Shrinkage estimation and the use of additional information when calibrating in the presence of random effects.

Let x denote a precise measurement of a quantity and Y an inexact measurement, which is, however, less expensive or more easily obtained than x. We have available a calibration set comprising clustered sets of (x,Y) observations, obtained from different sampling units. At the prediction step, we will only observe Y for a new unit, and we wish to estimate the corresponding unknown x, which we denote by ξ. This problem has been treated under the assumption that x and Y are linearly related. Here, we expand on those results in three directions: First, we show that if we center ξ about a known value c, for example, the mean x-value of the calibration set, then the proposed estimator now shrinks to c. Second, we examine in detail the performance of the estimator, which was proposed when one or more (x,Y) observations can be obtained for the new subject. Third, we compare the Fieller-like confidence intervals, previously proposed, with t-like intervals based on asymptotic moments of the point estimate. We illustrate and evaluate our procedures in the context of a data set of true bladder-volumes (x) and ultrasound measurements (Y).

Analyzing spatially distributed binary data using independent-block estimating equations.

We estimate the relation between binary responses and corresponding covariate vectors, both observed over a large spatial lattice. We assume a hierarchical generalized linear model with probit link function, partition the lattice into blocks, and adopt the working assumption of independence between the blocks to obtain an easily solved estimating equation. Standard errors are obtained using the "sandwich" estimator together with window subsampling (Sherman, 1996, Journal of the Royal Statistical Society, Series B58, 509-523). We apply this to a large data set describing long-term vegetation growth, together with two other approximate-likelihood approaches: pairwise composite likelihood (CL) and estimation under a working assumption of independence. The independence and CL methods give similar point estimates and standard errors, while the independent-block approach gives considerably smaller standard errors, as well as more easily interpretable point estimates. We present numerical evidence suggesting this increased efficiency may hold more generally.

Effect of combined insecticide sprays and sanitation techniques on population dynamics of Ceratitis capitata (Diptera: Tephritidae) in the central mountains of Israel.

We conducted an environmental manipulation study over a 7-km2 area to examine the effect of different control levels on the population dynamics of Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) in the central mountains of Israel. Adult male monitoring was carried out from spring to fall during 1988-1991 and year-round from 1994 to 2001. From 1995 to 1997, we manipulated the study area, imposing different levels of control by using a combination of insecticide sprays, tree pruning and removal, and fruit stripping. In the years preceding the manipulation, population dynamics was characterized by a peak summer population size in June-July, followed by a population decrease in August, leading to an early fall peak in September-October. If flies overwinter locally, we expected the intensive control to decrease the early summer population after the control. If flies do not overwinter locally, the control and sanitation activities should not decrease the population level in the following summer. During the entire period discussed, no flies were captured between January and May. The first appearance was recorded in late May or early June, reaching a peak in July. Regardless of control level and extent, the early summer peak remained unchanged during the entire study period, whereas the later fall peak decreased as host density decreased. We suggest that the first peak is the result of a seasonal reinvading population, whereas the later peak is governed by host availability and multiplication of the invading flies. The meaning and possible practical implications of our findings are discussed.

Inability of Ceratitis capitata (Diptera: Tephritidae) to overwinter in the Judean hills.

The overwintering potential of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), in cold winter areas within its northern distribution is a key element in understanding its ecology. Recent studies have suggested that although originating in tropical Africa, the fly has become adapted to the cold weather that prevails within its northernmost areas of distribution. We address the question of whether the Mediterranean fruit fly has expanded its overwintering range to include the mountains of central Israel. Doing so would imply that the fly has developed either a behavioral or a physiological mechanism to cope with low temperature and/or damp conditions in combination with cold. We monitored adult populations year round, sampling fruit, calculating expected emergence days for overwintering flies, and studying adults captured within dense and sparse apple orchards. We also performed several manipulative experiments to study preimago ability to survive the winter under natural or seminatural conditions. The study was conducted in the central mountains of Israel at 700-m altitude from 1994 to 2003. Comparison experiments also were conducted at 400 m and at sea level. Our results show 1) no adults captured during the winter and spring, 2) an absence of new infestations during the winter and spring, and 3) inability of preimago stages to overwinter in the central mountains of Israel. Thus, we conclude that the fly does not overwinter in the central mountains of Israel. We discuss the ecological and applied significance of our findings.