Epidemiology/Health Services/Psychosocial Research ORIGINAL ARTICLE Development and Factor Analysis of a Questionnaire to Measure Patient Satisfaction With Injected and Inhaled Insulin for Type 1 Diabetes JOSEPH C. CAPPELLERI, PHD, MPH IONE A. KOURIDES, MD system that permits noninvasive delivery of ROBERT A. GERBER, PHARMD, MA ROBERT A. GELFAND, MD rapid-acting insulin was developed (Inhale Therapeutics Systems, San Carlos, CA) that offers an effective and well-tolerated alternative to preprandial insulin injections in type 1 diabetes (3). Inhaled insulin, OBJECTIVE — To develop a self-administered questionnaire to address alternative deliv- intended for use in a preprandial therapeu- ery routes of insulin and to investigate aspects of patient satisfaction that may be useful for tic regimen, is the first practical alternative subsequent assessment and comparison of an inhaled insulin regimen and a subcutaneous to injections for therapeutic administration insulin regimen. of insulin. However, measures of treatment RESEARCH DESIGN AND METHODS — Attributes of patient treatment satisfaction satisfaction in diabetes have not directly with both inhaled and injected insulin therapy were derived from five qualitative research stud- examined delivery routes for insulin other ies to arrive at a 15-item questionnaire. Each item was analyzed on a five-point Likert scale so than by injection (e.g., syringe, pen, or that higher item scores indicated a more favorable attitude. There were 69 subjects with type 1 pump) and were developed at a time when diabetes previously taking injected insulin therapy who were enrolled in a phase II clinical trial. only injectable forms of insulin were readily Their baseline responses on the questionnaire were evaluated and subjected to an exploratory available in clinical practice (4–7). There- factor analysis. Meaningful factors were retained and interpreted based on their psychometric fore, patient satisfaction with inhalation properties. delivery of insulin needs to be investigated. This article reports the development of RESULTS — Exploratory factor analysis suggested a two-factor solution accounting for 66 a self-administered questionnaire whose and 20% of the variance, respectively. The first factor contained 10 reliable items (Cronbach’s ␣ = 0.89) relating to convenience and ease of use, and the second contained 5 reliable items items are tailored to novel as well as exist- (Cronbach’s ␣ = 0.82) relating to social comfort. ing forms of insulin delivery. As a first step to explore and identify attributes of patient CONCLUSIONS — Among patients with type 1 diabetes, this analysis highlighted and satisfaction in this context, we undertook a quantified two key factors contributing to patient satisfaction: convenience/ease of use and factor analysis on baseline responses of the social comfort. The questionnaire underwent rigorous development, had reliable properties, questionnaire. Such an analysis can serve as and an interpretable and rich factor structure. This report is intended to help advance, in sub- a conduit for subsequent research in the sequent investigations, the understanding and measurement of treatment satisfaction with assessment and comparison of patient sat- novel and existing forms of insulin delivery. isfaction with, for example, inhaled insulin therapy and subcutaneous insulin therapy. Diabetes Care 23:1799–1803, 2000 RESEARCH DESIGN AND he Diabetes Control and Complications One limitation may be the inconvenience METHODS Trial (1) and the Stockholm Diabetes and poor patient acceptability of a program TIntervention Study (2) have demon- of multiple daily insulin injections. Patient satisfaction questionnaire strated the benefits and impact of good The search for a practical alternative to Attributes of patient satisfaction with treat- glycemic control in type 1 diabetes. How- injections for therapeutic administration ment for both injectable and inhaled ever, despite the results of these studies, of insulin is nearly as old as the discovery insulin therapy were derived from five intensive insulin therapy has been slow to of insulin itself. Recently, a novel dry powder qualitative research studies that consisted of gain acceptance in clinical practice settings. insulin formulation and aerosol delivery one-on-one interviews conducted in the U.S. Two studies (n = 100 and n = 41) included people with type 1 and type 2 From Pfizer Inc. (J.C.C., R.A.Ger., R.A.Gel.), Global Research and Development, Groton, Connecticut; and Pfizer Inc. (I.A.K.), New York, New York. (insulin-using) diabetes; one study (n = 44) Address correspondence and reprint requests to Joseph C. Cappelleri, PhD, MPH, Pfizer Inc., M.S. 8260- included people with type 1 and type 2 253, Eastern Point Road, Groton, CT 06340. Email: [email protected]. (insulin-using and non–insulin using) dia- Received for publication 13 June 2000 and accepted in revised form 29 August 2000. betes; one study included 10 subjects (1 All authors are employed by and hold stock in Pfizer Inc. Abbreviations: PSIT, Patient Satisfaction