The results of this analysis demonstrate that the PHQ-9 total score functions fundamentally the same in subjects from 4 of the largest racial/ethnic groups in the United States. The similar mean scores and factor structure of the PHQ-9 in the different groups—even while the vast majority of Chinese Americans and Latinos in this analysis completed the PHQ9 in a language other than English—suggests that it can be used without adjustment in diverse populations. These findings also support the idea that the DSM-IV criteria for major depression are common to individuals of all cultures.
Mean PHQ-9 scores were similar amongst the different racial/ethnic groups. Unlike what has been seen in previous studies, Latinos in our study did not have higher mean PHQ-9 scores compared with the other racial/ethnic groups. 30, 31
Our findings imply that there is no need to adjust PHQ-9 threshold scores for depression in patients from Latino backgrounds. 32
One possible reason for this difference between our study and past research is that prior studies used measures such as the CES-D or Beck Depression Inventory that were not strictly criterion-based, unlike the PHQ-9.
Chinese Americans also did not have significantly different mean scores than individuals from other groups, but a smaller proportion of Chinese Americans had a clinically significant level of depressive symptoms as indicated by a score of 10 or higher. Gender stratification revealed much lower rates of depressive symptoms among Chinese American men while Chinese American women had rates of depression statistically indistinguishable from other racial/ethnic groups. These gender differences are consistent with prior studies 33
as well as epidemiological studies of Chinese Americans that showed acculturated Chinese American women have twice the likelihood of lifetime depressive episodes as Chinese American men. 34
Future studies could explore further this possibility that gender mediates the effect of acculturation on endorsement of depressive symptoms.
This study is the first to examine the factor structure of the PHQ-9. The fact that all 9 of these items load onto a single factor suggests that the PHQ-9 is measuring a coherent, unitary concept of major depressive disorder based on the DSM-IV criteria. Furthermore, the fact that this single factor comprising all 9 items is seen in all 4 racial/ethnic groups suggests that the core features of depression are common in these groups. Although there may be some differences in the expression of individual symptoms across racial/ethnic groups, these differences are relatively minor. In our analysis, there was consistency in the core features of depression across racial/ethnic groups, similar to what was found in past cross-national studies. 35, 36
This is illustrated by the fact that between all 4 groups there was no significant difference in mean scores of the individual item of depressed mood.
Our finding that Chinese Americans have higher rates of endorsement of psychomotor abnormalities and sleep is consistent with previous studies showing that Asian subjects are more likely to have somatic symptoms. 13, 37, 38
Conversely, we have not seen any previous literature that parallels our finding that Asian subjects had much fewer symptoms of appetite changes. Future studies of depressive symptomatology that include Chinese Americans should help to confirm or refute this finding.
Our finding that Latino subjects had a higher endorsement of anhedonia on individual item analysis shows similarities with studies of other depression screening instruments. These previous studies have found that Latinos report positive emotional states less often than non-Hispanic whites. 18, 31
Similar to our study, prior research has also shown that after controlling for sociodemographic factors there was no difference found in the endorsement of symptoms of negative affect or somatic disturbance between Latinos and non-Hispanic white populations. 30
Our study has several limitations. It is possible that the exclusion from analysis of those African American, Latino, and non-Hispanic white subjects who did not endorse at least a screening item (depressed mood, anhedonia, insomnia, or low energy) may have led to reduced variance in the response to the PHQ-9 overall. This reduced variance may account for the lack of difference we saw in the function and dimensionality of the PHQ-9 between groups. Finally, while the construct validity of the PHQ-9 has been examined in a separate analysis of these data, 39
convergent validity of the PHQ-9 in these different ethnic groups with an independent criterion standard such as the SCID would also be a valuable future study.
In light of the growing diversity of the U.S. population and the increasingly recognized importance of screening for depression in clinical care, the need for an efficient depression screening instrument that can be used in disparate groups is critical. Our study suggests that the PHQ-9 can be used without adjustment in different racial/ethnic groups and be a useful tool to help meet the mental health care needs of diverse populations.