Invalid estimates of rate of population increase from Glossina (Diptera: Glossinidae) age distributions

1988 ◽  
Vol 78 (1) ◽  
pp. 155-161 ◽  
Author(s):  
J. Van Sickle
Keyword(s):  
Sampling Error ◽  
Age Distribution ◽  
Population Increase ◽  
Sampling Errors ◽  
True Rate ◽  
Survivorship Curve ◽  
A Value ◽  
Tsetse Population ◽  
Rate Of Increase ◽  
Highly Sensitive

AbstractSeveral published reports have presented estimates of the rate of increase, r, based on sampled ovarian age distributions from Glossina populations throughout Africa. These estimates are invalid, because an age distribution sampled at one point in time can be equated to a survivorship curve only if r = 0. When such a survivorship curve and a corresponding fecundity schedule are then used to estimate r via the Euler-Lotka equation, the result is a value of r near zero, regardless of the population's true rate of increase. Synthetic sampling from a hypothetical tsetse population confirmed that estimates computed in this fashion are entirely the products of sampling error. Valid estimates of r can sometimes be obtained from an age distribution, using an alternative method, but such estimates are highly sensitive to sampling errors in the distribution.

Frequency distribution of Wuchereria bancrofti microfilariae in human populations and its relationships with age and sex

Parasitology ◽  
1990 ◽  
Vol 101 (3) ◽  
pp. 429-434 ◽  
Author(s):  
P. K. Das ◽  
A. Manoharan ◽  
A. Srividya ◽  
B. T. Grenfell ◽  
D. A. P. Bundy ◽  
...  
Keyword(s):  
Frequency Distribution ◽  
Negative Binomial ◽  
Age Distribution ◽  
Indirect Evidence ◽  
Wuchereria Bancrofti ◽  
Parameter Estimates ◽  
Human Populations ◽  
Sampling Errors ◽  
Frequency Distributions ◽  
Age And Sex

SUMMARYThis paper examines the effects of host age and sex on the frequency distribution of Wuchereria bancrofti infections in the human host. Microfilarial counts from a large data base on the epidemiology of bancroftian filariasis in Pondicherry, South India are analysed. Frequency distributions of microfilarial counts divided by age are successfully described by zero-truncated negative binomial distributions, fitted by maximum likelihood. Parameter estimates from the fits indicate a significant trend of decreasing overdispersion with age in the distributions above age 10; this pattern provides indirect evidence for the operation of density-dependent constraints on microfilarial intensity. The analysis also provides estimates of the proportion of mf-positive individuals who are identified as negative due to sampling errors (around 5% of the total negatives). This allows the construction of corrected mf age–prevalence curves, which indicate that the observed prevalence may underestimate the true figures by between 25% and 100%. The age distribution of mf-negative individuals in the population is discussed in terms of current hypotheses about the interaction between disease and infection.

scholarly journals The Delta Variant Had Negligible Impact on COVID-19 Vaccine Effectiveness in the USA

2021 ◽  
Author(s):  
Ben Blaiszik ◽  
Carlo Graziani ◽  
James L. Olds ◽  
Ian Foster
Keyword(s):  
Age Distribution ◽  
Vaccine Effectiveness ◽  
Vaccination Status ◽  
Rt Pcr ◽  
Factors Affecting ◽  
A Value ◽  
Health Authorities ◽  
Public Health Authorities ◽  
The Usa ◽  
Zero Baseline

The SARS-CoV-2 Delta variant (B.1.617.2) was initially identified in India in December 2020. Due to its high transmissibility, its prevalence in the U.S.A. grew from a near-zero baseline in early May 2021 to nearly 100% by late August 2021, according to CDC tracking. We accessed openly available data sources from the public health authorities of seven U.S. states, five U.S. counties, and the District of Columbia on RT-PCR COVID-19 tests split by the COVID-19 vaccination status of individuals tested during this period. Together, these time series enable estimation and tracking of COVID-19 vaccine effectiveness (VE∗) (against RT-PCR diagnosed infection) concurrently with the growth of Delta variant prevalence in those locations. Our analyses reveal that in each locality the VE∗ for the combined set of all three US vaccines remained relatively stable and quite well-performing, despite the dramatic concurrent rise of Delta variant prevalence. We conclude that the Delta variant does not significantly evade vaccine-induced immunity. The variations in our measured VE∗ appear to be driven by demographic factors affecting the composition of the vaccinated cohorts, particularly as pertains to age distribution. We report that the measured VE∗, aggregated across the collected sites, began at a value of about 0.9 in mid-May, declined to about 0.76 by mid-July, and recovered to about 0.9 by mid-September.SummaryWe estimated local COVID-19 vaccine effectiveness using RT-PCR COVID-19 test data broken out by vaccination status from select localities in the U.S.A. between 15 May and 15 September 2021 while the SARS-CoV-2 Delta variant (B.1.617.2) was ascending from essentially zero prevalence to total dominance of the genome, and showed that the rise of the Delta variant had negligible effect on vaccine effectiveness.

