Cyclic game dynamics driven by iterated reasoning

Recent theories from complexity science argue that complex dynamics are ubiquitous in social and economic systems. These claims emerge from the analysis of individually simple agents whose collective behavior is surprisingly complicated. However, economists have argued that iterated reasoning--what you think I think you think--will suppress complex dynamics by stabilizing or accelerating convergence to Nash equilibrium. We report stable and efficient periodic behavior in human groups playing the Mod Game, a multi-player game similar to Rock-Paper-Scissors. The game rewards subjects for thinking exactly one step ahead of others in their group. Groups that play this game exhibit cycles that are inconsistent with any fixed-point solution concept. These cycles are driven by a "hopping" behavior that is consistent with other accounts of iterated reasoning: agents are constrained to about two steps of iterated reasoning and learn an additional one-half step with each session. If higher-order reasoning can be complicit in complex emergent dynamics, then cyclic and chaotic patterns may be endogenous features of real-world social and economic systems.Comment: 8 pages, 4 figures, and supplementary informatio

Pooled analysis of WHO Surgical Safety Checklist use and mortality after emergency laparotomy

Background The World Health Organization (WHO) Surgical Safety Checklist has fostered safe practice for 10 years, yet its place in emergency surgery has not been assessed on a global scale. The aim of this study was to evaluate reported checklist use in emergency settings and examine the relationship with perioperative mortality in patients who had emergency laparotomy. Methods In two multinational cohort studies, adults undergoing emergency laparotomy were compared with those having elective gastrointestinal surgery. Relationships between reported checklist use and mortality were determined using multivariable logistic regression and bootstrapped simulation. Results Of 12 296 patients included from 76 countries, 4843 underwent emergency laparotomy. After adjusting for patient and disease factors, checklist use before emergency laparotomy was more common in countries with a high Human Development Index (HDI) (2455 of 2741, 89.6 per cent) compared with that in countries with a middle (753 of 1242, 60.6 per cent; odds ratio (OR) 0.17, 95 per cent c.i. 0.14 to 0.21, P <0001) or low (363 of 860, 422 per cent; OR 008, 007 to 010, P <0.001) HDI. Checklist use was less common in elective surgery than for emergency laparotomy in high-HDI countries (risk difference -94 (95 per cent c.i. -11.9 to -6.9) per cent; P <0001), but the relationship was reversed in low-HDI countries (+121 (+7.0 to +173) per cent; P <0001). In multivariable models, checklist use was associated with a lower 30-day perioperative mortality (OR 0.60, 0.50 to 073; P <0.001). The greatest absolute benefit was seen for emergency surgery in low- and middle-HDI countries. Conclusion Checklist use in emergency laparotomy was associated with a significantly lower perioperative mortality rate. Checklist use in low-HDI countries was half that in high-HDI countries.Peer reviewe

Global variation in anastomosis and end colostomy formation following left-sided colorectal resection

Background End colostomy rates following colorectal resection vary across institutions in high-income settings, being influenced by patient, disease, surgeon and system factors. This study aimed to assess global variation in end colostomy rates after left-sided colorectal resection. Methods This study comprised an analysis of GlobalSurg-1 and -2 international, prospective, observational cohort studies (2014, 2016), including consecutive adult patients undergoing elective or emergency left-sided colorectal resection within discrete 2-week windows. Countries were grouped into high-, middle- and low-income tertiles according to the United Nations Human Development Index (HDI). Factors associated with colostomy formation versus primary anastomosis were explored using a multilevel, multivariable logistic regression model. Results In total, 1635 patients from 242 hospitals in 57 countries undergoing left-sided colorectal resection were included: 113 (6·9 per cent) from low-HDI, 254 (15·5 per cent) from middle-HDI and 1268 (77·6 per cent) from high-HDI countries. There was a higher proportion of patients with perforated disease (57·5, 40·9 and 35·4 per cent; P < 0·001) and subsequent use of end colostomy (52·2, 24·8 and 18·9 per cent; P < 0·001) in low- compared with middle- and high-HDI settings. The association with colostomy use in low-HDI settings persisted (odds ratio (OR) 3·20, 95 per cent c.i. 1·35 to 7·57; P = 0·008) after risk adjustment for malignant disease (OR 2·34, 1·65 to 3·32; P < 0·001), emergency surgery (OR 4·08, 2·73 to 6·10; P < 0·001), time to operation at least 48 h (OR 1·99, 1·28 to 3·09; P = 0·002) and disease perforation (OR 4·00, 2·81 to 5·69; P < 0·001). Conclusion Global differences existed in the proportion of patients receiving end stomas after left-sided colorectal resection based on income, which went beyond case mix alone

Mastectomy Flap Thickness and Complications in Nipple-Sparing Mastectomy: Objective Evaluation using Magnetic Resonance Imaging

