Pervious and impervious pavement reduce production and decrease lifespan of fine roots of mature Sweetgum trees

Root zones of mature Sweetgum paved with either pervious or impervious concrete after 15–18 years of tree growth exhibited much reduced standing fine root length compared to unpaved plots 3 years after pavement installation. The objective of this paper was to determine whether these observed reductions in standing root length were due to reduced root production rates or due to enhanced root mortality rates in response to the presence of either pavement. We measured both fine root production and root death over a 15-month period using biweekly nondestructive observations of the root zones at four depths. In addition, we used proportional hazards analysis to determine how the presence of pavement affected chances of root mortality. We found that new root production was more negatively affected by the presence of either pavement than root mortality while chances of root mortality were increased by the presence of pavement, leading to much reduced standing net root length in paved plots at any given time. Surprisingly, even though root production and mortality were strongly altered by pavement, there was no significant effect on tree diameter growth. These results suggest that while Sweetgum root dynamics are negatively affected by pavement, there is enough plasticity within this species to adapt to altered root zone dynamics without affecting aboveground growth.     

Exact Confidence Intervals for Proportions Estimated by Group Testing with Different Group Sizes

Group testing is the process of combining individual samples and testing them as a group for the presence of an attribute. The use of such testing to estimate proportions is an important statistical tool in many applications. When samples are collected and tested in groups of different size, complications arise in the construction of exact confidence intervals. In this case, the numbers of positive groups has a multivariate distribution, and the difficulty stems from a lack of a natural ordering of the sample points. Exact two‐sided intervals such as the equal‐tail method based on maximum likelihood estimation, and those based on joint probability or likelihood ratio statistics, have been previously considered. In this paper several new estimators are developed and assessed. We show that the combined tails (or Blaker) method based on a suitable ordering statistic, is the best choice in this setting. The methods are illustrated using a study involving the infection prevalence of Myxobolus cerebralis among free‐ranging fish.     

On the role of statistics in the palaeomagnetic proof of continental drift

Magnetized rocks provide a “tape recording” of the more recent history of the earth. It was this evidence that broke the opposition to continental drift. The nature of the data - samples of unit vectors in three dimensions - demanded new forms of statistical treatment. I hope that my personal account will enable the general statistician to see a rare example of statistics being developed to be a modest help in a major scientific revolution.     

Partially balanced incomplete block designs with two associate classes

We provide constructions of cyclic 2-class PBIBD's using cyclotomy in finite fields. Our results give theoretical explanations of the two sporadic examples given by Agrawal (1987).     

Is automatic enrollment consistent with a life cycle model?

We examine retirement saving for young adults in a life cycle model. We find that optimal retirement saving is zero for liquidity-constrained young adults who anticipate significant earnings growth. With a plausible age-earnings profile for college-educated workers, retirement saving does not begin until the late 30s or early 40s. Workers facing a flat earnings profile begin saving much sooner. Participating may be optimal for younger workers facing steep earnings profiles if they anticipate switching jobs and cashing out after 1–2 years. Our results suggest that automatically enrolling workers, regardless of age, is not consistent with a life cycle model.     

A Theory of Disagreement in Repeated Games With Bargaining

This paper proposes a new approach to equilibrium selection in repeated games with transfers, supposing that in each period the players bargain over how to play. Although the bargaining phase is cheap talk (following a generalized alternating‐offer protocol), sharp predictions arise from three axioms. Two axioms allow the players to meaningfully discuss whether to deviate from their plan; the third embodies a “theory of disagreement”—that play under disagreement should not vary with the manner in which bargaining broke down. Equilibria that satisfy these axioms exist for all discount factors and are simple to construct; all equilibria generate the same welfare. Optimal play under agreement generally requires suboptimal play under disagreement. Whether patient players attain efficiency depends on both the stage game and the bargaining protocol. The theory extends naturally to games with imperfect public monitoring and heterogeneous discount factors, and yields new insights into classic relational contracting questions.     

Housing policy and population problems in France

In this paper, the author describes the housing position in France to-day, and traces the reasons for the present housing shortage, which shows itself in the large number of old houses and the comparatively low level of building activity. This is traced to the history of rent restriction which has led to an increasing divergence between the restricted and the economic rent. The history of rent-restriction legislation is traced, and post-liberation measures of housing policy—both in the field of new house building and in the grant of housing allowances—are discussed.     

Dating for Older Women: Experiences and Meanings of Dating in Later Life

Research over the last 20 years has provided an increased understanding of intimate relationships in later life; however, dating in later life remains largely unexplored. The purpose of this study was to examine the meanings of dating for women in later life. In this study, dating was examined through semistructured, in-depth interviews with 14 women ages 64 to 77 who had all dated in later life. Themes that emerged from an interpretative phenomenological analysis included multiple meanings of dating in later life, how dating in later life compared to earlier points in life, and dating in the future.     

INDEX TO VOLUME 8 (1 990)

This article provides a simple shrinkage representation that describes the operational characteristics of various forecasting methods designed for a large number of orthogonal predictors (such as principal components). These methods include pretest methods, Bayesian model averaging, empirical Bayes, and bagging. We compare empirically forecasts from these methods with dynamic factor model (DFM) forecasts using a U.S. macroeconomic dataset with 143 quarterly variables spanning 1960–2008. For most series, including measures of real economic activity, the shrinkage forecasts are inferior to the DFM forecasts. This article has online supplementary material.     

Simultaneous Confidence Bands for Linear Regression with Covariates Constrained in Intervals

Abstract. The focus of this article is on simultaneous confidence bands over a rectangular covariate region for a linear regression model with k>1 covariates, for which only conservative or approximate confidence bands are available in the statistical literature stretching back to Working & Hotelling (J. Amer. Statist. Assoc. 24 , 1929; 73–85). Formulas of simultaneous confidence levels of the hyperbolic and constant width bands are provided. These involve only a k‐dimensional integral; it is unlikely that the simultaneous confidence levels can be expressed as an integral of less than k‐dimension. These formulas allow the construction for the first time of exact hyperbolic and constant width confidence bands for at least a small k(>1) by using numerical quadrature. Comparison between the hyperbolic and constant width bands is then addressed under both the average width and minimum volume confidence set criteria. It is observed that the constant width band can be drastically less efficient than the hyperbolic band when k>1. Finally it is pointed out how the methods given in this article can be applied to more general regression models such as fixed‐effect or random‐effect generalized linear regression models.