5,862 research outputs found
Learning and Visceral Temptation in Dynamic Savings Experiments
In models of optimal savings with income uncertainty and habit formation, people
should save early to create a buffer stock, to cushion bad income draws and limit
the negative internality from habit formation. In experiments in this setting,
people save too little initially, but learn to save optimally within four repeated
lifecycles, or 1-2 lifecycles with âsocial learning.â Using beverage rewards (cola)
to create visceral temptation, thirsty subjects who consume immediately
overspend compared to subjects who only drink after time delay. The relative
overspending of immediate-consumption subjects is consistent with hyperbolic
discounting and dual-self models. Estimates of the present-bias choices are
ÎČ=0.6-0.7, which are consistent with other studies (albeit over different time
horizons)
Learning and Visceral Temptation in Dynamic Saving Experiments
This paper tests two explanations for apparent undersaving in life cycle models: bounded rationality and a preference for immediacy. Each was addressed in a separate experimental study. In the first study, subjects saved too little initiallyâproviding evidence for bounded rationalityâbut learned to save optimally within four repeated life cycles. In the second study, thirsty subjects who consume beverage sips immediately, rather than with a delay, show greater relative overspending, consistent with quasi-hyperbolic discounting models. The parameter estimates of overspending obtained from the second study, but not the first, are in range of several empirical studies of saving (with an estimated ÎČ = 0.6â0.7)
The Impact of After School Tutoring on Math Achievement: Perceptions of African American Males and Those Who Teach Them
Despite increases in overall academic achievement, African American males continue to struggle in the area of mathematics. Data from the National Assessment of Educational Progress (NAEP) indicates that eighth grade African American males had the lowest levels of mathematics success of all subgroups in 2013, with only 13% performing at or above the proficient performance level in math. An approach to increasing the academic achievement of African American males has been to provide extended learning time beyond the typical secondary education experience. After school programs are one such example. Many studies indicate that after school programs have had some positive effects on math achievement. However, missing from the literature are qualitative studies that examine the impact of after school programs specifically on math achievement for African American males from the perspectives of the students and teachers involved in the programs. This qualitative study explores the experiences and perceptions of five African American male middle school students and three math teachers who tutor in an after school program at one middle school in southern California. The purpose of the study was to understand, from their perspective, the factors that were internal and external to the after school program that supported or challenged math achievement. Document analysis, observations of studentsâ regular math class and after school class, and participant interviews revealed the influence that teachers, pedagogy, attendance, peers and educational structure had on student engagement and studentsâ intrinsic motivation to learn math. This study exposes the complexity of raising math achievement even when students are given a second chance. It has important implications for educators, school program directors and school administrators who are engaged in efforts to increase the math achievement of African American male students
Increased hazard of myocardial infarction with insulinâprovision therapy in actively smoking patients with diabetes mellitus and stable ischemic heart disease: The BARI 2D (Bypass Angioplasty Revascularization Investigation 2 Diabetes) trial
Background
In the BARI 2D (Bypass Angioplasty Revascularization Investigation 2 Diabetes) trial, randomization of diabetic patients with stable ischemic heart disease to insulin provision (
IP
) therapy, as opposed to insulin sensitization (
IS
) therapy, resulted in biochemical evidence of impaired fibrinolysis but no increase in adverse clinical outcomes. We hypothesized that the prothrombotic effect of
IP
therapy in combination with the hypercoagulable state induced by active smoking would result in an increased risk of myocardial infarction (
MI
).
Methods and Results
We analyzed
BARI
2D patients who were active smokers randomized to
IP
or
IS
therapy. The primary end point was fatal or nonfatal
MI
.
PAI
â1 (plasminogen activator inhibitor 1) activity was analyzed at 1, 3, and 5Â years. Of 295 active smokers,
MI
occurred in 15.4% randomized to
IP
and in 6.8% randomized to
IS
over the 5.3Â years (
P
=0.023).
IP
therapy was associated with a 3.2âfold increase in the hazard of
MI
compared with
IS
therapy (hazard ratio: 3.23; 95% confidence interval, 1.43â7.28;
P
=0.005). Baseline
PAI
â1 activity (19.0 versus 17.5Â Au/mL,
P
=0.70) was similar in actively smoking patients randomized to
IP
or
IS
therapy. However,
IP
therapy resulted in significantly increased
PAI
â1 activity at 1Â year (23.0 versus 16.0Â Au/mL,
P
=0.001), 3Â years (24.0 versus 18.0Â Au/mL,
P
=0.049), and 5Â years (29.0 versus 15.0Â Au/mL,
P
=0.004) compared with
IS
therapy.
