Recent Historical Data Research Articles

Comparison of Past and Recent Historical Control Data in Relation to Spontaneous Tumors During Carcinogenicity Testing in Fischer 344 Rats

In the present survey, the historical data for spontaneous tumors observed in our laboratory was compared in relation to the time-related changes between recent (2000-2004) and past (1990-1999) samples from Fischer 344 rats used in carcinogenicity studies. In the recent samples, there were statistically increased incidences of islet cell adenomas in males and uterine adenocarcinomas in females. On the other hand, there were decreased incidences of pheochromocytomas, prostatic adenomas, pituitary anterior adenomas, large granular lymphocytic (LGL) leukemias and Leydig cell tumors in males and pituitary anterior adenomas in females. Furthermore, there were decreases in the body weights of both sexes at 58 weeks of age in the recent samples, and this may have been related to the decreases in the incidences of pheochromocytomas, Leydig cell tumors, prostatic adenomas and LGL leukemias. Moreover, the decreased incidence of pheochromocytoma in males revealed a positive correlation with a decreased percentage of severe chronic progressive nephropathy (CPN). On the other hand, there were no distinct factors responsible for increased incidences of tumors observed in the recent samples, suggesting a possible genetic drift. In conclusion, the incidences of spontaneous tumors obtained in our laboratory have been changed with time. Smaller body weights in both sexes and reduction in the number of male cases with severe CPN might be related to the reduced incidence of certain types of tumors in recent animals.

Temperature difference across the Lomonosov Ridge: Implications for the Atlantic Water circulation in the Arctic Ocean

Drifting buoy observations in the Arctic Ocean indicate that, unlike climatological conditions, the temperature of the upper Atlantic water was higher in the Makarov Basin side of the Lomonosov Ridge than in the Amundsen Basin side in 2004. Hydrographic data from 1991 to 2004 has been compared with climatology to examine the relative phase of Atlantic water temperature change in these regions. On the Amundsen Basin side of the Lomonosov Ridge, a positive temperature anomaly in the Atlantic water began in the early 1990s, continued from the mid‐1990s to the early 2000s and started decreasing in 2004. In contrast, positive temperature anomalies were first apparent on the Makarov Basin side of the Lomonosov Ridge in 2000, and continue in 2004. Recent historical data indicates that the arrival of temperature anomalies on the Makarov Basin side of the Lomonosov Ridge is delayed about 7 years after arrival on the Amundsen Basin side. Our results support the idea that Atlantic Water circulates cyclonically around the periphery of the Makarov basin at a propagation speed of 1–2 cm s−1.

Are introduced and re‐introduced species comparable? A case study of birds

AbstractKnowledge of the causes of success or failure in introductions may provide information to help improve the chances that re‐introductions succeed. However, the utility of this information will be influenced by the comparability of sets of introduced and re‐introduced species. Here, we assess the extent of this similarity using recent historical data on introduced and re‐introduced birds. Introductions are less often threatened than expected and have larger ranges and earlier ages at maturity than re‐introductions. Introductions also generally have ‘weedy’ life‐history characteristics relative to family‐typical values, whereas those of re‐introductions more closely conform to these typical values. However, introductions and re‐introductions do not differ in migratory behaviour, mating system or dichromatism, nor do they show statistically consistent differences in body mass, incubation time or annual fecundity. The taxonomic composition of the lists of introductions and re‐introductions is similar, with more species than expected on both lists. Overall, these results suggest that the characteristics of introductions and re‐introductions are sufficiently similar that conclusions from studies of the former may reasonably be used to inform studies of the latter.

