Development and Validation of the Mini-Osteoporosis Quality of Life ...

Osteoporos Int (1999) 10:207–213 ß 1999 International Osteoporosis Foundation and National Osteoporosis Foundation

Osteoporosis International

Original Article Development and Validation of the Mini-Osteoporosis Quality of Life Questionnaire (OQLQ) in Osteoporotic Women with Back Pain due to Vertebral Fractures. Osteoporosis Quality of Life Study Group* *Protocol development: D. J. Cook1,2, G. H. Guyatt1,2, J. D. Adachi1, R. S. Epstein3, E. F. Juniper2; Clinical protocol development and data collection: Hamilton, Ontario: P. A. Austin2, J. Clifton2, J. D. Adachi; Bangor, Maine: C. J. Rosen4, C. R. Kessenich5; Worcester, Massachusetts: J. L. Stock6, J. Overdorf6; Denver, Colorado: P. D. Miller7, A. L. Erickson7; Portland, Oregon: M. R. McCLung8, B. L. McClung8; Data analysis and interpretation:L. E. Griffith2, G. H. Guyatt, D. J. Cook; Manuscript preparation: G. Ioannidis1, J. D. Adachi, G. H. Guyatt 1 Department of Medicine, St Joseph’s Hospital, McMaster University, Hamilton, Ontario Canada; 2Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada; 3Merck-Medco Managed Care Inc., Montvale, New Jersey, USA; 4Department of Medicine, St Joseph’s Hospital, Bangor, Maine, USA; 5Faculty of Nursing, Husson College, Bangor, Maine, USA; 6Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA; 7 Department of Medicine, University of Colorado, Denver, Colorado, USA; 8Department of Medicine, Oregon Osteoporosis Center, Portland, Oregon, USA

Abstract. The objective of the study was to evaluate a shortened osteoporosis quality of life questionnaire (OQLQ) in osteoporotic women with back pain due to vertebral fractures. From the longer 30-item OQLQ (four to nine items per domain) we created the mini-OQLQ by choosing the two items with the highest impact in each of five domains (symptoms, physical function, activities of daily living, emotional function, leisure). We administered the OQLQ, the Sickness Impact Profile, the SF-36 and the Brief Pain Index to patients at baseline, after 2 weeks and after 6 months. The intraclass correlations between baseline and the 2-week follow-up for the five mini-OQLQ domains ranged from 0.72 to 0.86. Cross-sectional correlations between the domains of the mini-OQLQ and other health instruments were moderate to large (0.35–0.80) and greater than predicted. The mini-OQLQ items showed moderate to large correlations with items omitted from the shortened questionnaire (0.44–0.88). Correlations between the

Correspondence and offprint requests to: Dr Jonathan D. Adachi, 25 Charlton Avenue E., Suite 501, Hamilton, Ontario, Canada, L8N 1Y2.

OQLQ domains and the other three instruments were greater than those of the mini-OQLQ, and partial correlations between OQLQ items omitted from the mini-OQLQ and the other three instruments after considering mini-OQLQ items were substantial (0.19– 0.71) and statistically significant. Sample sizes of less than 200 per group should be required to detect minimally important differences in parallel-group clinical trials. Longitudinal correlations between the miniOQLQ and the other measures were often significant but generally lower than predicted (0.10–0.49). The partial correlations revealed that the omitted items explained a significant portion of the longitudinal variance in each domain. We conclude that in a selected group of patients with back pain caused by vertebral fractures, the miniOQLQ demonstrated good discriminative and adequate evaluative properties. The mini-questionnaire should be useful in clinical settings.

Keywords: Clinical settings; Osteoporosis; Quality of life; Shortened questionnaire; Vertebral fractures

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Introduction The most common symptom of osteoporosis is back pain resulting from vertebral fractures. Back pain may be crippling and has a major impact on a patient’s ability to perform activities of daily living. Patients with chronic back pain are usually unable to work [1], are limited in their social and recreational activities [2] and are emotionally distressed [3,4]. While clinicians and investigators may utilize a variety of questionnaires to assess their patients’ health-related quality of life (HRQL) [5–7], their length and the time they take to complete may limit their use [8,9]. Demands for efficiency and the promise of decreased respondent burden, greater compliance, and clinical feasibility have led to the development of shorter questionnaires [10–12]. We have previously developed a disease-specific instrument, the Osteoporosis Quality of Life Questionnaire (OQLQ ) [7], that measures HRQL for osteoporotic women with back pain due to vertebral fractures. The OQLQ proved reliable and valid for measuring both differences in HRQL between patients with osteoporosis and changes within these patients over time. Moreover, in women with one or more vertebral fracture, the OQLQ has been found to have psycometric properties slightly superior to the Quality of Life Questionnaire of the European Foundation for Osteoporosis [13,14]. To enhance the usefulness of the OQLQ in clinical practice and large-scale randomized trials, we have developed a shortened version of the instrument, the mini-OQLQ. The objectives of this study were to test the performance of the mini-OQLQ and to compare its results with those of the original instrument.