Background:. Ischemic complications after nipple-sparing mastectomy (NSM) have been associated with numerous variables. However, the impact of NSM flap thickness has been incompletely evaluated. Methods:. NSM flap thickness was determined for all NSMs from 2006 to 2016 with available pre- or postoperative breast magnetic resonance imaging (MRIs). Demographics and outcomes were stratified by those with and without ischemic complications. Results:. Of 1,037 NSM reconstructions, 420 NSMs had MRI data available, which included 379 preoperative MRIs and 60 postoperative MRIs. Average total preoperative skin/subcutaneous tissue NSM flap thickness was 11.4 mm. Average total postoperative NSM flap thickness was 8.7 mm. NSMs with ischemic complications were found to have significantly thinner overall postoperative NSM flap thickness compared with those without ischemic complications (P = 0.0280). Average overall postoperative NSM flap thickness less than 8.0 mm was found to be an independent predictor of ischemic complications (odds ratio, 6.5263; P = 0.026). In NSMs with both pre- and postoperative MRIs, the overall average postoperative NSM flap thickness was 68.2% of preoperative measurements. Average overall postoperative NSM flap thickness was significantly less than average overall preoperative NSM flap thickness (P < 0.0001). NSMs with ischemic complications were found to have a significantly lower ratio of overall postoperative to preoperative flap thickness (52.0% versus 74.0%; P < 0.0001). Conclusions:. Ischemic complications after NSM are significantly associated with thinner postoperative NSM flap thickness. Particularly, NSM flap thickness less than 8.0 mm is a positive independent predictor of ischemic complications. The ratio of postoperative to preoperative NSM flap thickness was significantly lower in reconstructions with ischemic complications

Optimizing Outcomes in Nipple-sparing Mastectomy: Mastectomy Flap Thickness Is Not One Size Fits All

Summary:. Nipple-sparing mastectomy (NSM) places greater stress on the breast-skin envelope compared with traditional mastectomy techniques. Precise mastectomy flap dissection is critical to optimize breast skin flap thickness and minimize complication risk. This study evaluated patient-specific factors associated with mastectomy flap quality to improve technical success in NSM. Ideal NSM flap thickness was determined for all NSMs from 2006 to 2016 with available preoperative breast magnetic resonance imaging (MRIs). Demographic, operative variables, and flap thickness were compared for NSMs as stratified by body mass index (BMI) and mastectomy weight. Of the 1,037 NSMs, 420 cases (40.5%; 243 patients) had MRI data available, which included 379 (36.5%) preoperative breast MRIs. Average BMI was 24.08 kg/m2, whereas average mastectomy weight was 442.28 g. NSMs were classified according to BMI 30 kg/m2. Average ideal overall NSM flap thicknesses in these groups were 10.43, 12.54, and 14.91 mm, respectively. Each incremental increase in average overall NSM flap thickness per BMI category was statistically significant (P < 0.0001; P < 0.0001; P = 0.0002). NSMs were also classified into mastectomy weight categories: <400 g, 400–799 g, and ≥800 g. Average overall NSM flap thicknesses in these groups were 9.97, 12.21, and 14.50 mm, respectively. Each incremental increase in average overall NSM flap thickness per mastectomy weight category was similarly statistically significant (P < 0.0001; P < 0.0001; P < 0.0001). NSM flap thickness and quality is related to BMI and breast size. Characterizing these anatomic variations preoperatively will help surgeons optimize mastectomy flap dissections and minimize ischemic complications in breast reconstruction after NSM

Examining Length of Hospital Stay after Microsurgical Breast Reconstruction: Evaluation in a Case-Control Study

Background:. While possessing numerous benefits, microsurgical breast reconstruction is associated with longer operative times and post-operative hospital length of stay compared to implant-based reconstruction. We therefore evaluate factors associated with increased length of stay (LOS) after microsurgical breast reconstruction with a case-control study design. Methods:. All patients undergoing immediate or delayed abdominally-based microsurgical breast reconstruction over a two-year time period were identified. Risk factors associated with LOS greater than or equal to 5 days were identified. Results:. A total of 116 patients undergoing immediate or delayed abdominally-based microsurgical breast reconstruction were identified. Of these, 86 (74.1%) had a LOS of 4 days or less (mean: 3.70 days) while 30 (25.9%) had a LOS of 5 days or greater (mean: 5.50 days). With regards to patient demographics and intra-operative factors, patients with a LOS of 5 days or greater were significantly more likely to have diabetes mellitus (p < 0.0001), undergo bilateral reconstruction (p = 0.0003) and total mastectomy (p < 0.0001), and have a longer operative time (p < 0.0001) while significantly less likely to undergo post-operative radiation (p = 0.0421). Notably, there was no significant difference between the groups in terms of follow-up time, or time since breast reconstruction (p = 0.0600). With regards to reconstructive complications, patients with LOS of 5 days of greater were significantly more likely to experience abdominal donor site abscess (p < 0.0001), breast hematoma (p = 0.0186), and return to the operating room for flap compromise (p < 0.0001). Conclusions:. Multiple patient-specific, intra-operative, and post-operative outcomes factors are associated with increased length of stay with immediate and delayed microsurgical breast reconstruction