Results
There were 8,068 suicide deaths among residents of NYC between 1990 and 2006. Rates of suicide per 100,000 residents in NYC between 1990 and 2006 are presented in Table 1. Overall rates of suicide declined linearly from 8.1 per 100,000 people in 1990 to 4.8 per 100,000 people in 1999 and then remained relatively stable from 1999 through 2006. Longitudinal trends stratified by sex, age, and race are shown in Figure 1.
The results from our final GAM showing the association between the ICEI and the monthly rate of suicides per 100,000 NYC residents with smoothing functions to account for time trends are shown in Figure 2. There was a negative association between rates of suicide and the ICEI at values greater than 105, indicating that rates of suicide in NYC were lowest when economic activity was greatest.
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Figure 2.
Generalized additive model showing the association between the Index of Coincident Economic Indicators and the predicted monthly rate of violent suicides per 100,000 New York City (NYC) residents after accounting for time trends, 1990–2006. The points indicate the actual monthly rates of suicide per 100,000 residents of New York City. The solid line represents predicted values, and dotted lines indicate 95% confidence intervals.
We assessed the strength of the association between the ICEI and suicide rate by comparing rates of suicide at different values of the ICEI. On the basis of the posterior distribution of the parameters in our model, the predicted monthly rates of suicide per 100,000 persons were 0.54 (standard deviation = 0.03), 0.50 (standard deviation = 0.01), and 0.42 (standard deviation = 0.02) when the ICEI was at its lowest value of 99.8, its median monthly value of 108.9, and its highest value of 115.5, respectively (Table 2). This translated to a mean difference of −0.12 per 100,000 persons when comparing the predicted rate of suicide in a month when the ICEI was at its peak with that when the ICEI was at its nadir.
Web Figures 2–4 show results from our final GAM stratified by race/ethnicity, sex, and age, respectively. There was evidence that the association between ICEI and suicide varied by race/ethnicity, sex, and age, although the P value for the chi-squared test assessing interaction was less than 0.05 for race/ethnicity and sex but not age. The rate of suicide declined monotonically among whites, men, and adults less than 45 years of age as the ICEI increased from its nadir of 99.8 to its peak of 115.5. In contrast, there was evidence of nonlinear associations between the ICEI and rates of suicide for nonwhites, women, and adults 45 years of age or older, for whom the greatest rates of suicide were observed when the ICEI approached values of 107, 105, and 104, respectively. Predicted monthly rates of suicide at the lowest, median, and peak values of the ICEI from GAMs that accounted for time trends are shown in Table 2 for whites, nonwhites, men, women, adults less than 45 years of age, and adults 45 years of age or older.