Counting blood cells of chickens

1959 ◽  
Vol 52 (2) ◽  
pp. 263-272 ◽  
Author(s):  
L. G. Chubb ◽  
J. G. Rowell
Keyword(s):  
Blood Cells ◽  
Leucocyte Count ◽  
Methyl Violet ◽  
Erythrocyte Count ◽  
Standard Errors ◽  
Sampling Errors ◽  
Rate Of Increase ◽  
Blood Smears ◽  
Satisfactory Method ◽  
Good Differentiation

1. Six methods of diluting chicken's blood prior to counting erythrocytes and leucocytes in haemacytometers have been studied. No difficulty is found in recognizing erythrocytes. The most satisfactory method of counting leucocytes was the method described by Natt & Herrick (1952) in which the diluent contains methyl violet. Formulae are given which enable standard errors of estimates to be calculated.2. Three methods of staining blood smears for the differentiation of the various leucocytes have been studied. The method using Leishman's stain appeared to result in good differentiation and was simple to use. However, an experiment to study sampling errors has shown that there may be considerable differences between observers in the percentages of lymphocytes and heterophils when the latter are high, showing that the estimates of these quantities may be biassed. These differences may have been caused by a tendency for heterophils to concentrate to the edges of the smears and for the observers to select different fields for their counts.3. Although blood counts varied only slightly during the day, there were considerable differences from day to day. The average erythrocyte count for ten chickens fluctuated between about 2·9 and 3·5 millions per mm.3 during the first 3 weeks after hatching and was more steady for the next 4 weeks at about 2·9 millions per mm.3. The average leucocyte count rose from about 10,000 to 35,000 per mm.3 during the first 7 weeks of life, the rate of increase being greatest when the chickens were youngest; the rise was mainly due to a rise in the number of lymphocytes.4. There were also considerable differences in blood counts between chickens even though environmental and genetic conditions were standardized as far as possible.

Potential Rates of Increase of a Harbour Porpoise (Phocoena phocoena) Population Subjected to Incidental Mortality in Commercial Fisheries

1991 ◽  
Vol 48 (12) ◽  
pp. 2429-2435 ◽  
Author(s):  
Thomas H. Woodley ◽  
Andrew J. Read
Keyword(s):  
Gulf Of Maine ◽  
Intrinsic Rate ◽  
Frequency Equation ◽  
Harbour Porpoise ◽  
Population Increase ◽  
Intrinsic Rate Of Increase ◽  
Natural Mortality ◽  
Phocoena Phocoena ◽  
Rate Of Increase ◽  
Incidental Mortality

We estimated the potential intrinsic rate of increase (r) of the harbour porpoise (Phocoena phocoena) population in the Bay of Fundy and Gulf of Maine using empirical data on reproductive rates (mx) and several hypothetical survival (Ix) schedules. Schedules of Ix, to maximum ages of 12 and 15 yr, were calculated from two potential natural mortality (nx) schedules combined with several schedules of incidental mortality (hx) estimates. The most realistic results were obtained when nx of non-calves were calculated from Caugley's (1966. Ecology 47: 906–918) smoothed age-frequency equation for Himalayan thar (Hemitragus jemlahicus) and applied in conjunction with a range of calf natural mortality estimates, this model indicates that harbour porpoises have a limited capacity for population increase, and populations are unlikely to sustain even moderate levels of incidental mortality (4% of the population per year). Extending the maximum age used in the models from 12 to 15 yr does little to increase estimates of r for the harbour porpoise population, and hence their susceptibility to incidental mortality.

Sampling Error Correction Evaluated Using a Convective-Scale 1000-Member Ensemble

2019 ◽  
Vol 148 (3) ◽  
pp. 1229-1249 ◽  
Author(s):  
Tobias Necker ◽  
Martin Weissmann ◽  
Yvonne Ruckstuhl ◽  
Jeffrey Anderson ◽  
Takemasa Miyoshi
Keyword(s):  
Sensitivity Analysis ◽  
Data Assimilation ◽  
Error Correction ◽  
Degrees Of Freedom ◽  
Sampling Error ◽  
Lookup Table ◽  
Ensemble Prediction ◽  
Sampling Errors ◽  
Convective Scale ◽  
The Impact

