Current evidence about MIDs for HADS

The Minimally important difference (MID) can be defined as  “the smallest difference in score in the domain of interest that patients perceive as important, either beneficial or harmful, and which would lead the clinician to consider a change in the patient’s management”⁴

King (2011)⁶ summarises the definitions, terms and methods for calculating MIDs.  For more information about MIDs in general, please read the QOL Office Frequently Asked Question “what is a minimally important difference or MID?”

The Hospital Anxiety and Depression Scale (HADS) was developed for screening purposes to identify patients with clinically significant anxiety and depression. Therefore, the HADS is typically used in clinical trials to compare prevalence rates across groups or over time. The scale can also be used as a valid measure of severity of mood disorder¹⁴, and therefore is suitable for repeated administration to assess change in patients over time. A clinically significant change in HADS has been defined as scoring below the clinical cut-off post-treatment⁵, and various HADS clinical cut-off scores have been determined for different cancer treatment studies (see Ziegler 2011 for a summary)¹³. Only a few papers have determined a MID that would indicate a clinically significant change independent of cut-off scores, however calculating and reporting the MID in clinical trials could provide valuable information. For example, an improvement in mood such that a patient is ‘no longer having suicidal thoughts’, may not register a post-treatment HADS score below the clinical cut-off but would be considered a clinically important change.  

We reviewed 210 papers reporting clinically important differences in HADS scores and found 7 papers that calculated MIDs for the HADS. The two approaches used for determining MIDs are anchor-based and distribution-based approaches. One of the papers used both anchor- and distribution-based methods with the intention of comparing and confirming results. All papers calculated effect size and used Cohen’s criteria to determine their MID. In general, effect sizes of 0.2 and 0.8 are considered small and large respectively³, while 0.5 represents a moderate effect size corresponding to a minimally important difference⁷. Table 1 summarises the target population and methods these papers used to determine MIDs for HADS.

Table 1 The populations assessed and methods used in 7 papers determining MIDs for HADS

References:

1.            Arvidsdotter, T., Marklund, B.  and Taft, C. 2013. Effects of an integrative treatment, therapeutic acupuncture and conventional treatment in alleviating psychological distress in primary care patients - a pragmatic randomized controlled trial. BMC Complementary and Alternative Medicine 13 (no pagination)(308).

2.            Bernhard, J., Sullivan, M., Hurny, C. et al. 2001. Clinical relevance of single item quality of life indicators in cancer clinical trials. British Journal of Cancer 84(9) 1156-1165.

3.            Cohen, J. 1969. Statistical power analysis for the behavioral sciences. New York: Academic Press.

4.            Guyatt, G.H., Osoba, D., Wu, A.W. et al. 2002. Methods to explain the clinical significance of health status measures. Mayo Clin Proc 77(4) 371-383.

5.            Jacobson, N.S.  and Truax, P. 1991. Clinical significance: a statistical approach to defining meaningful change in psychotherapy research. J Consult Clin Psychol 59(1) 12-19.

6.            King, M. 2011. A point of minimal important difference (MID): a critique of terminology and methods. Expert Review of Pharmacoeconomics & Outcomes Research 11(2) 171-184.

7.            Norman, G., Sloan, J.  and Wyrwich, W. 2003. Interpretation of changes in health-related quality of life: the remarkable universality of half a standard deviation. . Med Care 41(5) 582-592.

8.            Perez-San-Gregorio, M., Fernandez-Jimenez, E., Martin-Rodriguez, A. et al. 2013. Quality of life in women following various surgeries of body manipulation: Organ transplantation, mastectomy, and breast reconstruction. Journal of Clinical Psychology in Medical Settings 20(3) 373-382.

9.            Puhan, M.A., Frey, M., Buchi, S. et al. 2008. The minimal important difference of the hospital anxiety and depression scale in patients with chronic obstructive pulmonary disease. Health and Quality of Life Outcomes 6 (no pagination)(46).

10.          Svindseth, M.F., Nottestad, J.A.  and Dahl, A.A. 2010. A study of outcome in patients treated at a psychiatric emergency unit. Nordic Journal of Psychiatry 64(6) 363-371.

11.          van der Zanden, R., Kramer, J., Gerrits, R. et al. 2012. Effectiveness of an online group course for depression in adolescents and young adults: a randomized trial. Journal of Medical Internet Research 14(3) e86.

12.          Van Straten, A., Cuijpers, P.  and Smits, N. 2008. Effectiveness of a web-based self-help intervention for symptoms of depression, anxiety, and stress: Randomized controlled trial. Journal of Medical Internet Research 10 (1) (no pagination)(e7).

13.          Ziegler, L., Hill, K., Neilly, L. et al. 2011. Identifying psychological distress at key stages of the cancer illness trajectory: A systematic review of validated self-report measures. Journal of Pain and Symptom Management 41(3) 619-636.

14.          Zigmond, A.S.  and Snaith, R.P. 1983. The Hospital Anxiety and Depression Scale. Acta Psychiatrica Scandinavica 67(6) 361-370.