Subpopulation triage: How to allocate conservation effort among populations

Threatened species often exist in a small number of isolated subpopulations. Given limitations on conservation spending, managers must choose from strategies that range from managing just one subpopulation and risking all other subpopulations to managing all subpopulations equally and poorly, thereby risking the loss of all subpopulations. We took an economic approach to this problem in an effort to discover a simple rule of thumb for optimally allocating conservation effort among subpopulations. This rule was derived by maximizing the expected number of extant subpopulations remaining given n subpopulations are actually managed. We also derived a spatiotemporally optimized strategy through stochastic dynamic programming. The rule of thumb suggested that more subpopulations should be managed if the budget increases or if the cost of reducing local extinction probabilities decreases. The rule performed well against the exact optimal strategy that was the result of the stochastic dynamic program and much better than other simple strategies (e.g., always manage one extant subpopulation or half of the remaining subpopulation). We applied our approach to the allocation of funds in 2 contrasting case studies: reduction of poaching of Sumatran tigers (Panthera tigris sumatrae) and habitat acquisition for San Joaquin kit foxes (Vulpes macrotis mutica). For our estimated annual budget for Sumatran tiger management, the mean time to extinction was about 32 years. For our estimated annual management budget for kit foxes in the San Joaquin Valley, the mean time to extinction was approximately 24 years. Our framework allows managers to deal with the important question of how to allocate scarce conservation resources among subpopulations of any threatened species

Analysis of a longitudinal ordinal response clinical trial using dynamic models

In many areas of pharmaceutical research, there has been increasing use of categorical data and more specifically ordinal responses. In many cases, complex models are required to account for different types of dependences among the responses. The clinical trial that is considered here involved patients who were required to remain in a particular state to enable the doctors to examine their heart. The aim of this trial was to study the relationship between the dose of the drug administered and the time that was spent by the patient in the state permitting examination. The patient's state was measured every second by a continuous Doppler signal which was categorized by the doctors into one of four ordered categories. Hence, the response consisted of repeated ordinal series. These series were of different lengths because the drug effect wore off faster (or slower) on certain patients depending on the drug dose administered and the infusion rate, and therefore the length of drug administration. A general method for generating new ordinal distributions is presented which is sufficiently flexible to handle unbalanced ordinal repeated measurements. It consists of obtaining a cumulative mixture distribution from a Laplace transform and introducing into it the integrated intensity of a binary logistic, continuation ratio or proportional odds model. Then, a multivariate distribution is constructed by a procedure that is similar to the updating process of the Kalman filter. Several types of history dependences are proposed. Copyright 2004 Royal Statistical Society.

Investigating design for survival models

Accelerated life tests, Compound criteria, Compromise design, D-optimality, Frailty models, P-optimality,

Impact of hormone replacement therapy use on mammographic screening outcomes

PURPOSE: This study aims to measure the impact of HRT use at the time of screening on rates of screen-detected invasive breast cancer (IBC) and ductal carcinoma in situ(DCIS), interval cancers and investigative procedures, within a well-established population-based mammography screening program. METHODS: Using South Australian BreastScreen data from 1998 to 2009 pertaining to 819,722 screening episodes, Poisson regression models were undertaken to estimate the incidence risk ratios (IRR) for various screening outcomes at both the first and subsequent screening rounds, among women who had been using HRT in the 6 months prior to screening compared with those who had not. RESULTS: Current HRT use was associated with increased risk of recall for assessment, biopsy procedures, and breast cancer diagnosis among BreastScreen participants. Risk of screen-detected breast cancer was increased at subsequent screening rounds (IRR = 1.30, 95 % confidence interval 1.18–1.34), but not at women’s first screening round (1.05, 0.88–1.25). This increased risk applied to IBC (1.35, 1.27–1.45), but not to DCIS (1.04, 0.89–1.23). Interval cancer risk was elevated among HRT users following both the first screen (1.77, 1.33–2.37) and subsequent screening episodes (1.92, 1.72–2.15). CONCLUSIONS: Increased risks of recall, biopsy rates, screen detected, and interval cancers among HRT users have important implications for population-based breast cancer screening programs. Our findings support the concept that HRT use may increase the growth of preexisting cancers. Lack of effect on DCIS could imply different etiology or time frames forDCIS and IBC development or increased transition from preinvasive to invasive disease due to HRT use.Kerri R. Beckmann, Gelareh Farshid, David M. Roder, Janet E. Hiller and John W. Lync

Recording of hormone therapy and breast density in breast screening programs: summary and recommendations of the International Cancer Screening Network.

Item does not contain fulltextBreast density and the use of hormone therapy (HT) for menopausal symptoms alter the risk of breast cancer and both factors influence screening mammography performance. The International Cancer Screening Network (ICSN) surveyed its 29 member countries and found that few programs record breast density or the use of HT among screening participants. This may affect the ability of programs to assess their effectiveness in reducing breast cancer mortality. Seven countries recorded the use of HT at screening, and some were able to link screening records to individual prescribing records of HT. Eight countries reported recording breast density at screening mammography for some or all women screened. The recommendations of the ICSN for recording information about breast density and HT are presented.1 december 201