Random Forests: some methodological insights

This paper examines from an experimental perspective random forests, the increasingly used statistical method for classification and regression problems introduced by Leo Breiman in 2001. It first aims at confirming, known but sparse, advice for using random forests and at proposing some complementary remarks for both standard problems as well as high dimensional ones for which the number of variables hugely exceeds the sample size. But the main contribution of this paper is twofold: to provide some insights about the behavior of the variable importance index based on random forests and in addition, to propose to investigate two classical issues of variable selection. The first one is to find important variables for interpretation and the second one is more restrictive and try to design a good prediction model. The strategy involves a ranking of explanatory variables using the random forests score of importance and a stepwise ascending variable introduction strategy

Enrollment Management Strategies as a Result of COVID-19 at Rural Community Colleges

Higher education institutions world-wide were impacted by the unprecedented novel coronavirus (COVID-19) beginning in early 2020. COVID-19 caused a disruption in services to students and resulted in pivots of teaching, learning, and student support. Community colleges differ from four-year counterparts through varying student demographics, funding sources, mission and foci, and student intentions. Community college enrollment is affected by economic, employment, and social trends. Enrollment management practices changes as campus operations for student support changed to remote support. COVID-19 forced administrators at colleges to make quick decisions. This study examined the perceptions of academic administrators at rural community colleges regarding how COVID-19 impacted enrollment management practices. This study aimed to determine the perceptions of changes occurring to enrollment management practices and the subsequent financial challenges resulting from COVID-19 within rural Virginia community colleges. Each rural community college in Virginia is included within the Rural Virginia Horseshoe, totaling 14 colleges. This study was a sequential explanatory study that was conducted in two phases. Phase One was a quantitative inquiry using a nonexperimental survey to gather mid to senior-level administrators’ perceptions of how COVID-19 was impacting enrollment management practices at their college. A total of 45 respondents completed the survey. The distribution included 102 mid to senior-level administrators. For the qualitative inquiry, the multiple case study research tradition was utilized. A total of 10 interviews were conducted with mid to senior-level administrators. Five themes emerged from the findings: (a) COVID-19 led to crisis management and operations in phases, (b) managing student onboarding during COVID-19, (c) COVID-19 created unique challenges for community college students, (d) COVID-19 affected decision making procedures, and (e) COVID-19 resulted in work/life balance issues and COVID fatigue. Major implications in the current study suggest that colleges should be ready to pivot to remote instruction or back from it, review the onboarding processes and supports to ensure that they are adequately serving students, and advocate to reduce the digital divide

Random Forests for Big Data

Big Data is one of the major challenges of statistical science and has numerous consequences from algorithmic and theoretical viewpoints. Big Data always involve massive data but they also often include online data and data heterogeneity. Recently some statistical methods have been adapted to process Big Data, like linear regression models, clustering methods and bootstrapping schemes. Based on decision trees combined with aggregation and bootstrap ideas, random forests were introduced by Breiman in 2001. They are a powerful nonparametric statistical method allowing to consider in a single and versatile framework regression problems, as well as two-class and multi-class classification problems. Focusing on classification problems, this paper proposes a selective review of available proposals that deal with scaling random forests to Big Data problems. These proposals rely on parallel environments or on online adaptations of random forests. We also describe how related quantities -- such as out-of-bag error and variable importance -- are addressed in these methods. Then, we formulate various remarks for random forests in the Big Data context. Finally, we experiment five variants on two massive datasets (15 and 120 millions of observations), a simulated one as well as real world data. One variant relies on subsampling while three others are related to parallel implementations of random forests and involve either various adaptations of bootstrap to Big Data or to "divide-and-conquer" approaches. The fifth variant relates on online learning of random forests. These numerical experiments lead to highlight the relative performance of the different variants, as well as some of their limitations

The effects of predation risk on phenotypic and hatching time variation in fathead minnow (pimephales promelas) embryos

Predation has long been recognized as a strong selective force influencing the behaviour, morphology and life history traits of prey species. Some prey species have the ability to alter their phenotypes in response to predation threat, to decrease their chances of being detected, caught and/or consumed by predators. It has also been demonstrated that some species have control over the timing of transition between one specific life stage and the next. This ability gives the prey control over how much time it spends in a risky stage. A particularly vulnerable stage for many prey fishes is that of the embryo, as they are a major prey item for many invertebrate and vertebrate predators. As such, strong selection pressure should exist for the development of anti-predator defenses specific for this time period. In a series of four experiments I assessed the ability of fathead minnow embryos to alter their hatching time and/or phenotype in response to various predation threats. In the first three experiments injured embryo cue was used to simulate a predation threat, as it has been shown to represent a general predation risk for many aquatic animals. In the fourth experiment predator odour was used in conjunction with injured embryo cues. Results of a power analysis conducted on the first three experiments determined with 95% confidence that fathead minnow embryos do not alter their hatch time in response to injured embryo cues. However, the embryos in the predation treatment did hatch with an altered phenotype; fry were significantly smaller (total body length) when exposed to predation cues. In the fourth experiment the embryos hatched with the same altered morphology in response to injured embryo cues combined with predator cues. Moreover, in this experiment the embryos hatched faster in the predation treatment than the control treatment. This is the first empirical evidence that fish can alter their hatching time in response to predation

Colonized and Racist Indigenous Campus Tour: Research-in-Brief

This Research-in-Brief explores the macro-structural aspects of college campuses and environments to understand how higher education institutions have created, maintained, and justified hostile campus climates against Indigenous students. It uncovers the embedded racist and genocidal values that are often cherished through dominant campus tours. This includes addressing how an incomplete understanding of history leads to centering oppressive values that disenfranchise Indigenous students in higher education. Offered is an abbreviated interpretation of the concept of Power and Place (Deloria & Wildcat, 2001), centering critical Indigenous values in the assessment. The case study articulates the historical and contemporary aspects of space and place in higher education. The authors embark upon a virtual racist campus tour by rearticulating typical campus tour components: history, student life, academic life, and campus leadership through a critical Indigenous approach. Lastly, recommendations are offered who wish to engage in work that dismantles educational systemic racism

Colonized and Racist Indigenous Campus Tour

This article explores the macro-structural aspects of college campuses and environments to understand how higher education institutions have created, maintained, and justified hostile campus climates against Indigenous students. It uncovers the embedded racist and genocidal values that are often cherished through dominant campus tours. This includes addressing how an incomplete understanding of history leads to centering oppressive values that disenfranchise Indigenous students in higher education. Offered is an abbreviated interpretation of the concept of Power and Place (Deloria & Wildcat, 2001), centering critical Indigenous values in the assessment. The case study articulates the historical and contemporary aspects of space and place in higher education. The authors embark upon a virtual racist campus tour by rearticulating typical campus tour components: history, student life, academic life, and campus leadership through a critical Indigenous approach. Lastly, recommendations are offered who wish to engage in work that dismantles educational systemic racism

Giving in Illinois, 2015

Illinois is home to over 5,200 grantmaking foundations spanning all types—independent or family, corporate, community, and operating—sizes, and issue areas. The community includes many foundations that only give locally or within the state, as well as those that fund nationally and even internationally. The following analysis provides an overview of the scale and composition of the Illinois foundation community and an examination of how Illinois foundations have fared relative to U.S. foundations in general over the past decade