Participants were required to be (1) diagnosed with type 2 diabetes by a recognized medical professional (as indicated by patient self-report); (2) between 30 and 75 years old; (3) able to identify the age at which they were first diagnosed with diabetes; (4) able to read and understand English; and (5) willing and able to give informed consent prior to study entry. Patients were not eligible if they had cognitive impairment, hearing difficulty, or severe psychopathology that could interfere with the ability to complete the study measures. Participants were recruited through ten advertisements placed in four newspapers in Scotland and England from June to August of 2005. Interested patients responded by telephone, and 200 potential participants were screened to assess whether they met the study inclusion/exclusion criteria. Of the 200 screened patients, 132 were available, eligible, and willing to participate. Two participants who attended the interview were unable to complete the questionnaires relevant to the current analysis. Thus, the current study includes a sample of 130 individuals with type 2 diabetes.

Patients completed a brief questionnaire that included questions on age, sex, ethnicity, living situation, employment, education, diabetes-related health, and general health. Participants' weight and height were measured at the beginning of each interview and recorded on the demographic and clinical information form so that patients' Body Mass Index (BMI) could be computed 45. Items assessing diabetes-related health included questions asking whether participants had ever experienced hyperglycemia, daytime hypoglycemia, or nighttime hypoglycemia.

Data were collected in Edinburgh and London during August 2005. All procedures and instruments were approved by an independent Institutional Review Board, and all participants provided written informed consent prior to completing any study measures. After signing the consent form, participants independently completed the questionnaires analyzed in the current study.

Statistical analyses were completed using SAS version 8.12 (SAS Institute, Cary, NC). Descriptive statistics were used to summarize demographic/clinical characteristics and scores on health status measures. Categorical variables are summarized in terms of frequencies and percentages, and for each continuous variable, the mean, standard deviation, median, range, percent at floor, and percent and ceiling are presented. In the current study, there were no missing data on any of the measures, and therefore, procedures for handling missing data were not followed. Internal consistency reliability is the extent to which individual items within a scale are related to one another. Internal consistency was examined for the PGWB subscales and global score using Cronbach's formula for coefficient alpha. Cronbach's alphas greater than 0.70 are generally considered acceptable 9.

Construct validity refers to the extent to which the instrument measures what it is intended to measure. To assess the construct validity of the EQ-5D and PGWB, both convergent and known-groups validity were examined. Convergent validity is the degree to which scores from the instrument undergoing evaluation are related to scores from an instrument measuring a similar construct. To examine convergent validity, Spearman correlations were performed to examine the relationship of the two generic measures with diabetes-specific patient-reported measures and patients' BMI. BMI was used as a criterion because body weight is an important health indicator for patients with type 2 diabetes. Roughly 40% to 50% of patients with diabetes meet criteria for obesity 2646, and obesity is likely to exacerbate symptoms and metabolic abnormalities of type 2 diabetes, increase the risk of complications, and complicate the goal of achieving glycemic control 47484950. Correlation coefficients were interpreted based on guidelines proposed by Cohen 51 suggesting that a correlation of 0.10 is small, 0.30 is moderate, and 0.50 is large. It was hypothesized that the generic measures under investigation would be significantly correlated with the condition-specific measures and patients' BMI, with correlation coefficients in the moderate to large range.

Known-groups validity is a scale's ability to discriminate among groups of patients who are known to differ by a key indicator. Using t-tests, EQ-5D and PGWB scores were compared among groups of patients who differed in the following characteristics: symptom burden as reported on condition-specific measures; type of pharmacological treatment (injectable insulin vs. oral medication only); preference for weight change (patients who would like to lose weight vs. patients who would like to stay the same weight); and experience with daytime hypoglycemia, nighttime hypoglycemia, and hyperglycemia (patients who had each of these experiences vs. patients who did not). It was hypothesized that the EQ-5D and PGWB would discriminate between groups of patients in each of these comparisons.

A total of 130 eligible participants completed the study, 53 in Edinburgh and 77 in London (Table 1). The sample in London was more ethnically diverse than the sample in Edinburgh, which was 100% White. There were no other statistically significant differences between the two geographic groups with respect to demographics (e.g., gender, age, marital status, employment) or clinical characteristics (e.g., BMI, age when first diagnosed with diabetes, current treatment). Therefore, data from the two cities were pooled for all analyses.

The majority of participants were male (n = 84; 64.6%), and the mean age of the total sample was 55.7 years old. Most of the patients were currently married (n = 79; 60.8%), over a third worked full-time (n = 46; 35.4%), and over a third were retired (n = 47; 36.2%). The mean Body Mass Index (BMI) of the total sample was 31.5, which is considered to be in the obese range 45. The mean age when first diagnosed with diabetes was 49.1 years old. Most participants received oral, but not injectable medications for treatment of their diabetes (n = 85; 65.4%). A total of 31 participants (23.8%) were treated with injectable medications, either alone or in combination with oral medications.

