Cronbach alpha interpretation

Contents

Introduction

A psychology faculty wants to examine the reliability of a personality test.

They therefore have a sample of N = 90 students fill it out.

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The data thus gathered are in big-5.sav, partly shown below.

As suggested by the variable names, our test attempts to measure the “big 5” personality traits. For other data files, a factor analysis is often used to find out which variables measure which subscales.

Anyway.

Our main research question is: what are the reliabilities for these 5 subscales as indicated by Cronbach’s alpha? But first off: what's Cronbach’s alpha anyway?

Cronbach’s Alpha - Quick Definition

Cronbach’s alpha is the extent to which the sum over 2(+)
variables measures a single underlying trait.

More precisely, Cronbach’s alpha is the proportion of variance of such a sum score that can be accounted for by a single trait. That is, it is the extent to which a sum score reliably measures something and (thus) the extent to which a set of items consistently measure “the same thing”.

Cronbach’s alpha is therefore

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