Methods Patients and Questionnaire Development Details about patient recruitment have been reported elsewhere [7]. Briefly, we enrolled from one secondary care rheumatology practice in Canada and four American metabolic bone disease practices women who were over the age of 50 years, whose last menstrual period was at least 1 year prior to enrollment and who had a clinical diagnosis of sudden-onset back pain following osteoporosis-induced fractures and at least one vertebral fracture (defined as a 15% reduction in anterior height relative to posterior height). We excluded patients with any difficulties that would prevent reliable completion of the questionnaire, and those with secondary causes of bone loss or any additional medical conditions or illnesses other than osteoporosis that might explain their pain or influence their HRQL. A total of 227 patients met the entry criteria: 118 patients from the Canadian site and 109 patients from the four American sites. The findings of a previous study formed the basis of the OQLQ and the mini-OQLQ [15]. In this cross-

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sectional survey study, we asked 100 osteoporotic women to comment on the extent to which they were troubled by 168 health-related problems. We calculated an impact score for each item by multiplying the number of times an item was identified as being a problem by its mean importance (scale of 1–5: ‘1, not at all important’ to ‘5, very important’). From this early study, we chose the items with the highest impact to create the 30-item OQLQ that includes nine items related to symptoms, five to physical function, eight to activities of daily living, four to emotional function and four to leisure activities [7]. Each item is associated with a 7-point scale in which a rating of 7 represents the best possible function and a rating of 1 represents the worst possible function. The mini-OQLQ includes the top two items in each of the five domains (Appendix). To determine the usefulness of the mini-OQLQ, we re-analyzed the data collected from the original questionnaire for only the 10 items of the mini-OQLQ.

Instrument Testing We examined both the ability of the mini-OQLQ to differentiate between patients according to their HRQL (its discriminative properties – reliability and crosssectional validity) and its ability to measure changes in HRQL over time (its evaluative properties – responsiveness and longitudinal validity) [16]. As we described elsewhere [7], patients completed the OQLQ and three other questionnaires at baseline, after 2 weeks and after 6 months. The other questionnaires were as follows: 1. The Sickness Impact Profile (SIP) is a generic health status instrument that has 136 statements in a yes–no format that is divided into 12 categories [17]. The instrument takes 15–35 min to complete. 2. The Medical Outcomes Survey (SF-36) Instrument is a generic instrument that measures HRQL and has 36 multiple-choice questions divided into eight subscales [18]. The instrument takes approximately 8–10 min to complete. 3. The Brief Pain Index (BPI) is a problem-specific severity scale comprised of four questions regarding a patient’s pain. These questions include a patient’s worst pain, least pain and average pain in the last 24 h; and a patient’s pain at present [19]. The Index takes less than 2 min to complete.

Statistical Analysis Discriminative Properties. We assessed the reliability of the mini-OQLQ using the intraclass correlation coefficients from baseline to the follow-up visit at 2 weeks. Pearson correlation coefficients on the mean scores across the three visits were used to calculate crosssectional construct validity between the domains of the mini-OQLQ and the three other instruments. We made a priori predictions of the magnitude of the correlations and compared our results with those expected.

Development and Validation of the Mini-Osteoporosis Quality of Life Questionnaire

To explore the relation between the OQLQ and the mini-OQLQ we calculated Pearson correlation coefficients in each OQLQ domain between the mini-OQLQ items and those items not included in the mini-OQLQ. In addition, we calculated partial Pearson correlation coefficients between items omitted in the shortened OQLQ with the three other instruments after considering mini-OQLQ items. The extent of the correlation would help determine the capability of the omitted items to explain the variance associated with the SIP, the SF-36 and the BPI. Evaluative Properties. The more responsive an instrument, the smaller the sample size required to detect a change in quality of life. To estimate responsiveness we calculated the sample size needed to detect a mean difference due to treatment, equivalent to a small but important difference in an individual patient’s HRQL. From previous work we have found that the minimal, clinically important difference for an HRQL instrument using 7-point scale response options is 0.5 per question [20]. On the basis of this assumption and the standard deviation of the differences in study participants, and assuming a two-sided type I error of 0.05 and a beta error of 0.1, we calculated sample size requirements for both the mini-OQLQ and the OQLQ. To explore longitudinal construct validity, we calculated Pearson correlation coefficients for the changes during adjacent visits between the domains of the mini-OQLQ and the SIP, SF-36 and BPI. Patients with complete data provided two data points for each correlation (the difference between baseline and the 2-week follow-up and the difference between the follow-up at 2 weeks and 6 months). We made a priori predictions of the magnitude of the correlations and compared our results with those expected. We took a similar approach as in discriminative validity to explore the relation between the original OQLQ and the mini-OQLQ: calculating correlations between mini-OQLQ and the remaining items, and calculating partial correlations with remaining items and the independent measures after taking into account miniOQLQ items. For longitudinal validity, however, we used change scores between baseline and 2 weeks, and between the 2-week and 6-month follow-up visits.

