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Chapter 6
Indexes, Scales, and
The terms index and scale are typically used
imprecisely and interchangeably in social
research literature.
 Both
scale and indexes are ordinal
measures of variables.
 Both rank-order the units of analysis in
terms of specific variables such as
religiosity, alienation, socioeconomic
status, prejudice.
 Both
scales and indexes are composite
measures of variables – that is,
measurements based on more than one
data item.
 Eg. A survey
respondent’s score on an
index or scale of religiosity is determined
by the response given to several
questionnaire items, each of which
provides some indication of religiosity
 An
index is constructed by simply
accumulating scores assigned to individual
attributes. We might measure prejudice,
for example, by adding up the number of
prejudiced statements each respondent
agreed with
A scale is constructed by assigning scores to
patterns of responses, recognizing that some
items reflect a relatively weak degree of the
variable while others reflect something stronger
 Scales are generally superior to indexes,
because scales take into consideration the
intensity with which different items reflect the
variable being measured
 Scale scores convey more information than
index scores
Index Construction
 Selecting
possible items
 Examining their empirical relationships
 Scoring the index
 Validating it
Item Selection
Face validity
 the
first criterion for selecting items to be
included in the index is face validity (or
logical validity).
 if you want to measure political
conservatism, for example, each of your
items should appear on its face to indicate
Item Selection
 the
methodological literature on
conceptualization and measurement
stresses the need for unidimensionality in
scale and indexes construction
composite measure should represent
only one dimension of a concept
Item Selection
General or Specific
 the
general dimension you’re attempting to
measure may have many nuances
 in the example of religiosity, the indicators
– ritual participation, belief – represent
different types of religiosity
Item Selection
the amount of variance that is provided by items
 to have variance, you have two options
 first – you may select several items the
responses to which divide people about equally
in terms of the variable
 second- select items differing in variance – one
item might identify about half the subjects as
conservative, while another might identify few of
the respondents as conservatives
Examining of Empirical
 Response
to one question will help us
predict how that respondent will answer on
other questions
 Bivariate relationships
 Multivariate relationships
Index Scoring
 Decide
the range of index scores
 See how many cases, questions, for each
point in the scale
 Assigning scores for each particular
response – usually weighted equally
unless there is a reason for heavier weight
for a case
Handling Missing Data
 Exclude
the cases
 Treat it as one of the existing responses
 Don’t know answers
 Assign middle value
 proportions
Index Validation
Item analysis (internal validation) – you examine
the extent to which the index is related to (or
predicts responses to) the individual items it
 if the index adequately measures a given
variable, it should successfully predict other
indications of that variable
 External validation – people scored as politically
conservative on an index should appear
conservative by other measures as well, such as
their responses to other items in the
Scale Construction
 Scales
offer more assurance of ordinality
by tapping the intensity structures among
the indicators
Bogardus Social Distance Scale
is a measurement technique for determining the
willingness of people to participate in social
relations – of varying degrees of closeness –
with other kinds of people
 if a person is willing to accept a given kind of
association, he or she would be willing to accept
all those preceding it in the list – those with
lesser intensities
 more people agree to the easy items than to the
hard ones
 logic demands that once a person has refused a
relationship presented in the scale, he or she will
also refuse all the harder ones that follow it
Thurstone Scales
an attempt to develop a format for generating
groups of indicators of a variable that have at
least an empirical structure among them
 each judge is asked to estimate how strong an
indicator of a variable each item is by assigning
scores of perhaps 1-13
 once the judges have completed this task, the
researcher examines the scores assigned to
each item by all the judges to determine which
items produced the greatest agreement among
the judges
Likert Scale
contains responses strongly agree,
agree, disagree, and strongly disagree
Semantic Differential
 asks
questionnaire respondents to choose
between two opposite positions using
qualifiers to bridge the gap between the
two opposites
 you need to find two opposite terms,
representing the polar extremes along
each dimensions
Semantic Differential
Feelings about musical selections:
Very much somewhat neither somewhat very much
Guttman Scale
based on the fact that some items under
consideration may prove to be more extreme
indicators of the variable than others
 begin by examining the face validity of items
available for analysis – then you would examine
the bivariate and perhaps multivariate relations
among those items
 also look at hard and easy indicators of the
variable being examined
 based on the notion that anyone who gives a
strong indicator of some variable will also give
the weaker indicators
 Summarize
the intersection of two or more
concepts or variables, creating a category
or type – nominal variable