Impacts of land use and climate change on regional net primary productivity

Combined with recent historical climate data and two periods of land use data sets from remote sensing data, we test the net primary productivity (NPP) data sets in North China modelled by the satellite data-driven Global Production Efficiency Model (GLO-PEM) for detecting the widespread spatial and temporal characteristics of the impacts of climate and land use change on the regional NPP. Our results show that over the past 20 years, the mean annual temperature in the study region has remarkably increased by more than 0.064 °C, but over the same period, there has been a 1.49 mm decrease in annual precipitation and decrease in NPP by an annual rate of 6.9 TgC. The NPP changes in the study region were greatly affected by the average temperature and precipitation by ten-day periods as well as the seasonal temperature and precipitation in the study region. The correlation between seasonal NPP and seasonal precipitation and temperature is highly consistent with land cover spatially, and the correlation coefficient changes with the changes of vegetation types. The analysis reveals that the related areas in land use change only take up 5.45% of the whole studied region, so the climate changes dominate the impacts on the NPP in the whole study region (90% of the total). However, land use plays an absolute dominative role in areas with land cover changes, accounting for 97% of the total. From 1981 to 2000, the NPP in the whole study region remarkably reduced due to obvious precipitation decrease and temperature rise. Between two periods of land use (about 10 years), the changes in climate are predicted to promote a decrease in NPP by 78 (±0.6) TgC, and integrated impacts of climate changes and land use to promote a decrease in NPP by 87(±0.8) TgC.

Pro-Cyclicality, Empirical Credit Cycles, and Capital Buffer Formation

We model 1927-1997 U.S. business failure rates using a time series approach based on unobserved components. Clear evidence is found of cyclical behaviour in default rates. The cycle has a period of around 10 years. We also detect longer term movements in default rates and default correlations. In a credit risk experiment we show that accommodation of these default rate dynamics has important consequences for capitalisation requirements for credit risk. First, the static variants of credit risk portfolio models that are typically used by financial institutions and their regulators may significantly underestimate capital requirements for credit risk. Second, models that account for the observed dynamic behaviour of default rates do anticipate on required increases in capital, in contrast to models that only use recent historical default rate data. Hence, dynamic credit risk models may help to alleviate the problems of pro-cyclicality in capital requirements. Besides, we show that the size of the net margin is an important determinant of the level of capital needed. Ignoring the net margin in dynamic credit risk analyses may lead to overly conservative capital requirements.

Estimation Error in the Assessment of Financial Risk Exposure

Value at Risk and similar measures of financial risk exposure require predicting the of an asset returns distribution. Assuming a specific form, such as the normal, for the distribution, the standard deviation (and possibly other parameters) are estimated from recent historical data and the cutoff value is computed. But this standard procedure ignores estimation error, which we find to be substantial even under the best of conditions. In practice, a tail event may represent a truly rare occurrence, or it may simply be a not-so-rare occurrence at a time when the predicted volatility underestimates the true volatility, due to sampling error. This problem gets worse the further in the one is trying to predict. Using a simulation of 10,000 years of daily returns, we first examine estimation risk when volatility is an unknown constant parameter. We then consider the more realistic, but more problematical, case of volatility that drifts stochastically over time. This substantially increases estimation error, although strong mean reversion in the variance tends to dampen the effect. Non-normal fat-tailed return shocks makes overall risk assessment much worse, especially in the extreme tails, but estimation error per se does not add much beyond the effect of fatness. Using an exponentially weighted moving average to downweight older data hurts accuracy if volatility is constant or only slowly changing. But with more volatile variance, an optimal decay rate emerges, with better performance for the most extreme tails being achieved using a relatively greater rate of downweighting. We first simulate non-overlapping independent samples, but in practical risk management, risk exposure is estimated day by day on a rolling basis. This produces strong autocorrelation in the estimation errors, and bunching of apparently extreme events. We find that with stochastic volatility, estimation error can increase the probabilities of multi-day events, like three 1% events in a row, by several orders of magnitude. Finally, we report empirical results using 40 years of daily S&P 500 returns which confirm that the issues we have examined in simulations are also present in the real world.

Biosurveillance applying scan statistics with multiple, disparate data sources.