Conclusions
Among diabetic patients with stable ischemic heart disease who were actively smoking,
IP
therapy was independently associated with a significantly increased hazard of
MI
. This finding may be explained by higher
PAI
â1 activity in active smokers treated with
IP
therapy.
Clinical Trial Registration
URL
:
http://www.clinicaltrials.gov
. Unique identifier:
NCT
00006305.
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Association of inferior vena cava filter placement for venous thromboembolic disease and a contraindication to anticoagulation with 30-day mortality
Importance: Despite the absence of data from randomized clinical trials, professional societies recommend inferior vena cava (IVC) filters for patients with venous thromboembolic disease (VTE) and a contraindication to anticoagulation therapy. Prior observational studies of IVC filters have suggested a mortality benefit associated with IVC filter insertion but have often failed to adjust for immortal time bias, which is the time before IVC filter insertion, during which death can only occur in the control group.
Objective: To determine the association of IVC filter placement with 30-day mortality after adjustment for immortal time bias.
Design, Setting, and Participants: This comparative effectiveness, retrospective cohort study used a population-based sample of hospitalized patients with VTE and a contraindication to anticoagulation using the State Inpatient Database and the State Emergency Department Database, part of the Healthcare Cost and Utilization Project of the Agency for Healthcare Research and Quality, from hospitals in California (January 1, 2005, to December 31, 2011), Florida (January 1, 2005, to December 31, 2013), and New York (January 1, 2005, to December 31, 2012). Data analysis was conducted from September 15, 2015, to March 14, 2018.
Exposure: Inferior vena cava filter placement.
Main Outcomes and Measures: Multivariable Cox proportional hazard models were constructed with IVC filters as a time-dependent variable that adjusts for immortal time bias. The Cox model was further adjusted using the propensity score as an adjustment variable.
Results: Of 126âŻ030 patients with VTE, 61âŻ281 (48.6%) were male and the mean (SD) age was 66.9 (16.6) years. In this cohort, 45âŻ771 (36.3%) were treated with an IVC filter, whereas 80âŻ259 (63.7%) did not receive a filter. In the Cox model with IVC filter status analyzed as a time-dependent variable to account for immortal time bias, IVC filter placement was associated with a significantly increased hazard ratio of 30-day mortality (1.18; 95% CI, 1.13-1.22; Pâ\u3câ.001). When the propensity score was included in the Cox model, IVC filter placement remained associated with an increased hazard ratio of 30-day mortality (1.18; 95% CI, 1.13-1.22; Pâ\u3câ.001).
Conclusions and Relevance: After adjustment for immortal time bias, IVC filter placement was associated with increased 30-day mortality in patients with VTE and a contraindication to anticoagulation. Randomized clinical trials are needed to determine the efficacy of IVC filter placement in patients with VTE and a contraindication to anticoagulation
original antigenic Sin: the Downside of Immunological Memory and Implications For Covid-19
The concept of original antigenic sin (OAS) was put forth many years ago to explain how humoral memory responses generated against one set of antigens can affect the nature of antibody responses elicited to challenge infections or vaccinations containing a similar but not identical array of antigens. Here, we highlight the link between OAS and the germinal center reaction (GCR), a process unique to activated B cells undergoing somatic hypermutation and class switch recombination. It is the powerful response of activated memory B cells and the accompanying GCR that establish the foundations of OAS. We apply these concepts to the current COVID-19 pandemic and put forth several possible scenarios whereby OAS may result in either beneficial or harmful outcomes depending, hypothetically, on prior exposure to antigens shared between SARS-CoV-2 and seasonal human coronaviruses (hCoVs) that include betacoronaviruses (e.g., HCoV-OC43 and HCoV-HKU1) and alphacoronaviruses (e.g., HCoV-NL63 and HCoV-HKU1) (E. M. Anderson, E. C. Goodwin, A. Verma, C. P. Arevalo, et al., medRxiv, 2020, https://doi.org/10.1101/2020.11.06.20227215; S. M. Kissler, C. Tedijanto, E. Goldstein, Y. H. Grad, and M. Lipsitch, Science 368:860-868, 2020, https://doi.org/10.1126/science.abb5793)
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