Scales and Indices

Scales and Indices combine several categories in a question or several questions into a “composite measure” that represents a larger concept

Uses questionnaire materials efficiently Why used?

Why Composite Measures

Cannot arrive at a single question that has closed ended answers that adequately describes a concept

Example—religion may have many aspects such as church attendance, belief in God, etc.

May want to analyze several dichotomous variables together, efficiently

Indices and Scales

Both are measures that have “rank order” Both are composites of questions or other

variables

How do they differ?

An index is constructed as a simple sum of effects or values through accumulation of scores or numbers. It is a sum of concepts.

A scale is constructed by assigning scores to a range of intensities of response. Is a measure of intensity of a single concept.

Logic of Construction

See page 150 of the text Index—each respondent type is assigned a

score based on the attribute to be scored, these are summed and a value (a number) is assigned and analysis is done on the number not the respondent type

Scale—the responses are arrayed in order of intensity of some attribute and the intensity measure (a number) is used in analysis

Index Construction

Select the items to be indexed Assign a value to each, can be weighted but

need contributory factor analysis to do this Add the number of responses with a value for

each respondent and construct an index value for the respondent

Must have face validity Unidimensional (unlike scales) Variance

Index Construction

Bivariate relationship—should be related statistically significantly related, this is a crosstab and significance testing issue

Must add something to the concept or the explanation of the concept indexed

Missing data eliminated before the index formed Must have Item validation and index validation—do

the measure and it’s components measure what they purport to and are they sufficient measures

Likert Scales

Really indices No equal measure between levels Likely, less likely, not likely format Assigned values to each level of the “scale”

and you have an equivalent to an index

Scale Construction

Ordinal ranking by intensity of a single variable

Equal importance to each rank in the scale thus a measure of intensity of the concept or the variable used to represent it

Examples—intensity of belief or attitude rather than likely/less likely format

Thurstone Scales

Measure using equal intervals Assigns scores to the intensity of a specific

concept Example 1 to 10—how happy are you right

now (0?) How prejudiced are you? Scales can have zero and negative values,

indices cannot

Guttman Scales

A type of composite measure used to summarize Several discrete and quantifiable observations and to represent some more general variable or concept

Example—scientific orientation would combine 4 questions about specific intensity attitutes and sum then for a scale of scientific orientation

Typology

Multi-dimensional arrays of attitudes or opinions

Usually independent variables arranged in a grid fashion that were originally dichotomous in nature

Uses of Scales and Indices

Example—concept of women’s empowerment

Multiple questions are involved which each discuss an aspect of women’s power to act and decide for themselves

The importance of each must first be evaluated to give a power or intensity to each

They are added and a scale (or if not intensified, an index) is born

Uses

Makes concepts out of groups of attributes or opinions, actions

Gives intensity and scalability