Survey research and design in psychology/Tutorials/Psychometrics/Internal consistency

This tutorial involves learning how to examine internal consistency using SPSS's reliability function.

To examine the internal consistency of a set of related items:
 * 1) Recode if necessary so that all items are scored in the same direction
 * 2) Compute the Cronbach's alpha (α) and examine the reliability analysis results (especially Cronbach's alpha if item removed) to determine the internal consistency and whether any items should be dropped
 * 3) Recompute the reliability analysis after dropping any unwanted items
 * 4) Note that the example involves only 10 items to measure one factor. If you have a multi-factorial measure, then examine the internal consistency for each set of items which represent a factor.

Exercise 1: Openness
Data file: data_15_1.sav Allen and Bennett 15.2, pp. 205-213

Rating scale

Items


 * Openness reliability analysis.

compute Open2r=6-Open2. compute Open4r=6-Open4. compute Open6r=6-Open6. compute Open8r=6-Open8. compute Open10r=6-Open10. EXECUTE.
 * Recoding.

variable labels Open2r 'O2. Tend to vote for conservative political candidates.' Open4r 'O4. Avoid philosophical discussions.' Open6r 'O6. Do not like art.' Open8r 'O8. Am not interested in abstract ideas.' Open10r 'O10. Do not enjoy going to art museums.'.


 * Reliability.

RELIABILITY /VARIABLES=Open1 Open2r Open3 Open4r Open5 Open6r Open7 Open8r Open9 Open10r /SCALE('ALL VARIABLES') ALL /MODEL=ALPHA /STATISTICS=CORR /SUMMARY=TOTAL.

RELIABILITY /VARIABLES=Open1 Open2r Open3 Open4r Open6r Open7 Open8r Open9 Open10r /SCALE('ALL VARIABLES') ALL /MODEL=ALPHA /STATISTICS=CORR /SUMMARY=TOTAL.


 * 10 items; reverse-code 2, 4, 6, 8, 10
 * α = .77, N = 60
 * drop #5, which gives α = .84

See extra exercises