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Working with data about homicide victims and perpetrators from 50 of America's largest cities, we investigate the explanatory power of some familiar explanations for why murder in those cities rose sharply in 2020. The analysis reveals that the distribution of risk by race was essentially the same in 2020 as in 2019. That empirical finding challenges some theories of how racial tensions after the death of George Floyd may have driven homicide increases. Similarly, homicide growth was not concentrated in those cities with the greatest availability in 2020 of new and older guns, or among the cities that suffered the most from the COVID-19 pandemic. At a minimum, the cross-city outcomes should reduce confidence that some combination of "race, guns, and COVID-19" explains all of the most important aspects of what happened in 2020., (© 2024 Society for Risk Analysis.)

We apply standard demographic principles of inflows and outflows to estimate the number of undocumented immigrants in the United States, using the best available data, including some that have only recently become available. Our analysis covers the years 1990 to 2016. We develop an estimate of the number of undocumented immigrants based on parameter values that tend to underestimate undocumented immigrant inflows and overstate outflows; we also show the probability distribution for the number of undocumented immigrants based on simulating our model over parameter value ranges. Our conservative estimate is 16.7 million for 2016, nearly fifty percent higher than the most prominent current estimate of 11.3 million, which is based on survey data and thus different sources and methods. The mean estimate based on our simulation analysis is 22.1 million, essentially double the current widely accepted estimate. Our model predicts a similar trajectory of growth in the number of undocumented immigrants over the years of our analysis, but at a higher level. While our analysis delivers different results, we note that it is based on many assumptions. The most critical of these concern border apprehension rates and voluntary emigration rates of undocumented immigrants in the U.S. These rates are uncertain, especially in the 1990's and early 2000's, which is when-both based on our modeling and the very different survey data approach-the number of undocumented immigrants increases most significantly. Our results, while based on a number of assumptions and uncertainties, could help frame debates about policies whose consequences depend on the number of undocumented immigrants in the United States., Competing Interests: The authors have declared that no competing interests exist.