Why Model?

This address treats some enduring misconceptions about modeling. One of these is that the goal is always prediction. The lecture distinguishes between explanation and prediction as modeling goals, and offers sixteen reasons other than prediction to build a model. It also challenges the common assumption that scientific theories arise from and 'summarize' data, when often, theories precede and guide data collection; without theory, in other words, it is not clear what data to collect. Among other things, it also argues that the modeling enterprise enforces habits of mind essential to freedom. It is based on the author's 2008 Bastille Day keynote address to the Second World Congress on Social Simulation, George Mason University, and earlier addresses at the Institute of Medicine, the University of Michigan, and the Santa Fe Institute.[No keywords]

Social Conformity Despite Individual Preferences for Distinctiveness

We demonstrate that individual behaviors directed at the attainment of distinctiveness can in fact produce complete social conformity. We thus offer an unexpected generative mechanism for this central social phenomenon. Specifically, we establish that agents who have fixed needs to be distinct and adapt their positions to achieve distinctiveness goals, can nevertheless self-organize to a limiting state of absolute conformity. This seemingly paradoxical result is deduced formally from a small number of natural assumptions, and is then explored at length computationally. Interesting departures from this conformity equilibrium are also possible, including divergence in positions. The effect of extremist minorities on these dynamics is discussed. A simple extension is then introduced, which allows the model to generate and maintain social diversity, including multimodal distinctiveness distributions. The paper contributes formal definitions, analytical deductions, and counterintuitive findings to the literature on individual distinctiveness and social conformity.Comment: 11 pages, 6 figures, appendi

Upstream Geomorphic Response to Dam Removal: The Blackfoot River, Montana

As dam removal is increasingly used as a tool to restore rivers, developing a conceptual and field-based understanding of the upstream fluvial response is critical. Using empirical data and modeling, I investigated the spatial and temporal pattern of reservoir sediment erosion and upstream channel evolution of the Blackfoot River, MT, following the 8 m base level reduction caused by the removal of Milltown Dam. Field data collected include surveys of channel bed topography and water surface elevation profiles which were integrated into a flow modeling approach. Headward erosion extended 4.5 km upstream of the dam site during the first five months following the dam removal. In the lower 1.8 km of the reservoir, up to 3 m of highly mobile silt and sand was evacuated. Upstream, the river incised into a coarse deltaic sediment deposit (D50 70mm) in the upper reservoir. The analysis of erosion through the hydrograph shows that the channel incised up to 2 m in some locations and maximum volumetric erosion of 260,000 m3 was reached several days after the flood peak (286 m3/s, 3.5 year return interval). Net erosion following the dam removal, accounting for both scour and deposition, was 150,000 m3 across the 5 km study reach. The modeling-based water surface elevation analysis revealed the intra-hydrograph pattern of erosion that otherwise would have been missed by comparing pre- and post-removal cross section topography. The post-removal evolution of the lower Blackfoot was heavily influenced by confinement of the channel and the above average discharge. Widening was associated with areas of local aggradation, whereas narrowing was associated with degradation—a finding similar to those from previous flume experiments

Social Mobilization and the Process of Leadersip

field study proposal on the importance of persuasive communication and symbolic processes in palauan attempts at indigenous modernization along with bibliograph

The inevitability of unconditionally deleterious substitutions during adaptation

Studies on the genetics of adaptation typically neglect the possibility that a deleterious mutation might fix. Nonetheless, here we show that, in many regimes, the first substitution is most often deleterious, even when fitness is expected to increase in the long term. In particular, we prove that this phenomenon occurs under weak mutation for any house-of-cards model with an equilibrium distribution. We find that the same qualitative results hold under Fisher's geometric model. We also provide a simple intuition for the surprising prevalence of unconditionally deleterious substitutions during early adaptation. Importantly, the phenomenon we describe occurs on fitness landscapes without any local maxima and is therefore distinct from "valley-crossing". Our results imply that the common practice of ignoring deleterious substitutions leads to qualitatively incorrect predictions in many regimes. Our results also have implications for the substitution process at equilibrium and for the response to a sudden decrease in population size.Comment: Corrected typos and minor errors in Supporting Informatio

Unmarked? Criminal Record Clearing and Employment Outcomes

An estimated one in three American adults has a criminal record. While some records are for serious offenses, most are for arrests or relatively lowlevel misdemeanors. In an era of heightened security concerns, easily available data, and increased criminal background checks, these records act as a substantial barrier to gainful employment and other opportunities. Harvard sociologist Devah Pager describes people with criminal records as “marked” with a negative job credential. In response to this problem, lawyers have launched unmarking programs to help people take advantage of legal record clearing remedies. We studied a random sample of participants in one such program to analyze the impact of the record clearing intervention on employment outcomes. Using methods to control for selection bias and the effects of changes in the economy in our data, we found evidence that: (1) the record clearing intervention boosted participants’ employment rates and average real earnings, and (2) people sought record clearing remedies after a period of suppressed earnings. More research needs to be done to understand the durability of the positive impact and its effects in different local settings and labor markets, but these findings suggest that the record clearing intervention makes a meaningful difference in employment outcomes for people with criminal records. The findings also suggest the importance of early intervention to increase employment opportunities for people with criminal records. Such interventions might include more legal services, but they might also include record clearing by operation of law or another mechanism that does not put the onus of unmarking on the person with a criminal record

Policy Response to Pandemic Influenza: The Value of Collective Action

This paper examines positive externalities and complementarities between countries in the use of antiviral pharmaceuticals to mitigate pandemic influenza. It demonstrates the presence of treatment externalities in simple SIR (susceptible-infectious-recovered) models and simulations of a Global Epidemiological Model. In these simulations, the pandemic spreads from city to city through the international airline network and from cities to rural areas through ground transport. While most treatment benefits are private, spillovers suggest that it is in the self-interest of high-income countries to pay for some antiviral treatment in low-income countries. The most cost-effective policy is to donate doses to the country where the outbreak originates; however, donating doses to low-income countries in proportion to their populations may also be cost-effective. These results depend on the transmissibility of the flu strain, its start date, the efficacy of antivirals in reducing transmissibility, and the proportion of infectious people who can be identified and treated.pandemic influenza, disease control externalities