Mesurement and Scaling ppt

7/27/2019 Mesurement and Scaling ppt

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MEASUREMENT AND

SCALING

Prof M. R. Suresh


2/15

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


3/15

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


4/15

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


7/15

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


10/15

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


11/15

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


14/15

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

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Mesurement and Scaling ppt