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Outliers and EFA Analysis

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Quantitative Research Techniques

with SPSS
Objectives

 Exploratory Factor Analysis (EFA)


 Introduction
 Assumptions of EFA
 Data Screening & Cleaning
 Missing values
 Aberrant values
 Normality & outliers
 KMO & Bartlet’s Tests
 No of factors to be retained
 Labeling the extracted factors
 Conducting EFA in SPSS
 Reporting results of EFA in a research paper

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Factor Analysis: Introduction

 It’s a data reduction technique


 Terminology
 Factor & Item
 Exploratory Factor Analysis (EFA)
 Confirmatory Factor Analysis (CFA)

 Steps Involved in EFA


 Checking suitability of data
 Factor extraction
 Factor rotation and interpretation

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Factor analysis
 This family of factor analytic techniques has a number of
different uses. It is used extensively by researchers involved in
the development and evaluation of tests and scales.

 The scale developer starts with a large number of individual


scale items and questions and, by using factor analytic
techniques, they can refine and reduce these items to form a
smaller number of coherent subscales.

 Factor analysis can also be used to reduce a large number of


related variables to a more manageable number, prior to using
them in other analyses such as multiple regression or
multivariate analysis of variance.

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Factor analysis
 Types of factor analysis
 Exploratory and confirmatory
 Confirmatory factor analysis
 Exploratory factor analysis is often used in the early stages of
research to gather information about (explore) the
interrelation-ships among a set of variables.

 Confirmatory factor analysis, on the other hand, is a more


complex set of techniques used later in the research process to
test (confirm) specific hypotheses or theories concerning the
structure underlying a set of variables.

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Missing value analysis

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Aberrant/abnormal values
 Aberrant values are those values that do not fall in the given response
categories, and it might because of typing error during data entry (Tufféry &
Riesco, 2011).

 Procedure

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Multivariate outliers
 The outlier is referred as “a case with such an extreme value on one construct (a
univariate outlier) or such a strange combination of the score on two or more
constructs (multivariable outlier)” (B. Tabachnick & L. Fidell, 2007b, p.72).
 Procedure

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Reversing negatively worded
items
 In some scales the wording of particular items has been reversed to help
prevent response bias.

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Here we go…

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Steps Involved in EFA

 Checking Suitability of Data


 Variable type must be continuous
 Minimum sample size >= 150 or 5 cases per item
 Sufficient >= .30 inter items correlations
 KMO >= .60 & Bartlet’s Test p<.05
 Factor Extraction
 Kaiser’s Criterion (Eigen value >=1)
 Catell’s Scree test (select factors above the elbow)
 Factor Rotation & Interpretation

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EFA
Hands on Experience

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Reporting Results of EFA in a Report

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Reporting Results of EFA in a Report

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Reporting Results of EFA in a Report

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Checking the reliability
of a scale
 Reliability refers the degree to which the items that make up the scale
‘hang together’. Are they all measuring the same underlying construct?
One of the most commonly used indicators of internal consistency is
Cronbach’s alpha coefficient.
 Procedure

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