Abstract State-of-the-art ensemble prediction systems usually provide ensembles with only 20–250 members for estimating the uncertainty of the forecast and its spatial and spatiotemporal covariance. Given that the degrees of freedom of atmospheric models are several magnitudes higher, the estimates are therefore substantially affected by sampling errors. For error covariances, spurious correlations lead to random sampling errors, but also a systematic overestimation of the correlation. A common approach to mitigate the impact of sampling errors for data assimilation is to localize correlations. However, this is a challenging task given that physical correlations in the atmosphere can extend over long distances. Besides data assimilation, sampling errors pose an issue for the investigation of spatiotemporal correlations using ensemble sensitivity analysis. Our study evaluates a statistical approach for correcting sampling errors. The applied sampling error correction is a lookup table–based approach and therefore computationally very efficient. We show that this approach substantially improves both the estimates of spatial correlations for data assimilation as well as spatiotemporal correlations for ensemble sensitivity analysis. The evaluation is performed using the first convective-scale 1000-member ensemble simulation for central Europe. Correlations of the 1000-member ensemble forecast serve as truth to assess the performance of the sampling error correction for smaller subsets of the full ensemble. The sampling error correction strongly reduced both random and systematic errors for all evaluated variables, ensemble sizes, and lead times.

scholarly journals Comparison of Field Population Growths of Three Cereal Aphid Species on Winter Wheat

2011 ◽  
Vol 39 (No. 2) ◽  
pp. 61-64 ◽  
Author(s):  
V. Jarošík ◽  
A. Honěk ◽  
A. Tichopád
Keyword(s):  
Winter Wheat ◽  
Rhopalosiphum Padi ◽  
Intrinsic Rate ◽  
Aphid Species ◽  
Population Increase ◽  
Intrinsic Rate Of Increase ◽  
Cereal Aphid ◽  
Metopolophium Dirhodum ◽  
Aphid Density ◽  
Rate Of Increase

Population growths of three aphid species colonising winter wheat stands, Metopolophium dirhodum, Rhopalosiphum padi and Sitobion avenae, were analysed by regression method. The calculations were based on counts in 268 winter wheat plots at 3 or 7 day intervals over 10 (leaves) or 6 (ears) years. The population dynamics of a particular species differed widely between years. Density independent exponential growth of the population was most common, but its rate differed significantly between species, and for S. avenae also between populations on leaves and ears, on which the populations grew fastest. Field estimates of the intrinsic rate of increase derived from the exponential growths ranged between 0.010–0.026 in M. dirhodum, 0.0071–0.011 in R. padi, and between 0.00078–0.0061 and 0.0015–0.13 in S. avenae on leaves and ears, respectively. In the populations with the most vigorous population growth, S. avenae on ears and M. dirhodum on leaves, the rate of population increase significantly decreased with increasing aphid density.  

The Influence of Nitrogen on Dislocation Locking in Float-Zone Silicon

2005 ◽  
Vol 108-109 ◽  
pp. 139-144 ◽  
Author(s):  
John D. Murphy ◽  
A. Giannattasio ◽  
Charles R. Alpass ◽  
Semih Senkader ◽  
Robert J. Falster ◽  
...  
Keyword(s):  
Activation Energy ◽  
Annealing Time ◽  
Nitrogen Concentration ◽  
Dislocation Core ◽  
Float Zone ◽  
A Value ◽  
Rate Of Increase ◽  
Activation Energy For Diffusion ◽  
Nitrogen Concentrations ◽  
Locking Effect

Dislocation locking by nitrogen impurities has been investigated in float-zone silicon with nitrogen concentrations of 2.2 x 1015cm-3 and 3 x 1014cm-3. The stress required to unlock dislocations pinned by nitrogen impurities was measured as a function of annealing time (0 to 2500 hours) and temperature (550 to 830°C). For all conditions investigated the locking effect was found to increase linearly with annealing time before saturating. It is assumed that the rate of increase of unlocking stress with annealing time is a measure of transport of nitrogen to the dislocation core. This rate of increase was found to depend linearly on nitrogen concentration, which is consistent with transport by a dimeric species, whose activation energy for diffusion is approximately 1.4eV. The saturation unlocking stress has been found to be dependent on the nitrogen concentration. Additionally, the temperature dependence of the stress required to move dislocations immobilised by nitrogen impurities has been studied. By assuming a value for the binding energy of the nitrogen to the dislocation, the density of the locking species at the dislocation core has been calculated.

scholarly journals A method to correct sampling ghosts in historic near-infrared Fourier Transform Spectrometer (FTS) measurements

