[1] NIEHS, Epidemiol Branch, Res Triangle Pk, NC 27709 USA
[2] NIEHS, Biostat Branch, Res Triangle Pk, NC 27709 USA
[3] CODA Res Inc, Res Triangle Pk, NC USA
[4] New England Med Ctr, Dept Neurol, Boston, MA 02111 USA
[5] SUNY Hlth Sci Ctr, Dept Neurol, Syracuse, NY 13210 USA