related yield numbers that are as simply related
as possible to as many other sets of as possible to as many other sets of measurements as possible. measurements as possible.
History of MeasurementHistory of Measurement Most early measurements occurred in Most early measurements occurred in
physics, chemistry, and much later in physics, chemistry, and much later in biology (e.g., bacteria)biology (e.g., bacteria)
Much attention paid to measuring Much attention paid to measuring specific quantities such as specific quantities such as temperature, pressure, pH, etc...temperature, pressure, pH, etc... But no serious attention given to a But no serious attention given to a
general theory of measurementgeneral theory of measurement Also, little attention paid to a general Also, little attention paid to a general
model of reliability and validitymodel of reliability and validity
Two Physical Measurement Two Physical Measurement Examples Examples
TemperatureTemperature Fundamental to virtually all future Fundamental to virtually all future
discoveries in physicsdiscoveries in physics
PHPH Fundamental to the understanding of the Fundamental to the understanding of the
basic elements (i.e., hydrogen) and basic elements (i.e., hydrogen) and chemistrychemistry
TemperatureTemperature In the beginning there was the PERCEPTION of In the beginning there was the PERCEPTION of
hot and coldhot and cold Aristotle’s fundamental qualitiesAristotle’s fundamental qualities Hot and cold were conceived of as opposing qualities Hot and cold were conceived of as opposing qualities
of objectof object Virtually all measurements are rooted in subjective Virtually all measurements are rooted in subjective
perceptionperception Perceptions are fallible!Perceptions are fallible!
200BC Philo’s air thermoscope200BC Philo’s air thermoscope
Temperature (cont.)Temperature (cont.) 1592 Galileo reinvents 1592 Galileo reinvents
Philo’s (200BC) air Philo’s (200BC) air thermoscope (instrument thermoscope (instrument or indicator)or indicator) This is an indicator with no This is an indicator with no
scalescale Not a measurement?Not a measurement?
Very sensitive to Very sensitive to temperature changestemperature changes
But also open to the air so But also open to the air so sensitive to other variables sensitive to other variables (e.g., Air Pressure)(e.g., Air Pressure)
validity problemvalidity problem
Problems with Air ThermoscopesProblems with Air Thermoscopes
No scale – so a qualitative instrumentNo scale – so a qualitative instrument Construct contamination - ValidityConstruct contamination - Validity
open to the air so sensitive to other open to the air so sensitive to other variables (e.g., Air Pressure)variables (e.g., Air Pressure)
What liquid to use? (water, spirits, What liquid to use? (water, spirits, quicksilver)quicksilver) State changes, sensitivity and linearity of State changes, sensitivity and linearity of
expansion ratesexpansion rates No standardized construction so other No standardized construction so other
instruments are not equivalent instruments are not equivalent Inaccurate conceptualization of heatInaccurate conceptualization of heat
Fix the validity problemsFix the validity problems Seal the thermoscopeSeal the thermoscope
Duke Ferdinand II (1632)Duke Ferdinand II (1632) Pascal (1663) proved that air pressure Pascal (1663) proved that air pressure
caused errors in open air thermometerscaused errors in open air thermometers Are measurement errors reliability or validityAre measurement errors reliability or validity
Use quicksilver (i.e., mercury)Use quicksilver (i.e., mercury) FareinheitFareinheit
Fix the scaling problemsFix the scaling problems Many individuals developed scales to assign numbers to the Many individuals developed scales to assign numbers to the
level of liquid in the level of liquid in the thermometerthermometer (now a thermo – meter)! (now a thermo – meter)! Newton (1700)Newton (1700)
""zeroth degree of heat" as melting snow and "33 degrees of zeroth degree of heat" as melting snow and "33 degrees of heat" as boiling waterheat" as boiling water
Rømer (1708)Rømer (1708) RéaumurRéaumur (1731) (1731)
freezing point of water is 0 degrees, the boiling point 80 freezing point of water is 0 degrees, the boiling point 80 degrees degrees
Fareinheit (1724)Fareinheit (1724) 0 as the melting point of an equal mixture of ice and salt and 0 as the melting point of an equal mixture of ice and salt and
96 as blood heat96 as blood heat Delisle (1732)Delisle (1732)
2400 graduations: 0 degrees as the boiling point and 150 2400 graduations: 0 degrees as the boiling point and 150 degrees as the freezing point of water. degrees as the freezing point of water.
Celcius (1742)Celcius (1742) freezing point of water at 0 °C and the boiling point at 100 °C freezing point of water at 0 °C and the boiling point at 100 °C
Proliferation of ScalesProliferation of Scales
UnitsUnits These scales result in “degrees” or These scales result in “degrees” or
unitsunits
What are some psychological units?What are some psychological units?