Researchers working on the Department of Defense Global Emerging Infections System (DoD-GEIS) pilot system, the Electronic Surveillance System for the Early Notification of Community-Based Epidemics (ESSENCE), have applied scan statistics for early outbreak detection using both traditional and nontraditional data sources. These sources include medical data indexed by International Classification of Disease, 9th Revision (ICD-9) diagnosis codes, as well as less-specific, but potentially timelier, indicators such as records of over-the-counter remedy sales and of school absenteeism. Early efforts employed the Kulldorff scan statistic as implemented in the SaTScan software of the National Cancer Institute. A key obstacle to this application is that the input data streams are typically based on time-varying factors, such as consumer behavior, rather than simply on the populations of the component subregions. We have used both modeling and recent historical data distributions to obtain background spatial distributions. Data analyses have provided guidance on how to condition and model input data to avoid excessive clustering. We have used this methodology in combining data sources for both retrospective studies of known outbreaks and surveillance of high-profile events of concern to local public health authorities. We have integrated the scan statistic capability into a Microsoft Access-based system in which we may include or exclude data sources, vary time windows separately for different data sources, censor data from subsets of individual providers or subregions, adjust the background computation method, and run retrospective or simulated studies.

Seasonal and inter-annual variations in the surface freshwater flux in the Mediterranean Sea from the ECMWF re-analysis project

Seasonal and inter-annual variations in surface freshwater fluxes in the Mediterranean Sea are examined. Evaporation and precipitation rates are estimated from ERA15, the re-analysis project carried out at the European Center for Medium-Range Weather Forecasts (ECMWF) for the period 1979–1993. A seasonal cycle of river runoff is computed from a recent historical data set. The climatological mean for precipitation (326 mm/yr) is comparable to previous estimates, whereas that for evaporation (920 mm/yr) is low compared to other independent estimates, but regions of high and low evaporation rates are correctly located. The budget reveals an annual mean freshwater deficit in the Mediterranean of 480 mm/yr, lower than previous estimates because of the lower evaporation rate estimated by ECMWF. Consequently, the flows through the straits of Gibraltar and Sicily, deduced from the freshwater budget, are found to be slightly low. Seasonal and inter-annual variabilities of ERA15 precipitation are consistent with those deduced from independent precipitation estimates obtained with SSM/I observations for the 1988–1993 period. ECMWF and satellite estimates both agree on the amplitude of the seasonal cycle. The seasonal cycle of the river runoff has a globally small contribution to the freshwater budget, but is significant in summer when the precipitation is nearly null. The variability of the freshwater flux for the Mediterranean as a whole shows a strong seasonal cycle (amplitude of 50 mm/month), which seems to be mainly controlled by evaporation. The inter-annual variability of the freshwater flux, however, appears to be governed mainly by precipitation. Its amplitude, which is of the order of 50 mm/yr on average but may reach nearly 150 mm/yr for a particular year, is considered to be large but nevertheless not sufficient to explain differences observed in the estimates of the climatological mean freshwater flux proposed by various authors. The freshwater deficit in the Mediterranean Sea has globally increased by nearly 50 mm, mainly because of a decrease in precipitation over this 15-yr period.

Estimating the Duration of a Case When the Surgeon Has Not Recently Scheduled the Procedure at the Surgical Suite

For some scheduled cases, there may be no previous cases of the same procedure type by the same surgeon for use in estimating the duration of the new case. We evaluated which of 16 different methods of analysis of other surgeons' cases of the same procedure type resulted in the most accurate prediction of the duration of the case that the surgeon had not recently scheduled. We analyzed durations for 4,955 cases, from an operating room information system, for which a surgeon had only scheduled the procedure once, and for which other surgeons had scheduled that same procedure one or more times. Using these data, we determined the difference between the actual duration of the new case and the estimated duration of the new case as calculated by each of the methods (average absolute error of 1.1 h with average case duration of 3.1 h). When no recent historical time data are available for a surgeon doing a given procedure, the mean of the durations of cases of the same scheduled procedure performed by other surgeons is as accurate an estimate as more sophisticated analyses. More research is needed to improve the precision of estimates of case durations.