2013 ◽  
Vol 6 (2) ◽  
pp. 3545-3579 ◽  
Author(s):  
S. Dohe ◽  
V. Sherlock ◽  
F. Hase ◽  
M. Gisi ◽  
J. Robinson ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Near Infrared ◽  
Sampling Error ◽  
Total Carbon ◽  
Sampling Errors ◽  
Step Procedure ◽  
Residual Difference ◽  
Correction Scheme ◽  
Parent Ratio ◽  
Good Agreement

Abstract. The Total Carbon Column Observing Network (TCCON) has been established to provide ground-based remote sensing measurements of the column-average dry air mole fractions of key greenhouse gases. To ensure the network wide consistency, biases between Fourier Transform spectrometers at different sites have to be well controlled. In this study we investigate a fundamental correction scheme for errors in the sampling of the interferogram. This is a two-step procedure in which the laser sampling error (LSE) is quantified using a subset of suitable interferograms and then used to resample all the interferograms in the timeseries. Timeseries of measurements acquired at the TCCON sites Izaña and Lauder are used to demonstrate the method. At both sites the sampling error histories show changes in LSE due to instrument interventions. Estimated LSE are in good agreement with sampling errors inferred from lamp measurements of the ghost to parent ratio (Lauder). The LSE introduce retrieval biases which are minimised when the interferograms are resampled. The original timeseries of Xair and XCO2 at both sites show discrepancies of 0.2–0.5% due to changes in the LSE associated with instrument interventions or changes in the measurement sample rate. After resampling discrepancies are reduced to 0.1% at Lauder and 0.2% at Izaña. In the latter case, coincident changes in interferometer alignment may also contribute to the residual difference.

Reducing Instrumentation Errors Caused by Circumferential Flow-Field Variations in Multistage Axial Compressors

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
M. Chilla ◽  
G. Pullan ◽  
S. Gallimore
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Sampling Error ◽  
Leading Edge ◽  
Stagnation Pressure ◽  
Wave Number ◽  
Stagnation Temperature ◽  
Sampling Errors ◽  
Mean Flow ◽  
Axial Compressors

Abstract The effects of blade row interactions on stator-mounted instrumentation in axial compressors are investigated using unsteady numerical calculations. The test compressor is an eight-stage machine representative of an aero-engine core compressor. For the unsteady calculations, a 180-deg sector (half-annulus) model of the compressor is used. It is shown that the time-mean flow field in the stator leading edge planes is circumferentially nonuniform. The circumferential variations in stagnation pressure and stagnation temperature, respectively, reach 4.2% and 1.1% of the local mean. Using spatial wave number analysis, the incoming wakes from the upstream stator rows are identified as the dominant source of the circumferential variations in the front and middle of the compressor, while toward the rear of the compressor, the upstream influence of the eight struts in the exit duct becomes dominant. Based on three circumferential probes, the sampling errors for stagnation pressure and stagnation temperature are calculated as a function of the probe locations. Optimization of the probe locations shows that the sampling error can be reduced by up to 77% by circumferentially redistributing the individual probes. The reductions in the sampling errors translate to reductions in the uncertainties of the overall compressor efficiency and inlet flow capacity by up to 50%. Recognizing that data from large-scale unsteady calculations are rarely available in the instrumentation phase for a new test rig or engine, a method for approximating the circumferential variations with single harmonics is presented. The construction of the harmonics is based solely on the knowledge of the number of stators in each row and a small number of equispaced probes. It is shown how excursions in the sampling error are reduced by increasing the number of circumferential probes.

Probabilistic Analysis of List Data for the Estimation of Extreme Design Loads for Wind Turbine Components

2003 ◽  
Author(s):  
M. D. Pandey ◽  
H. J. Sutherland
Keyword(s):  
Wind Turbine ◽  
Sampling Error ◽  
Field Measurements ◽  
Structural Data ◽  
Value Theory ◽  
Extreme Value ◽  
Sampling Errors ◽  
Extreme Loads ◽  
Mean Wind Speed ◽  
Design Loads

Robust estimation of wind turbine design loads for service lifetimes of 30 to 50 years that are based on field measurements of a few days is a challenging problem. Estimating the long-term load distribution involves the integration of conditional distributions of extreme loads over the mean wind speed and turbulence intensity distributions. However, the accuracy of the statistical extrapolation is fairly sensitive to both model and sampling errors. Using measured inflow and structural data from the LIST program, this paper presents a comparative assessment of extreme loads using three distributions: namely, the Gumbel, Weibull and Generalized Extreme Value distributions. The paper uses L-moments, in place of traditional product moments, to reduce the sampling error. The paper discusses the application of extreme value theory and highlights its practical limitations. The proposed technique has the potential of improving estimates of the design loads for wind turbines.

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