Ergodicity-breaking reveals time optimal decision making in humans

Ergodicity describes an equivalence between the expectation value and the time average of observables. Applied to human behaviour, ergodic theories of decision-making reveal how individuals should tolerate risk in different environments. To optimise wealth over time, agents should adapt their utility function according to the dynamical setting they face. Linear utility is optimal for additive dynamics, whereas logarithmic utility is optimal for multiplicative dynamics. Whether humans approximate time optimal behavior across different dynamics is unknown. Here we compare the effects of additive versus multiplicative gamble dynamics on risky choice. We show that utility functions are modulated by gamble dynamics in ways not explained by prevailing decision theories. Instead, as predicted by time optimality, risk aversion increases under multiplicative dynamics, distributing close to the values that maximise the time average growth of in-game wealth. We suggest that our findings motivate a need for explicitly grounding theories of decision-making on ergodic considerations

Colectomy in patients with acute colitis: a systematic review.

Contains fulltext : 81081.pdf (publisher's version ) (Closed access)BACKGROUND: For patients with acute colitis, the decision when and how to operate is difficult in most cases. It was the aim of this systematic review to analyze early mortality and morbidity of colectomy for severe acute colitis in order to identify opportunities to improve perioperative treatment and outcome. METHODS: A systematic review of the available literature in the Medline and PubMed databases from 1975 to 2007 was performed. All articles were assessed methodologically; the articles of poor methodological quality were excluded. Articles on laparoscopic colectomy for acute colitis were analyzed separately. RESULTS: In total, 29 studies met the criteria for the systematic review, describing a total of 2,714 patients, 1,257 of whom were operated on in an acute setting, i.e., urgent or emergency colectomy. Reported in-hospital mortality was 8.0%; the 30-day mortality was 5.2%. Morbidity was 50.8%. The majority of complications were of infectious and thromboembolic nature. Over the last three decades, there was a shift in indications from toxic megacolon, from 71.1% in 1975-1984 to 21.6% in 1995-2005, to severe acute colitis not responding to conservative treatment, from 16.5% in 1975-1984 to 58.1% in 1995-2007. Mortality decreased from 10.0% to 1.8%. Morbidity remained high, exceeding 40% in the last decade. Mortality after laparoscopic surgery was 0.6%. Complication rate varies from 16-37%. CONCLUSION: Colectomy for acute colitis is complicated by considerable morbidity. The incidence of adverse outcome has substantially decreased over the last three decades, but further improvements are still required. The retrospective nature of the included studies allows for a considerable degree of selection bias that limits robust and clinically sound conclusions about both conventional and laparoscopic surgery