presents a demographic and clinical description of the general population and depression groups. Reflecting the epidemiology of depression, the percent of females in the depression groups was greater than the general population group (χ2=27.1, p<.001). Increasing depression severity was also associated with a lower percentage of being married or living together compared with the general population sample (χ2=9.3, p=.03).
As expected, depression severity and number of depression episodes were greater in the groups with current depression than the general population group. The group with depression history but no current depression was constrained to have PHQ-9 scores <5, resulting in this group having a lower depression score than the general population sample (p=.02). We did not stratify the general population sample by depression severity and seven subjects (7.4 percent) in the general population sample had PHQ-9 scores of 15 or greater, indicating moderate to severe depression. Depression chronicity (p<.001) and history of current (p<.001) or any (p<.001) depression treatment increased with depression severity. Physical health comorbidity also increased with greater depression severity with the general population reporting significantly less physical health comorbidity than all other groups.
reports the preference scores associated with the three depression health states. The overall trend was for a decrease in preference scores as the depression severity of the respondent increased. The comparisons reported here are between the general population and the other groups because the general population is the recommended source for health state preferences.
Using the SF-12 health states (), we found significant differences between the general population and moderate to severe depression groups. More specifically, for all SF-12 depression health states (mild, moderate, and severe), the general population rating scale scores were significantly higher than the moderate to severe depression group scores (89.5 versus 83.6, p=.04; 72.2 versus 62.7, p=.001; 50.7 versus 42.3, p=.02, respectively). In addition, the mean sample standard gamble scores for the mild and moderate SF-12 depression health states were significantly higher in the general population group than the moderate to severe depression group scores (0.87 versus 0.79, p=.02 and 0.77 versus 0.69, p=.01, respectively).
Using PHQ-9 health states (), five out of six general population rating scale scores were significantly higher than patient groups with current depression. The proportionate differences between the general population and patient groups with current depression also appeared to increase with hypothetical depression health state severity. For example, the proportionate differences between the severe depression group and the general population group increased from 10 percent (67.2/74.7) for the mild PHQ-9 health state to 21 percent (49.5/62.6) for the moderate PHQ-9 health state to 29 percent (30.7/43.5) for the severe PHQ-9 health state. No significant differences were found between the general population group and the depression history only group except for a trend for the severe hypothetical depression health state (43.5 versus 35.8, p=.05). Standard gamble comparisons resulted in more limited differences. The mean general population standard gamble scores for the mild and moderate PHQ-9 depression health states were significantly higher than the mean moderate to severe depression group scores (0.78 versus 0.70, p=.03 and 0.70 versus 0.63, p=.03, respectively).
As expected, patients with current depression rated their current health lower than the general population using the rating scale and standard gamble (see ). For example, the general population rating scale score for current health was significantly higher than the mild to moderate and moderate to severe depression groups (85.2 versus 71.0, p<.001 and 85.2 versus 49.0, p<.001, respectively), and the general population standard gamble scores were also significantly higher than the mild to moderate and moderate to severe depression groups (0.83 versus 0.74, p=.02 and 0.83 versus 0.60, p<.001, respectively). However, when subjects were asked to rate their current health without taking into account the effects of depression there were no significant differences between the general population and depression group scores. There was a significant difference between the general population and the depression history only group standard gamble score for current health without taking into account the effects of depression (0.86 versus 0.94, p=.049, respectively).
Test–retest preference score results for the hypothetical depression health states were obtained from 15 general population subjects and 34 patient subjects. The intraclass correlation coefficient for all subjects completing the test–retest procedure was in the fair to good range: 0.519 for visual analog scale (VAS) and 0.522 for standard gamble (SG) scores (Fleiss 1986
). We examined the mean rank difference for each group across the 12 different hypothetical depression health states using a nonparametric Mann–Whitney U
test and found no statistical differences between the general population and patient groups. The absolute difference of mean differences for the VAS scores ranged from 0.18 to 3.80 using the 1–100 scale and from 0.01 to 0.04 for the SG scores using the 0–1 scale.