Using population-based surveys of NYC adults in 2002 and 2003, we found that NPD was elevated compared to national estimates (6.4 vs. 3.0% in 2002 and 5.1 vs. 3.1% in 2003)3
but declined between 2002 and 2003. There are several possible explanations why the prevalence of NPD documented in this study was higher than in the rest of the country. First, it is possible that some of the differences documented here may be due to differences in the prevalence of primary risk factors for NPD such as low income,17–20
and not being married.4,18–22
In NYC, 21% of the population lives below the poverty level,23
compared to 12% nationwide.24
In 2003, 15% of New York respondents reported fair or poor health, compared to 12% of NHIS respondents, and 52% of CHS respondents were neither married nor living with a partner compared to 37% of respondents nationally.25
Second, this survey was conducted in the aftermath of the September 11 terrorist attacks. Previous work has shown that there were substantial psychological sequelae of the attacks in the general population of NYC in 2002 and 200326,27
and that levels of posttraumatic stress disorder (PTSD) symptoms were higher in New York City than in the rest of the country.28
It is likely that some of these psychopathological consequences of the attacks contributed to the NPD documented here. The decline in NPD between 2002 and 2003 observed in NYC, but not seen nationally, would favor this explanation.3
Third, characteristics of the survey and its administration may explain some of the observed differences. The CHS was conducted over the telephone, in contrast to the face-to-face NHIS interviews that provide national prevalence estimates. Respondents may have been more likely to report negative emotional states over the telephone than in face-to-face interviews. Also, some portion of the disparity between NHIS and CHS findings could be attributed to the fact that 11% of CHS respondents were interviewed in a language other than English, compared to 6% of NHIS respondents. The age-adjusted prevalence of NPD was 12.0% (95% CI: 10.1–14.2) among CHS respondents interviewed in Spanish and 6.4% (95% CI 4.1–9.7) among those interviewed in other foreign languages. However, even among CHS respondents interviewed in English, the prevalence of NPD is about 60% higher than the overall 2003 NHIS estimate (4.9% (95% CI: 4.5–5.3) vs. 3.1 (95% CI: 2.9–3.4).
Factors associated with NPD in this study are, for the most part, consistent with correlates identified in the literature. Our data confirm the previously observed protective mental health effect of marriage4,18–22
and an inverse linear relationship between income and NPD.2,17,20
We also found NPD to occur more frequently among individuals between the ages of 25 and 64 than among older individuals and found no difference in NPD prevalence between the youngest and oldest adults. These findings are consistent with those of the NHIS29
and Australian National Mental Health Survey4
but contrary to other research that shows middle age as the period with the least distress.30
As was found by the NHIS,29
our age-adjusted estimates show higher NPD prevalence among Hispanics and no difference between blacks and whites. After controlling for income, health status and the other factors in the multivariable model, however, NPD in NYC was less likely to occur among blacks than whites, and the increased rate among Hispanics was attenuated.
Other correlates of NPD observed in this study that have been documented elsewhere include gender,3,19,22
fair or poor health,18,19
diabetes or asthma,4
health care access,19
We also found higher rates of NPD among individuals whose telephone service had been interrupted for more than 24 h in the past year. We hypothesize that this variable is a marker for financial or personal disorganization that is independent of income. Unlike other studies,2,4
we found no relationship, after controlling for other factors, between body mass index and NPD. Nor did we observe an association between NPD and alcohol consumption.
We created a marker for exposure to the September 11 attacks that was based on residential proximity to the World Trade Center site but found no association between this variable and SPD. Movement of the most affected residents out of the area shortly after the attacks and the fact that most New Yorkers affected by the September 11 attacks were exposed to the trauma at their place of work, not in their home, may explain this finding.
The findings in this study are subject to a number of limitations. First, the sample represents only non-institutionalized adults with land-based telephones, thus excluding individuals who are homeless, undergoing residential psychiatric treatment, living in other group settings, and those without any telephone service or with only mobile phone service. While this limits generalizability, homeless individuals and those living in group-settings are also not represented in studies providing comparable national estimates, such as the NHIS. Second, the cross-sectional nature of the study prevents us from fully understanding the observed associations between NPD and its correlates. Nor can we measure the extent to which the decline in NPD is attributable to either recovery from the psychological sequelae of the September 11, 2001, attacks, or to the City's improving economic climate.33
Third, until we conduct a validation study of the K6 in NYC, we cannot be certain that the 12/13 cut-point used to distinguish cases from non-cases is optimal for this population. Fourth, the K6 has not been validated in Spanish. Bias introduced by use of a Spanish version of the K6 may account for some of the higher prevalence we observed in the Spanish language interviews, although it would not account for the observed higher prevalence of NPD overall. Fifth, the data are self-reported and do not include diagnostic measures of specific mental disorders.
In summary, the prevalence of NPD in NYC is high and occurs disproportionately among New Yorkers who are poor, in poor health, chronically unemployed, uninsured and formerly married. The prevalence of NPD declined between 2002 and 2003 but declined least among the groups with the highest prevalence. The excess prevalence of NPD in New York City has very high social and economic costs. Poor mental health (including intentional injuries) accounts for the second highest percentage of disability-adjusted life years (DALY's) in developed countries, second only to cardiovascular disease.34
The economic burden of mental disorders is shouldered by the individual sufferers, family and friends, employers and society, and includes economic and intrapersonal costs associated with care, absenteeism and lost productivity, comorbid physical disease, treatment side effects, premature death, personal anguish, stigma and social isolation.35
These findings suggest that we need both research to understand the etiology of this higher-than-expected NPD prevalence and a multi-faceted approach to promote mental health in New York City. Community-based interventions to reduce poverty, social isolation, community violence and other community-level risk factors for NPD may be warranted36
together with individual-level interventions to expand access to mental health assessment and to evidence-based pharmacologic and non-pharmacologic treatment.