Check out these physical units!Check out these physical units! http://www.unc.edu/~rowlett/units/http://www.unc.edu/~rowlett/units/
Comparison of temp. scalesComparison of temp. scales
290944211823−814010440998055265800The surface of the Sun
8831334550−23523494303416681941Titanium melts
6080330671.67212100373.15Water boils (at standard pressure)
26.92529.612.2194.5557.998.236.8310.0Average human body temperature
7.500150491.67320273.15Water freezes (at standard pressure)
−1.83−14.22−5.87176.67459.670−17.78255.37Fahrenheit's ice/salt mixture
−135.90−218.52−90.14²559.7250−459.67−273.150Absolute zero
RømerRéaumurNewtonDelisleRankineFahrenheitCelsiuskelvin
Transformations to Equate scalesTransformations to Equate scales
[K] = 373.15 − [°De] · 2/3[°De] = (373.15 − [K]) · 3/2Delisle
[K] = ([°Rø] − 7.5) · 40/21 + 273.15[°Rø] = ([K] − 273.15) · 21/40 + 7.5Rømer
[K] = [°N] · 100/33 + 273.15[°N] = ([K] − 273.15) · 33/100Newton
[K] = [°Ré] · 5/4 + 273.15[°Ré] = ([K] − 273.15) · 4/5Réaumur
[K] = [°Ra] · 5/9[°Ra] = [K] · 9/5Rankine
[K] = ([°F] + 459.67) · 5/9[°F] = [K] · 9/5 − 459.67Fahrenheit
[K] = [°C] + 273.15[°C] = [K] − 273.15Celsius
Fix the standardization or Fix the standardization or calibration problemscalibration problems
The technology of glass blowing The technology of glass blowing made it very difficult to construct made it very difficult to construct exactly equal instruments (the size of exactly equal instruments (the size of the liquid resivoir, the amount of the liquid resivoir, the amount of liquid, the bore of the tube, etc…all liquid, the bore of the tube, etc…all must be identical to yield identical must be identical to yield identical readings.readings.
Instead, calibrate or equate using Instead, calibrate or equate using fixed reference pointsfixed reference points
Royal Society thermometersRoyal Society thermometers
Theoretical UnderstandingTheoretical Understanding The various scales of measurement and The various scales of measurement and
the calibration of thermometers to fixed the calibration of thermometers to fixed points allowed systematic investigationspoints allowed systematic investigations
That resulted in improved understanding That resulted in improved understanding of what thermometers measure (heat)of what thermometers measure (heat)
Kelvin’s scale of temperature (1848)Kelvin’s scale of temperature (1848) Rational scale with absolute zeroRational scale with absolute zero Based on gas laws and carnot cyclesBased on gas laws and carnot cycles Adopted in 1954!Adopted in 1954!
Example 2: pH - Acids & BasesExample 2: pH - Acids & Bases In the beginning there was … In the beginning there was …
perceptionperception Greeks attempted to characterize natureGreeks attempted to characterize nature One fundamental character of nature One fundamental character of nature
was taste.was taste. SaltySalty Sour Sour
the greek word for sour is the base of our word the greek word for sour is the base of our word for acidfor acid
BitterBitter SweetSweet
Acids and BasesAcids and Bases Next, it turned out that sour tasting Next, it turned out that sour tasting
substances had other regular substances had other regular propertiesproperties changes the color of litmus (a dye changes the color of litmus (a dye
extracted from a lichen commonly extracted from a lichen commonly known as dyer's weed.) known as dyer's weed.)