Dynamic entry deterrence in the UK pathology services market

This paper describes work on a dynamic model of entry deterrence applied to the UK National Health Service (NHS) market for pathology services. The model, based on a game theoretical framework, is concerned with decision support applications. Presented in this paper is a case study analysis of a geographical region in which a provider of pathology services is concerned at the prospect of being exposed to competition from a new entrant. The incumbent provider may undertake strategic investments to create a stock of knowledge and goodwill with the intention of dissuading others from entering the market. The effect of a new entrant is modelled as perturbation of a pre-existing stable Nash-Cournot equilibrium in an oligopolistic market, and is influenced by market forces subject to Government regulation. The original contribution of this study is to identify the nature of these potential strategic investments and their interaction with cash flows. Recent historical data and managerial analysis are used to characterise market growth. An estimate of the incumbent provider's market share which is at risk can be found by examining the local geographical distribution of providers and purchasers of pathology services. On the basis of this analysis we propose a method for obtaining the strategic investment profile which minimises the total investment required to deter entry.

Approaches for Determining Effects of Pollution on Fish Populations of Puget Sound

Puget Sound is a large marine and estuarine ecosystem in Washington State that serves as the habitat for a number of recreationally and commercially important species of groundfish and Pacific salmon Onchorhynchus spp. Over the past several decades, the human population of the Puget Sound drainage basin has increased substantially, resulting in increased habitat degradation and chemical pollution. There is now a body of evidence showing that groundfish and salmon in Puget Sound are experiencing a range of biological effects from chemical contaminant exposure, including impairment of several stages in the reproductive process, increased susceptibility to pathogens resulting from altered immune competence, and development of toxicopathic diseases. Preliminary studies suggest the potential for reduced survival of fish from urban areas of Puget Sound resulting from increased infectious and idiopathic diseases. The question that now must be addressed is whether contaminant-related reductions in reproductive and survival rates are sufficient to affect fish abundance in Puget Sound. In the current study, the potential impact of contaminant-related mortality and reproductive impairment on the population growth rate of English sole Pleuronectes vetulus was examined by simulation modeling. An initial Leslie matrix population model was constructed for investigation of contaminant effects. The adult mortality rate for English sole in Puget Sound was estimated from recent historical data. Age-specific fecundity was determined from previously collected English sole ovary samples. Existing data on the effects of contaminants on reproduction, including impaired gonadal development, reduced spawning ability, and decreased egg and larval viability, were incorporated into the fecundity component of the model. The influence of density-dependent population regulation on model results was also examined. Results suggest that declines in the fecundity component of the model, like those observed in field studies of fish from contaminated sites such as the Duwamish Waterway and Eagle Harbor, could substantially decrease the population growth rate (r) if density dependence is weak or moderate, Estimated declines in r are comparable in magnitude to those associated with typical levels of commercial fishing pressure, However, a compensation for loss of recruits due to contaminant effects is observed if strong density-dependent population regulation is assumed.

Causality and the structure of Canada's balance of payments: Evidence from time series

Recent historical data on Canada's balance of payments reveals a persistent pattern of current account deficits and capital account surpluses. The theoretical interpretation and significance of this recurrent pattern are controversial issues among economists. The essence of this debate is, in our view, a disagreement of a more fundamental nature concerning the underlying causal relationship between the current and capital accounts. Three different causal viewpoints are identified and discussed. Then, an empirical investigation using both bivariate and multivariate time series analysis is conducted in order to help discriminate among the viewpoints. Our findings strongly suggest a feedback relation between the current and the long-term capital account indicating that unidirectional causal viewpoints are inconsistent with the Canadian experience.

