The use of the Short Form -36 questionnaire for older adults - SF

Age and Ageing, Nov, 1998 by Monts Ferrer, Jordi Alonso

SIR--The low completion rates for the SF-36 questionnaire in older adults seen in recent studies [1-3] have caused concern about its suitability for this age group, as pointed out in a recent editorial [4].

Hayes et al. [1] reported that 26% of their patients in a study with the anglicised version of the SF-36 had missing item data. The authors found that missing item information was higher in those aged 75 and over. O'Mahony et al. [3] also described poor completion rates for a postal administration of the SF-36 in stroke patients aged 45 years or over, but unfortunately did not report completion rates by age groups.

Missing information is a relevant issue when selecting the most appropriate questionnaire in a research project. Because the SF-36 has very good measurement properties (in all age groups) and reference values are available, we believe that before rejecting the questionnaire or modifying its content, strategies to decrease the missing data should be considered.

In the pilot test of a study using the Spanish version of the SF-36 in outpatients with chronic obstructive pulmonary disease (COPD) [5], we identified some difficulties in responding to the original `grid' format of the questionnaire, particularly among older patients. Since this was consistent with previous reports of higher missing response rates for items in `grid' format than for items printed independently (i.e. in a question and answer format) [6], we decided to use the SF-36 health survey without a `grid' format, individually typing each SF-36 question (in large print) followed by the complete response options. Additionally, we instructed interviewers to check the completeness of self-completed questionnaires, identifying (and pointing out to the patient) any missing item responses.

Out of 321 male COPD patients included in the study, more than half were 65 or over: 131 (41%) were 65-74 years and 49 (15%) were 75 or over. Seventy-three percent of the patients self-completed the questionnaire and only 5% had missed one or more items. This proportion is considerably lower than that reported by Hayes et al. [1], even though the two studies had very similar proportions of self-administered questionnaires (78% in the latter). We did not find a significant difference in missing item data among subjects younger and older than 75 years (4 vs 8%, P= 0.1). Moreover, the proportion of missing information was reduced to less than 2% of the patients when we applied the imputation algorithm recommended by the developers of the questionnaire [7].

Historically, Spanish older adults have not had much opportunity to become familiar with printed questionnaires or with `grid'-format questions. Although we ignore the relative contribution of the change in the format (`question and answer' vs `grid') and the instructions to the interviewers, we believe that both contributed to the value of the SF-36 for our patients. Simple strategies such as these (that do not change the content of the questionnaire and therefore do not compromise comparability of results) are effective and make it possible to use a robust health status measure in older adults.

MONTS FERRER, JORDI ALONSO
Health Services Research Unit
Institut Municipal d'investigacio Medica (IMIM)
C/ Doctor Aiguader, 80; E-08003 Barcelona, Spain

[1.] Hayes V, Morris J, Wolfe C, Morgan M. The 5F-36 health survey questionnaire: is it suitable for use with older adults? Age Ageing 1995; 24: 120-5.

[2.] Parker SG, Peet SM, Jagger C et al. Measuring health status in older patients. The SF-36 in practice. Age Ageing 1998; 27: 13-8.

[3.] O'Mahony PG, Rodgers H, Thomson RG et al. Is the SF-36 suitable for assessing health status of older stroke patients? Age Ageing 1998; 27: 19-22.

[4.] Gladman JRF. Assessing health status with the SF-36 (Editorial). Age Ageing 1998; 27: 3.

[5.] Ferrer M, Alonso J, Morera J et al. Chronic obstructive pulmonary disease stage and health-related quality of life. Ann Intern Med 1997; 127: 1072-9.

[6.] Ware JE, Keller SD, Gandek B et al. Evaluating translations of health status questionnaires. Methods from the IQOLA Project. Int J Technol Assessment Health Care 1995; 11: 225-51.

[7.] Ware JE, Snow KK, Keller SD, Kosinski M, Gandek B. SF-36 Health Survey. Manual and interpretation guide. Boston: The Health Institute, New England Medical Center; 1993.

SIR--The role of the SF-36 questionnaire in the assessment of health status in older people is coming under much closer scrutiny, and the work of Parker et al. [1] contributes to this. While it is increasingly clear that self-completion rates for the SF-36 decline with age (depending on the population under study), its use as an interview-based measure is also called into question by this paper. Although cautious in their criticism, the authors conclude that the interview-based approach produced completion rates which were "still unacceptable in one-quarter of the patients". In fact, this referred to the completion rate for one domain, mental health, while all the other items had completion rates of 85% or more (there being no global score for the SF-36), which would appear rather good, given the nature of the patients under study.