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
Britt DM, Cohen LM, Collins FL, Cohen ML. Cigarette smoking and chewing gum: response to a laboratory-induced stressor. Health Psychol. 2001 Sep 1;20(5):361-8.