The Impact of Time of Night on Affect and Affective State Type: A Simulated Nightshift Study.

Nightshift workers experience circadian misalignment thus negatively impacting many physiological systems which can change subjective states such as affect. The current study examined change in affect and affective state across a simulated first nightshift. Ninety sleep-deprived college students (33% female) completed a series of surveys and tasks across four testing sessions during the night. The participants completed the Positive and Negative Affect Schedule at the beginning of each testing session. Using these affect scores, we derived four affective state types defined by high and low positive and negative affect (Self-actualizing-high positive affect with low negative affect, High affective-high positive affect with high negative affect, Self-destructive-low positive affect with high negative affect, Low affective-low positive affect with low negative affect). A 2 (positive affect/negative affect) x 4 (time) repeated measures ANOVA was used to examine change over time in the positive and negative affect scores. A Friedman test with a Wilcoxon Signed Ranks test was performed to determine if there was a significant change in affective state across the four testing sessions. The current results indicate that positive affect decreased across the night while negative affect remained low and stable. The four derived affective states changed across the night with decreases in the high positive affective states, and increases in low positive affective states. These results suggests that nightshift workers experience stress-inducing conditions that negatively impact positive affect and affective state. Workers and organisations should anticipate decreased positive affect and positive affective states during nightshifts and consider appropriate mitigation strategies.