equation we mapped the EQ-5D+ scores as reported by each
patient in our survey (Phanthunane et al., 2008) into disability
weights. We then computed the average disability weights by age
and sex. The disability weight provides a value on a cardinal scale,
with a value of 1 equal to death and 0 equal to perfect health.
2.3. Statistical analysis
The variables of interest were examined to see if they were
normally distributed. The BPRS scores and disability weights
required a log transformation to normalize them before testing
their correlation using the Pearson correlation test. A hierarchical
multiple regression analysis was used to develop a specific model
to identify the significant demographic, clinical and psychotic
symptom (i.e. positive, negative, depressive and cognitive measures)
predictors of disability weights. A hierarchical multiple
regression model allows us to quantify the impact of disease
severity on disability weights when demographic factors are
controlled. Non-parametric bootstrapping was used to produce
confidence intervals. The key statistical analyses were undertaken
using Stata 10.0 (StataCorp, Texas, USA).
3. Results
A total of 307 patients with schizophrenia were recruited and
contributed to the analyses. Table 1 presents the demographic and
clinical characteristics of survey participants. The majority of
participants were middle-aged; male; of low socioeconomic
status; poorly educated; unemployed; and never married. Few
lived independently. The average disease duration was 10 years.
The mean BPRS-E score was 39 out of 168 and the mean CGI-SCH
score was 11 out of 35. In terms of patient-based assessment, the
average DW predicted from EQ-5D+ was 0.31. While the clinicianrated
BPRS-E (median 35; 95%CI 33–37) and CGI-SCH (median 11;
95%CI 10–12) showed little spread, the patient-rated EQ-5D+
demonstrated a wider range of DW values (median 0.34; 95%CI
0.29–0.40). The median DW value of 0.34 in our sample of people
with schizophrenia under treatment is similar to the Global Burden
of Disease’s disability weight (0.351) used for treating patients
with schizophrenia (Murray and Lopez, 1996).
The severity of schizophrenia using the BPRS-E scale lies between
24 and 134 (Fig. 2a). A positive skewed distributionwas found with
60%of patients scoring less than39.Wefounda similar pattern in the
disability weights (Fig. 2b). Approximately 20% of patients reported
no problem in all six health state domains assessed. A majority of
patients (78%) had a disability weight less than 0.5.
Both clinician-rated measures, BPRS-E and CGI-SCH, as
expected, were highly correlated (0.89; 95%CI 0.87–0.91). Correlation
between disability weights and the total BPRS-E (0.47; 95%CI
0.39–0.54) and CGI-SCH (0.52; 95%CI 0.44–0.60) scores was
moderate and correlation with each of the subscales of BPRS
was modest (see Table 2).