Measuring and scaling of quantitative data khalid

Measuring and Scaling of
Quantitative Data

Prof. Dr. Khalid Mahmood
University of the Punjab
Lahore-PAKISTAN

Agenda
 What are measuring and scaling?
 Levels of measurement
 Process of measurement
 Methods of scaling
 Types of scales
 Reliability and validity of scales

What are measuring and scaling?
 Measurement: The process of describing some
property of a phenomenon by assigning numbers.
 Scale: A type of composite measure composed of
several items that have a logical or empirical
structure among them. It allows to measure the
intensity or direction of a construct by aligning the
responses on a continuum.

“If a thing exists, it exists in some amount; and if
it exists in some amount, it can be measured.”
–E. L. Thorndike (1914)

Levels of measurement
 Nominal
 Ordinal
 Interval
 Ratio

Nominal
 A categorical variable, also called a nominal
variable, is for mutual exclusive, but not ordered,
categories.
 Nominal scales are mere codes assigned to objects
as labels, they are not measurements.
 Not a measure of quantity. Measures identity and
difference. People either belong to a group or they
do not.
 Sometimes numbers are used to designate
category membership.
 Examples: Gender, eye color, marital status

Ordinal
 This scale has the ability to rank the individual
attributes of two items in same group but unit
of measurement is not available in this scale,
like student A is taller than student B but their
actual heights are not available.
 Designates an ordering: greater than, less
than.
 Does not assume that the intervals between
numbers are equal.

Interval
 Classifies data into groups or categories
 Designates an equal-interval ordering
 The difference in temperature between 20 degrees
Fo and 25 degrees Fo is the same as the difference
between 76 degrees Fo and 81 degrees Fo
 Zero point on the interval scale is arbitrary zero, it
is not the true zero point
 Common IQ tests are assumed to be interval
measures

Ratio
 This is the highest level of measurement and has
the properties of other three levels; coupled with
fixed origin or zero point.
 Measurements of heights of students in a class
(zero means complete lack of height).
 Someone 6 ft tall is twice as tall as someone 3 feet
tall.
 Heart beats per minute has a very natural zero
point. Zero means no heart beats.

Process of measurement
 Define concepts to be measured
 Define attributes of the concepts
 Select level of measurement (data type)
 Generate items/questions
 Wording
 Response format
 Layout and design questionnaire
 Pretest and refine

Methods of scaling
 Rating scales
 Have several response categories and
are used to obtain responses with regard
to the object, event, or person studied.
 Ranking scales
 Make comparisons between or among
objects, events, persons and obtain the
preferred choices and ranking among
them.

Types of scales
 Likert scale
 Semantic differential scale
 Stapel scale
 Graphic rating scale
 Thurstone scale
 Guttman scale
 Paired comparison scale
 Forced choice
 Comparative scale

Likert scale
 Is designed to examine how strongly subjects agree or
disagree with statements on a 5-point scale.

Semantic differential scale
 Several bipolar attributes are identified at the
extremes of the scale, and respondents are
asked to indicate their attitudes.

Stapel scale
 This scale simultaneously measure both
the direction and intensity of the
attitude toward the items under study.
 It is a slight modification of semantic
differential scale.
 The scale consists of a single adjective
in the middle of positive and negative
numbers

Graphic rating scale
 A graphical representation helps the
respondents to indicate their answers to
particular question by placing a mark at
the appropriate point on the line.

Thurstone scale
 This technique assesses the extent of agreement
among a group of judges about the proposed items
for a scale.
 For example, one might ask a group of persons to
judge how closely 25 different items come to
measuring self-esteem. Then, one might select
the 10 items that received the highest average
scores for having content validity with self-esteem.
 It can help find the best questions to ask to
measure an abstract concept.
 It does not specify how a question or set of
questions should be formatted on a questionnaire.

Guttman scale
 Who agrees with an item will also agree with all other
items expressing a less extreme position
 Using a series of statements to reflect the strength of
attitudes

“I think the following contains
SubjectC
pornographic materials.”
A B Scale
Adult movies rated [Yes] [Yes [Yes Value
XXX ] ] 4
Pla y bo y magazine [Yes] [Yes [No] 3
]
Lingerie ads [Yes] [No] [No] 2
N w Yo rk Tim e s
e [No] [No] [No] 1
-

Paired comparison scale
 The respondents are asked to
choose between two objects at a
time.

Forced choice
 Enables respondents to rank
objects relative to one another,
among the alternatives provided.

Comparative scale
 Provides a benchmark or a point of
reference to assess attitudes toward the
current object, event, or situation under
study.

Reliability of scale
 Indicates the extent to which it is
without bias (error free) and hence
ensures consistent measurement across
time and across the various items in the
instrument.

Types of reliability
 Stability of measures
 Test-retest reliability
 Parallel-form reliability
 Internal consistency of measures
 Inter-item consistency reliability
 Cronbach’s alpha
 Split-half reliability

Validity of scale
 Ensures the ability of a scale to indeed
measure the concept we want to
measure and not something else.

 Content validity
 Criterion related validity
 Construct validity

Content validity
 Ensures that the measure includes an
adequate and representative set of
items that tap the concept.
 A panel of judges

Criterion related validity
 Is established when the measure
differentiates individuals on a criterion
it is expected to predict.
 Concurrent validity: established when the
scale differentiates individuals who are
known to be different
 Predictive validity: indicates the ability of
measuring instrument to differentiate
among individuals with reference to
future criterion

Construct validity
 Testifies to how well the results obtained from
the use of the measure fit the theories around
which the test is designed.
 Convergent validity: established when the scores
obtained with two different instruments measuring
the same concept are highly correlated
 Discriminant validity: established when, based on
theory, two variables are predicted to be
uncorrelated, and the scores obtained by measuring
them are indeed empirically found to be so

Measuring and scaling of quantitative data khalid

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Measuring and scaling of quantitative data khalid (20)

More from Khalid Mahmood (20)

Measuring and scaling of quantitative data khalid