Small Cell Lung Cancer

Quantitation of exposure to tobacco products is useful for any individual smoker, and necessary for epidemiological studies which relate smoking to pathology, or which are concerned with the efficacy of smoking cessation methods. The medical history, trying to quantitate the current mean daily cigarette consumption (consumption rate), the cumulative risk (pack years) and the various types of smoking, including inhalation habits, should also be attempted. However, due to the quasi-systematic underrating of tobacco consumption which smokers have revealed on many occasions, together with difficulty in correctly observing cigarette smoking, objective validation of recent historical data by quantitative measurement of tobacco products in tissue fluids is mandatory. Measurements of nicotine and cotinine levels in serum and urine require elaborate and expensive methods, and are not adequate for validation of smoking cessation in smokers who are using nicotine chewing gum. Carbon monoxide is a good marker of smoke inhalation. Normal carboxyhaemoglobin levels allow us to confirm that a subject has recently stopped smoking, as its half-life is only a few hours in blood. Salivary (or plasma) measurements of thiocyanate discriminate between smokers and ex-smokers, with a high probability, particularly in those who have stopped smoking for at least 14 days, separating these clearly from current smokers. However, several potential causes of error must be considered to allow correct interpretation of measurements of thiocyanate.

Technology and U.S. Corn Yields: Plateaus and Price Responsiveness

Corn yields in the United States have increased at a slower rate during the 1970s than in the previous two decades. Fitting straight lines to aggregate corn yields over the period 1954-80 (figure 1) suggests a curvilinear relationship. Different slopes are obtained by splitting the sample at any one of the years 1969, 1970, 1971. For the split shown in figure 1, the slope is 2.67 for 1954-70 and 1.34 for 197180. Since 1970, events have caused corn yields to drop--the 1970 corn blight, drought in 1974 and 1980, and drops in nitrogen application rates in 1974 and 1975. Whether the slowdown in corn yield increases is temporary, permanent, or signals a plateauing of U.S. corn yields is not clear (Swanson and Nyankori). To analyze this issue, the recent historical data (1954-80) on U.S. corn yields is examined. Swanson cautioned against extrapolating past trends into the future without decomposing technology into its components. Multicollinearity problems dictate a limited decomposition into nitrogen and nonnitrogen components. The basis for this distinction is found in microagronomic data. A second objective is to check whether developments over the last decade have significantly changed the elasticity of U.S. corn yields with respect to the fertilizer-corn price ratio.

Measurement Errors and Uncertainty in Parameter Estimates for Stock and Recruitment

A procedure is developed for estimating stock and recruitment parameters in the presence of measurement errors. It requires an independent assessment of the ratio of environmental and measurement error variances, and provides maximum likelihood estimates of the time series of errors as well as the average stock–recruit parameters. Measures of parameter uncertainty are also provided and are incorporated into an analysis of optimum spawning stocks. This analysis indicates that much higher, or at least more variable, spawning runs should be allowed in many Pacific salmon stocks. An immediate need in salmon management is to obtain estimates of the measurement error variance, so that recent historical data can be made more useful.Key words: statistics, stock recruitment, optimum spawning, uncertainty

Tree-ring evidence of past climatic variability

The increasingly visible impact of climatic variability on human affairs lends a sense of urgency to the task of better understanding the workings of the Earth's climatic system. Actual instrumental observations of climate are relatively short, and we must therefore turn to other sources for information about past climates to help develop and test the models that may enable us to predict climatic anomalies such as prolonged droughts or a series of severe winters. Tree -rings are one of the best sources of climatic proxy information. They can provide long, accurately dated, year-by-year records at many points around the globe, and bridge the gap between recent instrumental or historical data and the longer but more generalised geological records. Variations in the width of annual rings reflect the influence of climatic factors that limit the biological processes governing ring formation within a tree. Study of reconstructions of long records of a variety of climatic and related variables, such as temperature, precipitation, stream runoff and barometric pressure over periods of several hundred to several thousand years strongly suggests that the climate of the past century or so is not representative of the conditions that have frequently prevailed over long periods. Proxy records are thus a great help in our efforts to anticipate or predict future climate, which may be significantly different from the recent climatic past.