Corrodes metalsCorrodes metals
No real understanding of acidsNo real understanding of acids
AcidsAcids Huge proliferation of acid types (named by Huge proliferation of acid types (named by
the method used to form the acid)the method used to form the acid) Muratic acid, acetic acid, sulphuric acid, Muratic acid, acetic acid, sulphuric acid,
hydrofluoric acid, phosphoric acid, pyruvic acidhydrofluoric acid, phosphoric acid, pyruvic acid
No clear picture of the cause for the No clear picture of the cause for the common functioning of acidscommon functioning of acids LavoisierLavoisier (1776) thought it was oxygen that (1776) thought it was oxygen that
caused substances to be acidiccaused substances to be acidic Greek word Greek word oxeinoxein meaning 'sour' and meaning 'sour' and gennangennan
meaning 'to generatemeaning 'to generate
AcidsAcids Leibig (1850s) noticed that all acids Leibig (1850s) noticed that all acids
have hydrogen in commonhave hydrogen in common This insight required knowledge of the This insight required knowledge of the
elements, molecules, and weights of elements, molecules, and weights of molecules (another measurement molecules (another measurement problem)problem)
Sorenson (1909) – developed the Sorenson (1909) – developed the scale for indexing the activity of scale for indexing the activity of hydrogen in a substancehydrogen in a substance
AcidsAcids pH = (power of hydrogen ) is a pH = (power of hydrogen ) is a
measure of the activity of hydrogen measure of the activity of hydrogen ions (H+) in a solutionions (H+) in a solution
Log of number of HLog of number of H+ molecules in a molecules in a substance substance
pH value has no unit but it is not an pH value has no unit but it is not an arbitrary scalearbitrary scale
The number arises from a definition based The number arises from a definition based on the activity of hydrogen ions in the on the activity of hydrogen ions in the solution – has an absolute zerosolution – has an absolute zero
Measurement of pHMeasurement of pH Many ways now exist to measure pH.Many ways now exist to measure pH. Early measurements were based on the Early measurements were based on the
color of a substance resulting from a color of a substance resulting from a chemical reactionchemical reaction
pH indicatorpH indicator A A pH indicatorpH indicator is a is a halochromichalochromic chemical chemical
compoundcompound that is added in small amounts to a that is added in small amounts to a solutionsolution so that the so that the pHpH of the solution can be of the solution can be determined easily. Hence a pH indicator is a determined easily. Hence a pH indicator is a chemicalchemical detector for detector for protonsprotons ( (HH+). Normally, +). Normally, the indicator causes the the indicator causes the colorcolor of the solution to of the solution to change depending on the pH.change depending on the pH.
-Wilkpedia -Wilkpedia
pH MeasurementpH Measurement
yellow11.4-13.0blueIndigo carmine
orange-red10.1-12.0yellowAlizarin Yellow R
blue9.4-10.6colorlessThymolphthalein
pink8.2-10.0colorlessPhenolphthalein
blue8.0-9.6yellowThymol blue
red6.6-8.0yellowPhenol red
blue4.5-8.3redLitmus (Azolitmin)
yellow4.2-6.3redMethyl red
red3.0-5.2blueCongo red
yellow2.9-4.0redMethyl yellow
yellow1.2-2.8redThymol blue
blue-violet0.0-1.6yellowMethyl violet
Color - high pHTransition pH rangeColor -
low pHIndicator
pH MeasurementpH Measurement Adding the indicator does not result Adding the indicator does not result
in an absolute shift from one color to in an absolute shift from one color to the other.the other.
Instead, it is a gradual shift and the Instead, it is a gradual shift and the resulting color must be compared to resulting color must be compared to a SCALE to determine the pH.a SCALE to determine the pH.
Scaling pH IndicatorsScaling pH Indicators
pH and IRT similaritiespH and IRT similarities The colormetric approach to pH has a The colormetric approach to pH has a
great deal of overlap with current great deal of overlap with current Item Response approaches to Item Response approaches to measurement – IRTmeasurement – IRT
Keep this in mind when we get to IRTKeep this in mind when we get to IRT
More History of MeasurementMore History of Measurement Representational Measurement Representational Measurement
TheoryTheory Use numbers to “represent” the amount Use numbers to “represent” the amount
of an object characteristic (e.g., weight) of an object characteristic (e.g., weight) Counting in agriculture – how many Counting in agriculture – how many
cows?cows? This simple and natural use of This simple and natural use of
numbers introduced a huge problem numbers introduced a huge problem in the theory of measurementin the theory of measurement Numbers have specific propertiesNumbers have specific properties Do the quantities we want to measure Do the quantities we want to measure
have these same properties?have these same properties?
Properties of numbersProperties of numbers Order/monotonicityOrder/monotonicity CommutativityCommutativity
A + B = B + AA + B = B + A AssociativityAssociativity
(A + B) + C = A + (B + C)(A + B) + C = A + (B + C) TransitivityTransitivity
If A = B and B = C then A = CIf A = B and B = C then A = C
Representational Measurement Representational Measurement TheoryTheory
Helmholtz (1887) and HHelmholtz (1887) and Höölder (1901)lder (1901) 2 properties of measurement 2 properties of measurement
Binary combination operation= Binary combination operation= ºº Ordering relation = ≥Ordering relation = ≥
Weight orderingWeight ordering Balance scaleBalance scale
Length orderingLength ordering RodsRods
Extensive vs. Derived Extensive vs. Derived MeasurementMeasurement
Extensive MeasurementExtensive Measurement Based on addition rule for combinationBased on addition rule for combination Ex: distance, mass, timeEx: distance, mass, time
Derived Measurement:Derived Measurement: Created by mathematical operations Created by mathematical operations
using functions of extensive measuresusing functions of extensive measures Ex: velocity = distance / time (speed of Ex: velocity = distance / time (speed of
light meters per second) , Newtonian light meters per second) , Newtonian constant of gravitation, etc.constant of gravitation, etc.
