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MASH : Maths and Stats Help

Cronbach's Alpha (α)

Introduction

Cronbach's Alpha is a measure of internal consistency/reliability. It is commonly used to determine the reliability of a scale comprised of multiple Likert questions in a survey/questionnaire. Many different thresholds are used to determine an appropriate reliability value, in the Table below you can see a selection of values from Cohen et al., (2018).

Cronbach's Alpha Thresholds
0.90 or more Very highly reliable
0.80–0.90 Highly reliable
0.70–0.79 Reliable
0.60–0.69 Marginally/minimally reliable
0.60 or less Unacceptably low reliability

Values from Page 744; Cohen, L., Manion, M., & Morrison, M. (2018) Research Methods in Education (8th ed.). Routledge.

 

Test Procedure

  1. Click Analyze > Scale > Reliability Analysis

    Screenshot Illustrating the options to calculate Cronbach's Alpha (Click Analyze then Scale then Reliability Analysis)

  2. Within the 'Reliability Analysis' window, select all of the variables you wish to analyse and move them to the 'Items' Box. Ensure that the model says 'Alpha', this is the default option. Then click OK.

    Screenshot showing all four items moved over to the 'Items' box.

 

Results

SPSS will generate two tables, for this test we only need one table the Reliability Statistics

Screenshot showing the SPSS outputs of the Cronbachs Alpha, the value 0.834 is highlighted in yellow.

 

 

Reliability Statistics 

This table shows the specific test result being Cronbach's Alpha (α) and the number of items (N) that comprise the scale.

Reporting the Results in APA Formatting

A questionnaire was given to all students consisting of 4 items measuring Evaluation Ability, the value for Cronbach’s Alpha for the survey was α = .83, indicating the scale is "Highly Relaible" (Cohen et al., 2018, p.744)