with Insulin Therapy. subject with type 1 diabetes and 9 subjects A table elsewhere in this issue shows conventional and Système International (SI) units and conversion without diabetes) who used the inhaler factors for many substances. system four times a day (placebo, no med- DIABETES CARE, VOLUME 23, NUMBER 12, DECEMBER 2000 1799 Factor analysis of the PSIT Table 1—Baseline clinical characteristics of type 1 diabetes recruited into a 12-week Step 2 involved a promax (oblique) the study population parallel study of an inhaled insulin regimen rotation on the retained factors to help with versus a conventional subcutaneously interpretation. An oblique rotation was injected insulin regimen conducted at 10 applied because it was hypothesized (and n 69 centers in the U.S. Subjects completed the later confirmed) that the factors would be Sex (M/F) 37/32 baseline questionnaire in ϳ5–10 min. The correlated with one another. Step 3 Age (years) 37.4 ± 9.0 (18.0–56.0) design and clinical results of this study involved interpreting the rotated solution Duration of diabetes 14.6 ± 9.3 (1.2–35.0) have been reported elsewhere (3). by identifying which items load on each (years) Subjects were aged 18–56 years and on retained factor, the conceptual meaning of Race/ethnic group a stable insulin administration schedule (for at items that load on the same factor, and White 55 (80) least 2 months) involving two to three pre- conceptual differences in items that load on Black 2 (3) scribed insulin injections daily. Both screening different factors. Pattern loadings near 0.40 Hispanic, other 12 (17) and prerandomization HbA values were or greater (in absolute value) were used to Weight (kg) 1c between 7.0 and 11.9%, with fasting plasma interpret the results (9,11). Men 81.3 ± 10.8 (56.3–103.6) C-peptide Յ0.2 pmol/ml. All had body Women 64.1 ± 7.5 (50.2–76.7) weight of 80–130% of ideal (Metropolitan Internal consistency and stability BMI (kg/m2) Life Insurance Tables). Subjects were non- Cronbach’s ␣ reliability coefficient (12) was Men 25.5 ± 2.7 (21.0–31.0) smokers (for at least 6 months) and had a computed for each factor (domain) and total Women 24.4 ± 2.8 (19.0–31.0) normal chest X-ray, normal pulmonary func- scale to measure internal consistency. An HbA (%) 8.5 ± 1.1 (6.4–11.2) 1c tion test results, and an electrocardiogram item-total correlation between an individual Data are n, means ± SD (range), or n (%). A total of with normal sinus rhythm at a rate of 50–100 item and the sum of the remaining items on 73 men and women with type 1 diabetes were enrolled. One subject was discontinued before ran- beats/min. All subjects performed home a factor or total scale was calculated to fur- domization, and complete data were not available. Of blood glucose monitoring four times daily. ther assess reliability. the remaining 72 subjects, there were no discernible Baseline responses from a total of 69 subjects A second baseline measurement was differences between the 3 subjects excluded and the were considered in the factor analysis. not available for baseline test-retest reliabil- 69 subjects included (3). ity (stability). However, Pearson correlations Factor analysis between baseline (“test”) and posttreatment To further understand and identify attrib- (“retest”) scores at 12 weeks were measured ication of any kind was given) for 14 days utes of patient satisfaction, we conducted among patients who continued with, and and maintained a daily diary; and one an exploratory factor analysis of the base- were randomized to, traditionally adminis- study (n = 10) included health care profes- line questionnaire responses. Factor analy- tered subcutaneous insulin. Statistical sig- sionals (2 primary care physicians, 2 sis is a statistical technique that reduces a nificance was based on P Ͻ 0.05. internists, 2 endocrinologists, 2 pharma- large number of interrelated questions to a cists, and 2 certified diabetes educators). smaller number of underlying common Relationship of satisfaction scores Based on these studies, items and con- factors or domains that are primarily with demographic and medical tent relating to patient satisfaction with responsible for covariation in the data (8). variables insulin treatment were identified. The initial We followed a standard approach to We examined the relationship of satisfaction item pool was further reduced to contain conducting an exploratory factor analysis scores with the demographic and medical only items that were clear and not redun- (8,9). Three major sequential steps were variables found in Table 1. Pearson correla- dant. Emphasis was placed on using simple undertaken. Step 1 involved identifying the tion (r) was used to measure the association and unambiguous wording of items and number of meaningful factors to retain based of satisfaction scores with these variables responses. The resulting questionnaire—the on the scree test (10) and the percentage of except race, for which an analysis of vari- Patient Satisfaction with Insulin Therapy (common) variance accounted for by a given ance model was applied.