There were no missing data on the EQ-5D (Table 2). The great majority of the 130 participants reported no problems on the EQ-5D self-care item (n = 120; 92.3%), while the other four dimension items reflected greater rates of difficulty. Roughly one third of participants reported having at least some problems in the dimensions of mobility (n = 42; 32.3%) and usual activities (n = 41; 31.5%). Approximately a third of patients reported having either some problems (n = 35; 26.9%) or extreme problems (n = 8; 6.2%) in the anxiety/depression dimension. The greatest rates of difficulty were found in the pain/discomfort dimension, with half of the sample reporting either some problems (n = 52; 40.0%) or extreme problems (n = 13; 10.0%). The pattern of responses was similar in the London and Edinburgh samples, although the participants in Edinburgh reported slightly greater rates of problems in mobility, self-care, and usual activities. The mean EQ-5D index score of 0.75 and VAS score of 68.8 both indicate a moderate level of overall impairment in this sample (Table 3). The mean index score was somewhat lower for the Edinburgh sample (0.70) than for the London sample (0.79). Analysis of floor and ceiling effects revealed that 40% of the sample had the maximum EQ-5D index score of 1. The VAS did not have a similar ceiling effect.

On the PGWB, there were no missing data, and mean subscale scores were similar in the two samples (Table 4). The greatest impairment was reflected in the vitality subscale, which had a mean score of 59.5 in the total sample of 130 participants. The positive well-being and general health subscales also reflected some impairment (mean scores of 61.1 and 63.4, respectively). Higher scores were found on the anxiety, depressed mood, and self-control subscales (69.9, 78.9, and 78.0, respectively). On the depressed mood subscale, 23.8% of the sample had the maximum score of 100, indicating that almost a quarter of this sample reported no problems with depression. The PGWB demonstrated good internal consistency reliability, with Cronbach's alphas for the six subscales ranging from 0.77 to 0.92 (Table 5). The alpha for the global score was 0.97.

Convergent validity of the EQ-5D index score and VAS were demonstrated through significant correlations with the ADS, DSC-R, and patients' BMI (Table 6). These correlations were generally in the moderate to large range. Spearman correlations of the index score and VAS with the ADS had coefficients of -0.52 and -0.49, respectively (both p < 0.001). Correlations with the DSC-R total score were -0.64 and -0.53 (both p < 0.001). Correlations between the EQ-5D and the DSC-R subscales ranged from -0.33 to -0.61 (all p < 0.001), except for the correlations with the ophthalmology subscale which were somewhat smaller (r = -0.22 and -0.19; both p < 0.05). Correlations of the EQ-5D index score and VAS with patients' BMI were -0.27 (p < 0.01) and -0.38 (p < 0.001).

Convergent validity of the PGWB global score was also supported (Table 6), with the majority of correlations in the moderate to large range. Correlations of the PGWB global score with the ADS and the DSC-R total score had coefficients of -0.61 and -0.71, respectively (both p < 0.001). Correlations of the PGWB global score with the DSC-R subscales, except the ophthalmology subscale, ranged from -0.45 to -0.76 (all p < 0.001). The correlation with patients' BMI was somewhat smaller, but still statistically significant (r = -0.24; p < 0.01).

The PGWB subscales also demonstrated good convergent validity. Correlations of these six subscales with the ADS ranged from -0.48 to -0.61 (all p < 0.001). Similarly, all PGWB subscales had correlations with the DSC-R total score that were in the large range (r = -0.57 to -0.68; all p < 0.001). Correlations between PGWB subscales and DSC-R subscales were all in the moderate to large range and statistically significant (p < 0.001), except for those involving the DSC-R ophthalmology subscale which were notably smaller. Correlations with BMI were statistically significant for four PGWB subscales: positive well-being (r = -0.19), self-control (r = -0.20), general health (r = 0.28), and vitality (r = 0.28). The anxiety and depressed mood subscales of the PGWB were not significantly correlated with BMI.

Known-groups validity of the EQ-5D index score and VAS was supported in several group comparisons (Table 7). Both EQ-5D scores significantly discriminated between groups of patients categorized based on median splits of their ADS score and DSC-R total score (all p < 0.001). Groups with higher scores (indicating greater symptom burden) on these two diabetes-specific instruments had lower EQ-5D scores (indicating lower HRQL). In addition, patients who wanted to lose weight (n = 113) had significantly lower EQ-5D scores than patients who wanted to stay the same weight (n = 16) (both p < 0.001). Patients who had experienced daytime hypoglycemia had significantly lower mean EQ-5D index (p < 0.05) and VAS (p < 0.001) scores than patients who had not experienced daytime hypoglycemia. Results followed a similar pattern for hyperglycemia and nighttime hypoglycemia, although comparisons were not consistently statistically significant.

The PGWB also discriminated between groups of patients who differed in scores on diabetes-specific instruments and clinical characteristics (Table 7). Groups with higher scores (indicating greater symptom burden) on the ADS and DSC-R total score had lower PGWB global scores (indicating lower overall well-being) (both p < 0.001). Patients who wanted to lose weight (n = 113) had a significantly lower mean PGWB global score than patients who wanted to stay the same weight (n = 16) (p < 0.05). The PGWB global score also discriminated between groups of patients differing with regard to whether they had experienced daytime hypoglycemia, nighttime hypoglycemia, and hyperglycemia (all p < 0.05). Known-groups validity of the PGWB subscales was also supported (Table 8). Statistically significant group differences were found in most comparisons involving the anxiety, positive well-being, self-control, general health, and vitality subscales. The depressed mood subscale discriminated between groups of patients determined by median splits on the ADS and DSC-R, but significant differences on this subscale were not found in the other group comparisons.

No scales of the EQ-5D or PGWB significantly discriminated between patients treated with injectable medication (i.e., insulin with or without concomitant oral medication; n = 31) and patients treated only with oral medications. In general, scores were somewhat higher in the oral treatment group, but these differences between groups were not statistically significant.