Analysis of stress measures revealed a significant statistical interaction between group and phase. Further analysis indicated that this arose from the fact that on Day 6 the Guards were significantly more stressed than the Prisoners, and significantly more stressed than they had been on Day 2.
Analysis of the cortisol in participants’ saliva revealed a statistically significant effect for phase. Cortisol levels were higher on Day 6 than on Day 2. There was also a marginally significant interaction between group and phase, suggesting that this increase was more marked for the Guards than for the Prisoners.
- Source: Haslam, S. A. & Reicher, S. D. (2006). Stressing the group: Social identity and the unfolding dynamics of stress. Journal of Applied Psychology, 91, 1037–1052.