Origin
The Perceived Stress Scale was developed by Sheldon Cohen and colleagues to measure the degree to which individuals appraise situations in their lives as stressful — specifically, how unpredictable, uncontrollable, and overloaded respondents find their lives (Cohen, Kamarck & Mermelstein, 1983). The original instrument contained 14 items; Cohen and Williamson (1988) subsequently introduced shorter 10-item and 4-item forms.
The PSS-4 is the ultra-brief version, designed for telephone interviews and contexts where respondent burden must be minimised.
What it measures
Rather than counting specific stressful events, the PSS measures perceived stress — the subjective appraisal that is theoretically more closely tied to health outcomes than objective event counts (Lazarus & Folkman, 1984). The four items ask, over the past month, how often the respondent felt unable to control important things, confident about handling personal problems (reverse-scored), that things were going their way (reverse-scored), and that difficulties were piling up beyond their ability to cope.
Psychometric standing
As a 4-item measure, the PSS-4 trades internal-consistency reliability for brevity; the authors and subsequent reviewers note it is best suited to large-sample or screening contexts rather than individual diagnosis (Cohen & Williamson, 1988; Warttig et al , 2013).
It correlates with the longer forms and with health and affective outcomes, supporting its use as a quick global index of perceived stress.