Results Patients As previously described [7], patient baseline characteristics in the United States and Canada were very similar; the patient population was therefore pooled (Table 1). Of the 226 patients enrolled in the study, 26 withdrew from the study, for a variety of reasons, before completing all three scheduled visits.

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Table 1. Demographic baseline information Variable

Characteristics of the women (n = 226)

Age (years)a Duration of osteoporosis (years)a,b Lumbar spine bone density (g/cm2)a No. of fracturesa Total Lumbar Thoracic Lives alone (%) Requires help dressing Requires help bathing Requires help shopping Requires help housekeeping Sickness Impact Profilea Physical Psycho-social Medical Outcomes Surveya Well-being Functional status

69.6 ± 7.4 4.7 ± 3.9 0.84 ± 0.14 2.78 ± 2.04 0.83 ± 1.04 1.95 ± 1.71 33.2% 3.1% 5.8% 23.6% 37.3% 6.27 ± 7.29 5.56 ± 7.26 61.75 ± 16.15 57.77 ± 22.90

a

.Values are mean ± standard deviation. .Duration from first documented vertebral fracture associated with pain until questionnaire administration. b

Discriminative Properties The intraclass correlations for the five domains were as follows: emotions 0.77, symptoms 0.81, physical function 0.80, activities of daily living 0.74, leisure 0.76. Table 2 summarizes predicted and observed Pearson correlation coefficients between the miniOQLQ and the other instruments. Missing entries in the table represent relations for which we made no a priori predictions. In all but two instances, the correlations were higher than anticipated. The correlations between the original questionnaire and the three other instruments (data not shown) were consistently higher than the correlations between the mini-OQLQ and the SIP, SF-36 and BPI. The correlations between the mini-OQLQ items and those omitted from the shorter instrument were as follows: emotions 0.44, symptoms 0.88, physical function 0.78, activities of daily living 0.81, leisure 0.57. Table 3 displays the partial correlations between the other instrument and the OQLQ items not included in the mini-OQLQ after taking mini-OQLQ items into account. The partial correlations demonstrate that the omitted items explained a significant portion of the cross-sectional variance associated with the SIP, SF-36 and BPI.

Evaluative Properties Table 4 presents the sample size needed to detect a mean difference equivalent to the minimally important difference in the five domains of the mini-OQLQ and compares these results with the original OQLQ. Sample

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Table 2. Pearson correlation coefficients for cross-sectional construct validity between the mini-OQLQ and the other quality of life instruments measuring pain and physical and emotional function Domain

BPI

SIP

SF-36

Physical Emotions Symptoms Physical function Activities of daily living Leisure

0.80 (>0.5) 0.66 (>0.3)

psycho-social

Mental health

0.35 (>0.4)

0.38 (>0.4)

0.54 (>0.3) 0.56 (>0.5) 0.49 (>0.4)

Physical

0.74 (>0.5) 0.69 (>0.25) 0.66 (>0.25)

0.47 (>0.25)

BPI, Brief Pain Index; SIP, Sickness Impact Profile; SF-36, Medical Outcomes Survey; the numbers in parentheses are the predicted correlations. All correlations are significant (p0.3)

(0.25 (>0.40) (0.24 (>0.25) (0.19 (>0.25)

Activities of daily living Leisure

BPI, Brief Pain Index; SIP, Sickness Impact Profile; SF-36, Medical Outcomes Survey; the numbers in parentheses are the predicted correlations. Correlations 50.19 are significant (p0.05).

Table 6. Partial longitudinal correlations for each domain between the OQLQ items not included in the mini-OQLQ and the other quality of life instruments after accounting for mini-OQLQ items Domain

BPI

SF-36 Mental health

Emotions Symptoms Physical function Activities of daily living Leisure

Physical

0.28 0.17 0.22

0.28 0.30 0.41

BPI, Brief Pain Index; SIP, Sickness Impact Profile; SF-36, Medical Outcomes Survey. All correlations are significant (p