International Journal of Public Health

, Volume 58, Issue 4, pp 637–642 | Cite as

The reliability of a two-item scale: Pearson, Cronbach, or Spearman-Brown?

  • Rob Eisinga
  • Manfred te Grotenhuis
  • Ben Pelzer
Hints & Kinks


To obtain reliable measures researchers prefer multiple-item questionnaires rather than single-item tests. Multiple-item questionnaires may be costly however and time-consuming for participants to complete. They therefore frequently administer two-item measures, the reliability of which is commonly assessed by computing a reliability coefficient. There is some disagreement, however, what the most appropriate indicator of scale reliability is when a measure is composed of two items. The most frequently reported reliability statistic for multiple-item scales is Cronbach’s coefficient alpha and many researchers report this coefficient for their two-item measure (Cuijpers et al. 2009; Löwe et al. 2005; Michal et al. 2010; Young et al. 2009). Others however claim that coefficient alpha is inappropriate and meaningless for two-item scales (Sainfort and Booske 2000; Verhoef 2003; Cramer et al. 2006; O’Brien et al. 2008). Instead, they recommend using the Pearson correlation...


Coefficient Alpha True Score Local Dependence Classical Test Theory True Reliability 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The authors are grateful to William Revelle and an anonymous reviewer for helpful comments on a previous version of this manuscript and suggestions for improvements.


  1. Bollen KA (1989) Structural equations with latent variables. Wiley, New YorkGoogle Scholar
  2. Cramer ME, Atwood JR, Stoner JA (2006) Measuring community coalition effectiveness using the ICE© instrument. Public Health Nurs 23:74–87PubMedCrossRefGoogle Scholar
  3. Cuijpers P, Smits N, Donker T, ten Have M, de Graaf R (2009) Screening for mood and anxiety disorders with the five-item, the three-item, and the two-item mental health inventory. Psychiat Res 168:250–255CrossRefGoogle Scholar
  4. Embretson SE, Reise SP (2000) Item response theory for psychologists. Lawrence Erlbaum Associates, MahwahGoogle Scholar
  5. Emons WHM, Sijtsma K, Meijer RR (2007) On the consistency of individual classification using short scales. Psychol Methods 12:105–120PubMedCrossRefGoogle Scholar
  6. Hancock GR, Mueller RO (2001) Rethinking construct reliability within latent variable systems. In Cudeck R, Du Toit S, Sörbom D (Eds), Structural equation modeling: present and future. A festschrift in honor of Karl Jöreskog. Scientific Software International, Lincolnwood, pp 195–216Google Scholar
  7. Herbert W, Marsh HW, Hau K-T, Balla JR, Grayson D (1998) Is more ever too much? The number of indicators per factor in confirmatory factor analysis. Multivar Behav Res 33:181–220CrossRefGoogle Scholar
  8. Hulin C, Netemeyer R, Cudeck R (2001) Can a reliability coefficient be too high? J Consum Psychol 10:55–58CrossRefGoogle Scholar
  9. Little TD, Lindenberger U, Nesselroade JR (1999) On selecting indicators for multivariate measurement and modeling with latent variables: when ‘good’ indicators are bad and ‘bad’ indicators are good. Psychol Methods 4:192–211CrossRefGoogle Scholar
  10. Lord FM, Novick MR (1968) Statistical theories of mental test scores. Reading, Addison-WesleyGoogle Scholar
  11. Löwe B, Kroenke K, Gräfe K (2005) Detecting and monitoring depression with a two-item questionnaire (PHQ-2). J Psychosom Res 58:163–171PubMedCrossRefGoogle Scholar
  12. Michal M, Zwerenz R, Tschan R, Edinger J, Lichy M, Knebel A, Tuin I, Beutel M (2010) Screening for depersonalization-derealization with two items of the Cambridge depersonalization scale. Psychother Psych Med 60:175–179CrossRefGoogle Scholar
  13. O’Brien M, Buikstra E, Hegney D (2008) The influence of psychological factors on breastfeeding duration. J Adv Nurs 63:397–408PubMedCrossRefGoogle Scholar
  14. Revelle W, Zinbarg RE (2009) Coefficients alpha, beta, omega, and the GLB: comments on Sijtsma. Psychometrika 74:145–154CrossRefGoogle Scholar
  15. Rüsch N, Corrigan PW, Wassel A, Michaels P, Olschewski M, Wilkniss S, Batia K (2009) A stress-coping model of mental illness stigma. I. Predictors of cognitive stress appraisal. Schizophr Res 110:59–64PubMedCrossRefGoogle Scholar
  16. Sainfort F, Booske BC (2000) Measuring post-decision satisfaction. Med Decis Mak 20:51–61CrossRefGoogle Scholar
  17. Sijtsma K (2009) On the use, the misuse, and the very limited usefulness of Cronbach’s alpha. Psychometrika 74:107–120PubMedCrossRefGoogle Scholar
  18. Verhoef PC (2003) Understanding the effect of customer relationship management efforts on customer retention and customer share development. J Mark 67:30–45CrossRefGoogle Scholar
  19. Young J, Jeganathan S, Houtzager L, Di Guilmi A, Purnomo J (2009) A valid two-item food security questionnaire for screening HIV-1 infected patients in a clinical setting. Public Health Nutr 12:2129–2132PubMedCrossRefGoogle Scholar

Copyright information

© Swiss School of Public Health 2012

Authors and Affiliations

  • Rob Eisinga
    • 1
  • Manfred te Grotenhuis
    • 1
  • Ben Pelzer
    • 1
  1. 1.Radboud University NijmegenNijmegenNetherlands

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