History of MeasurementHistory of Measurement Campbell (1920; 1940) argued that Campbell (1920; 1940) argued that
psychological measurement was psychological measurement was impossibleimpossible1.1. Prerequisite of measurement is some Prerequisite of measurement is some
form of empirical quantification that can form of empirical quantification that can be experimentally accepted or rejectedbe experimentally accepted or rejected
2.2.Only known form of such quantification Only known form of such quantification that satisfies the axioms of extensive that satisfies the axioms of extensive measurement is the binary operation of measurement is the binary operation of concatenationconcatenation
3.3.Psychology has no extensive Psychology has no extensive measurement measurement
History of MeasurementHistory of Measurement Stevens (1951) argued that this Stevens (1951) argued that this
perspective on measurement was too perspective on measurement was too narrownarrow Various levels or types of measurementVarious levels or types of measurement
Table 1, Stevens 1946, page 678)Table 1, Stevens 1946, page 678)
Scales of MeasurementScales of MeasurementScale Basic Operations Mathematical Group Permissible Statistics
Nominal Determination of Equality
Ordinal Determination of Order
Interval
Ratio Coefficient of variation
Permutation Group – one to one substitution Num ber of cases; mode
Isotonic Group – Monotonic function
Median, percentiles, Range
Determination of Equality of Differences
General linear group xt = ax + b
MeanStandard deviationRank-order correlationProduct-moment correlation
Determination of Equality of Ratios Similarity Group xt = ax
History of MeasurementHistory of Measurement Luce, Narens, TverskyLuce, Narens, Tversky
Conjoint polynomial measurementConjoint polynomial measurement Proved that additivity (interval scaling) Proved that additivity (interval scaling)
can be obtained by using transformations can be obtained by using transformations of two variables that are on an ordinal of two variables that are on an ordinal scalescale
Causality and MeasurementCausality and Measurement Measurement requires causal Measurement requires causal
inferenceinference Changes in the level of the latent entity Changes in the level of the latent entity
cause changes in the level of the cause changes in the level of the indicator variable(s).indicator variable(s).
This inference requires the same This inference requires the same scientific method as any causal research scientific method as any causal research question.question.
Must show that the latent variable is the Must show that the latent variable is the only cause of the indicator (construct only cause of the indicator (construct validity)validity)
ConstructsConstructs What is a construct?What is a construct? Constructs become better defined via Constructs become better defined via
researchresearch Temperature, pH, bacteria, gas pressure, Temperature, pH, bacteria, gas pressure,
electricityelectricity 1. An unobserved 1. An unobserved causecause of variation of variation
in an observable variable(s)in an observable variable(s) 2. A label used to describe a pattern of 2. A label used to describe a pattern of
observed covariancesobserved covariances
Model of MeasurementModel of Measurement
Construct
Construct = an unobservable but real causal variable(aka latent variable)
Indicator / Instrument
Indicator = an observable variable thatis solely caused by the construct andsensitive to changes in the level of the construct
Scale: the rule for assigning numbers to the levels of theindicator or instrument
Key Assumptions for classKey Assumptions for class Psychological Constructs are realPsychological Constructs are real
Reflect actual properties or Reflect actual properties or characteristics of peoplecharacteristics of people
Not just a descriptive listing of Not just a descriptive listing of correlatescorrelates
Measurement error reflects the effect Measurement error reflects the effect of non-random nuisance variablesof non-random nuisance variables No such thing as random measurement No such thing as random measurement
error!error!
What’s your construct?What’s your construct? Over the next week, your primary job Over the next week, your primary job
is to identify a construct/variable that is to identify a construct/variable that interests you.interests you. Feel free to think outside the box!Feel free to think outside the box! Identify some behavior or human Identify some behavior or human
process that interests you and then process that interests you and then think about the cause of that behavior. think about the cause of that behavior. The cause is the construct.The cause is the construct.
Some quotes to think aboutSome quotes to think about "Psychometry, it is hardly necessary to say, means the art of "Psychometry, it is hardly necessary to say, means the art of
imposing measurement and number upon operations of the imposing measurement and number upon operations of the mind...".Galton, 1879. mind...".Galton, 1879.
"I often say that when you can measure what you are speaking "I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind: it may be your knowledge is of a meagre and unsatisfactory kind: it may be the beginning of knowledge, but you have scarcely, in your the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science, whatever the matter may thoughts, advanced to the stage of science, whatever the matter may be.“ Sir William Thomson, Lord Kelvin. 1889 be.“ Sir William Thomson, Lord Kelvin. 1889
““Whatever exists at all, exists in some amount. To know it Whatever exists at all, exists in some amount. To know it thoroughly involves knowing its quality as well as its quantity” thoroughly involves knowing its quality as well as its quantity” Thorndike, 1918Thorndike, 1918