Wednesday, this is what I found:
Depression and Socioeconomic Status
Despite inconsistencies in rates of depression found in epidemiological studies, and regardless of how depression or its symptoms are measured, most research shows an inverse relationship between socioeconomic status (SES) and depression, especially among women (Kohn, Dohrenwend, and Mirotznik, 1998; Dohrenwend et al., 1992). While evidence linking social class to depression is not as clear-cut as that linking gender to depression, mixed findings may be due to the variation in the criteria used to determine SES. It can be measured by years of education, income level, occupational prestige or a combination of these factors, such as the Nam criteria, which combines household income, education and occupation into a percentile score of social prestige (Nam and Power, 1965). In a review of the literature, Link, Lennon, and Dohrenwend (1993) found that rates of depression among members of low SES groups are approximately twice those of high SES groups.
http://www.researchforum.org/newsletter/Depression410.pdf
Are you suggesting to get a properly objective study, we would also have to know the socioeconomic ratios amongst the Witnesses, as compared to the general population? Has it been confirmed that they are statistically poorer than average?