Warttig SL, Forshaw MJ, South J, White AK. New, normative, English-sample data for the Short Form Perceived Stress Scale (PSS-4). J Health Psychol. 2013 Dec;18(12):1617-28. doi: 10.1177/1359105313508346
Nguyen USDT, Rothman KJ, Demissie S, Jackson DJ, Lang JM, Ecker JL. Transfers among women intending a birth center delivery in the San Diego birth center study. J Midwifery Womens Health. 2009 Mar 1;54(2):104-10.