1. Department of Gerontology, Davis School of Gerontology, University of Southern California, 3715 McClintock Avenue, Los Angeles, CA 90089, 2Office of Population Research, Princeton University, Wallace Hall, Princeton, NJ 08544, 3Department of Electrical Engineering, University of Southern California, 3740 McClintock Avenue, and 4Department of Psychology, University of Southern California, 3620 McClintock Avenue, Los Angeles, CA 90089, USA