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7/27/2019 Mesurement and Scaling ppt
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MEASUREMENT AND
SCALING
Prof M. R. Suresh
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Measurement: defined as a standardizedprocess of assigning numbers or other
symbols to certain characteristics of objects ofinterest according to prespecified rules.
important as statistical analyses can be done
on appropriate scalestwo characteristics:
one-to-one correspondence between the
symbol and the characteristic (in the object)
being measured
rules of assignment must be invariant over
time
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Scaling is a process of creating a continuumon which objects are located according to the
amount of measured characteristic theypossess
Type of Scale Statistical Tests
Nominal Percentage, mode, chi-square
Ordinal Percentile, median Rank-OrderCorrelation Friedmans ANOVA
Interval Mean, , t-test, ANOVA,Regression analysis correlation
Ratio G.M, H.M. coefficient of variation
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Nominal Scale
objects are assigned to mutually exclusive,
labeled categoriesE.g. Male, female,Geographical area
if one entity is assigned the same number asanother, they are identical with respect to anominal variable
Ordinal Scale
obtained by ranking objects or arranging
them in order with respect to some commonvariable
E.g. Ranks of students, seniors, juniors in acollege
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Interval Scale
in this the numbers used to rank the objects
represent equal increments of attribute being
measureddifferences can be compared
difference between 2 & 3 same as 6 & 7 but half thedifference between 2 and 4
no absolute zero
E.G of interval scale: attitude measures, indices, temperaturescales
Ratio Scalemeaningful zero point
makes comparisons in absolute magnitude
measuring public opinion
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Issues in Designing Single itemScales
1. Number of scale categories 2 to capability, format, object attribute
2. Types of poles
verbal descriptors as endpoints
e.g. sweet ----- not sweet
3. Strength of anchors
extremely colorful, very colorful4. Labeling
5. Balancing
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Single Item Scales
only one item to measure a construct
1. Itemized category scale
Satisfaction with present healthinsurance plan
- very satisfied
- quite satisfied
- somewhat satisfied
- not at all satisfied
Very satisfied Very dissatisfied
+2 +1 0 -1 -2
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2. Comparative scales
E.g.
Rank-Order Scales
require respondents to arrange a set ofobjects with respect to common criterion
Two problems forced to make a choice,undifferentiated middle
Constant sum scale
Limitation only a few categoriesQ sort scaling
Paired comparison
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Multiple Item Scales
Objects have many facets
Likert scale also known as summated scaledegree of agreement/disagreement on avariety of statements
two parts : item part, evaluative part
important assumption: single common factor
Thurstone scale also called equal appearingintervals group of judges are given 75 to 100
items degree of favourableness (11 categorybipolar)
scale value of each items is the median valueassigned by judges complicated
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Semantic Differential widely used
e.g. images of competing brands preference of
bipolar scales pairs of objects/phrases correspond toproduct/service attributes -ve or unfavorable polerotated treated as interval scales, group mean valuescalculated
specific information can be lost
Unipolar +3/ +2/ +1
Tangy -1/ -1/ -1
Associative scaling
Appropriate for choice situation in a sequentialdecision process trade offs not captured reducedvalidity
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Guidelines for developing multi-itemscale
1. Determine what you want to measure
2. Generate as many items as possible
3. Experts evaluation of initial pool of items
4. Determine type of attitudinal scale to be
used
5. Include validation items
6. Administer items to an initial sample7. Refine
8. Optimize scale length
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Choice of an attitudinal scale
specific info required to satisfy
research objectives
adaptability of scale to datacollection method, budget
compatibility to respondent
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Accuracy of attitude measurements
True Score ModelXO = XT + XS (affects in a constant way)+ XR(transient factor {situational})
Validity
Content/face validity:subjective but
systematic evaluation of how well thecontent of a scale represents themeasurement task
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Criterion validity: reflects whether
a scale performs as expected inrelated to other variables selected(criterion)
concurrent validity
predictive validity
Construct Validity
convergent validity
discriminant validity
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Reliability
test retestsplit half
Sensitivity: ability to discriminate
among meaningful differences inaltitudes
Generalisability
RelevancyRelevance = reliability X validity
International MR