Robert A. Cummins Australian Centre on Quality of Life Deakin University

1. Measurement scales and depression Robert A. Cummins Australian Centre on Quality of Life Deakin University http://www.deakin.edu.au/research/acqol

2. Overview What are the issues under investigation? • The problem of sub-optimal response scales • The problem of sub-optimal depression sales Why are these issues important? • Likert scales are blunt instruments • We seem not to understand what depression actually is What are the implications? • Our response scales may be compromising our measurements • We may be misdiagnosing depression

3. Freyd, M. (1923). The graphic rating scale. Journal of Educational Psychology, 14, 83-102. For job interviews Does he appear neat or slovenly in his dress? “When you have satisfied yourself on the standing of this person in the trait on which you are rating him, place a check at the appropriate point on the horizontal line. You do not have to place your check directly above a descriptive phrase. You may place your check at any point on the line.” (p.88). [then standardized to 0-10]

4. Rensis Likert 1 2 3 4 5 Strongly approve Approve Undecided Disapprove Strongly disapprove Head Survey Research Center University of Michigan 1903 - 1981 Likert, R. (1932) A technique for the measurement of attitudes. Archives of Psychology, No.14, New York. Why only five levels of choice?

5. Problem #1 • People can make more than five points of discrimination. They are therefore blunt instruments, not capturing the full extent of discrimination

6. Increasing the number of choice points above 5 increases scale sensitivity • Diefenbach, M.A., Weinstein, N.D., & O’Reilly, J. (1993). Scales for assessing perceptions of health hazard susceptibility. Health Education Research, 8, 181-192. • Russell, C., & Bobko, P. (1992). Moderated regression analysis and Likert scales: Too coarse for comfort. Journal of Applied Psychology, 77, 336-342. • Jaeschke, R., & Guyatt, G.H. (1990). How to develop and validate a new quality of life instrument. In: B. Spilker (Ed.) Quality of life assessment in clinical trials (pp.47-57). New York: Raven Press.

7. Problems with Likert scales • People can make more than five points of discrimination. They are therefore blunt instruments 2. The number of choice points cannot easily be expanded because we do not have the necessary adjectives

8. Mostly dissatisfied Very unhappy Very pleased Mostly satisfied Mixed feelings Delighted Pleased Unhappy Terrible Roy Morgan Research (1993) Roy Morgan Research (1993). International values audit, 22/23 May. Melbourne: Roy Morgan Research Centre.

9. Problems with Likert scales • People can make more than five points of discrimination. They are therefore blunt instruments 2. The number of choice points cannot easily be expanded because we do not have the necessary adjectives 3. The psychometric distance between the named adjectives does not accord with the interval nature of the scale

10. Very good Poor Fair Good Excellent Actual psychometric separation 1.0 2.3 3.4 4.3 5.0 Ware and Gandek (1994) used the Thurstone method of equal-appearing intervals to calculate the following distances between category labels used in the SF-36 Ware, J. E., & Gandek, B. (1994) The SF-36 Health Survey: Development and use in mental health research and the IQOLA project. International Journal of Mental Health, 23, 49-73.

11. Louis Leon Thurstone (1887 -1955) Dept Psychology University of Chicago Jones, L.V., & Thurstone, L.L. (1955) The psychophysics of semantics: An experimental investigation. The Journal of Applied Psychology, 39(1), 31-36.

12. 11-point, end-defined scale Completely Satisfied Completely Dissatisfied Mixed 0 1 2 3 4 5 6 7 8 9 10

13. 40 35 33.1 30 25 Frequency 20 17.9 17.1 15.1 15 10 7.0 5.5 5 1.7 1.2 0.6 0.5 0.3 0 0 1 2 3 4 5 6 7 8 9 10 Response scale 0 - 10 How satisfied are you with your life as a whole? Can people reliably use 11-points of discrimination? N≈30,000

14. The relationship between SWB and depression Critical issue #2 Can the Subjective Wellbeing, or Positive Affect, be used as a measure of depression?

15. Homeostasis Set point Challenging conditions Set Point range Upper Threshold Lower Threshold SWB 50 No challenge Very strong challenge Defensive range 80 Dominant Source of SWB Control a 70 b c Strong homeostatic defense Lower Threshold Strength of challenging agent

16. a b c Strong homeostatic defense Upper Threshold Lower Threshold Lower Threshold Theoretical proposition Loss of positive wellbeing= depression Positive wellbeing is controlled by a homeostatic process Homeostatic defeat means positive wellbeing is lost Depression is the loss of positive wellbeing The measurement of positive wellbeing should be THE measure of depression

17. Is this idea consistent with (DSM-IV) ? Symptoms of depression include the following: (a) depressed mood (such as feelings of sadness or emptiness) (b) reduced interest in activities that used to be enjoyed, sleep disturbances (either not being able to sleep well or sleeping to much) (c) loss of energy or a significant reduction in energy level (d) difficulty concentrating, holding a conversation, paying attention, or making decisions that used to be made fairly easily (e) suicidal thoughts or intentions.

18. Depression is--- (a) Loss of positive affect due to homeostatic failure • reduced interest • loss of energy (d) difficulty concentrating • suicidal thoughts These are just the consequential symptoms caused by the loss of positive affect

19. How do we establish that loss of positive wellbeing = depression? How do the measures of depression and SWB relate to each other? r ≈ .7

20. 40 35.3 35 30 26.5 25 Frequency 19.1 20 4.4% 15 10 7.4 7.3 5 2.8 1.1 0.4 0.1 0 0 0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100 Percentage points of SWB How do the distributions of population incidence match? Incidence of depression in Australia

21. 79.7 80 77.7 76.0 74.4 75 72.0 71.0 70.9 PWI 70 65 65.0 63.3 Normal Mild Moderate 60 0 1-2 3-4 5-6 7-8 9-10 11-12 13-14 15-16 Depression scores (DASS) The relationship between SWB and depression (symptoms) follows the theoretical pattern prescribed by homeostasis.

22. Conclusions • 11-point end-defined scales are superior to Likert scales • (b) Depression should be defined, and measured, as a loss of positive affect.