1. Department of Biostatistics; University of Alabama at Birmingham; Birmingham AL 35294 U.S.A.
2. Department of Psychology; State University of New York at Binghamton; Binghamton NY 13902 U.S.A.
3. Department of Statistics; Harvard University; Cambridge MA 02138 U.S.A.
4. Psychology Research Laboratory; McLean Hospital; 115 Mill Street Belmont MA 02478 U.S.A.