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A tool for deterministic and probabilistic sensitivity analysis of epidemiologic studies AgEcon
Orsini, Nicola; Bellocco, Rino; Bottai, Matteo; Wolk, Alicja; Greenland, Sander.
Classification errors, selection bias, and uncontrolled confounders are likely to be present in most epidemiologic studies, but the uncertainty introduced by these types of biases is seldom quantified. The authors present a simple yet easy-to-use Stata command to adjust the relative risk for exposure misclassification, selection bias, and an unmeasured confounder. This command implements both deterministic and probabilistic sensitivity analysis. It allows the user to specify a variety of probability distributions for the bias parameters, which are used to simulate distributions for the bias-adjusted exposure–disease relative risk. We illustrate the command by applying it to a case–control study of occupational resin exposure and lung-cancer deaths. By...
Tipo: Article Palavras-chave: Episens; Episensi; Sensitivity analysis; Unmeasured confounder; Misclassification; Bias; Epidemiology; Research Methods/ Statistical Methods.
Ano: 2008 URL: http://purl.umn.edu/120927
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Accuracy, precision and robustness of different methods to obtain samples from silages in fermentation studies R. Bras. Zootec.
Gomes,Rodrigo da Costa; Meyer,Paula Marques; Castro,Ari Luiz de; Saran Netto,Arlindo; Rodrigues,Paulo Henrique Mazza.
The objective of this study was to evaluate accuracy, precision and robustness of two methods to obtain silage samples, in comparison with extraction of liquor by manual screw-press. Wet brewery residue alone or combined with soybean hulls and citrus pulp were ensiled in laboratory silos. Liquor was extracted by a manual screw-press and a 2-mL aliquot was fixed with 0.4 mL formic acid. Two 10-g silage samples from each silo were diluted in 20 mL deionized water or 17% formic acid solution (alternative methods). Aliquots obtained by the three methods were used to determine the silage contents of fermentation end-products. The accuracy of the alternative methods was evaluated by comparing mean bias of estimates obtained by manual screw-press and by...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Bias; Ethanol; Formic acid; Organic acids; Wet brewery residue.
Ano: 2012 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-35982012000600008
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An Empirical Investigation into the Determinants of Trade Policy Bias AgEcon
Hink, Matthew J.; Cardwell, Ryan T.; Lawley, Chad.
There exists an extensive literature that attempts to identify important factors that determine trade policies. An understanding of these important factors could be useful when negotiating trade agreements, especially in agriculture, which is a relatively heavily supported industry. Limao and Panagariya (L&P, 2007) modify Grossman and Helpman’s (G&H, 1994) lobbying model in an attempt to understand why anti-trade bias (as opposed to pro-trade bias, which is predicted by the G&H (1994) model) is the predominant pattern in observed trade policy. L&P (2007) propose that governments seek to reduce inequality between sectors by modifying trade policies in a way that reallocates gross revenue from the larger to the smaller sector. We use measures...
Tipo: Working Paper Palavras-chave: Trade; Policy; Bias; Agricultural and Food Policy; International Relations/Trade.
Ano: 2012 URL: http://purl.umn.edu/122739
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Choosing survey time series for populations as part of an ecosystem approach to fishery management ArchiMer
Trenkel, Verena; Cotter, John.
Ecosystem assessments of fisheries based only on survey data will often have to use surveys that were designed historically for special purposes, e. g. for assessing abundances of two or three target species, or for tuning VPAs. An important question then is whether the previously collected data can provide informative time series of abundance indices and other state indicators for a wider range of target and non-target species. Some potential shortcomings of existing data series are treated in this paper leading to four questions which can guide the user to determine the suitability of an existing time series: did the survey cover the stock of each species adequately? Did survey catchability vary significantly between length or age classes? Did survey...
Tipo: Text Palavras-chave: Bias; Survey based methods; Indicators.
Ano: 2009 URL: http://archimer.ifremer.fr/doc/2009/publication-6900.pdf
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Combining acoustic and CUFES data for the quality control of fish-stock survey estimates ArchiMer
Petitgas, Pierre; Goarant, Anne; Masse, Jacques; Bourriau, Paul.
Petitgas, P., Goarant, A., Masse, J., and Bourriau, P. 2009. Combining acoustic and CUFES data for the quality control of fish-stock survey estimates. - ICES Journal of Marine Science, 66: 1384-1390.
Tipo: Text Palavras-chave: CUFES; Biscay; Bias; Anchovy; Acoustics; Abundance.
Ano: 2009 URL: http://archimer.ifremer.fr/doc/2009/publication-6566.pdf
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Density estimator for strip transects when animals show directional movement and observation speed is slow ArchiMer
Trenkel, Verena.
A strip transect population density estimator and its variance are presented. These take into account stochastic survey velocity as well as stochastic swimming velocity and non-random swimming direction of the surveyed animals. The estimator is mainly of interest for surveys of animals with a directional swimming behaviour and swimming velocities similar to the survey velocity, such as those carried out by divers or remotely operated vehicles.
Tipo: Text Palavras-chave: Variance estimators; Abundance estimation; Bias; Fish movement; Visual transects.
Ano: 2003 URL: http://archimer.ifremer.fr/doc/2003/publication-6655.pdf
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Estimating end effects in trawl catches ArchiMer
Battaglia, Andre; Trenkel, Verena; Rochet, Marie-joelle.
The end effect in trawl catches is defined as the proportion of the fish catch taken during shooting and hauling of the net, a period excluded from that nominally referred to as haul duration. If important, this effect will lead to biased abundance estimates, because the swept area will be underestimated. An experimental survey was carried out to compare catch numbers obtained in standard research 30-min hauls with those from 0-min hauls, the latter referring to the trawl being hauled as soon as the trawl geometry stabilized on the seabed. Average catch ratios (0-min/30-min hauls) ranged from 0.05 (s.d. 0.06) for sole to 0.34 (s.d. 0.64) for hake, indicating that the end effect might be more important and more variable for highly mobile species. As a...
Tipo: Text Palavras-chave: Trawl survey; Bias; Abundance index.
Ano: 2006 URL: https://archimer.ifremer.fr/doc/2006/publication-1686.pdf
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Evaluating uncertainty in measurements of fish shoal aggregate backscattering cross-section caused by small shoal size relative to beam width ArchiMer
Diner, Noel.
The aggregate backscattering cross-section, sag, is the sum of backscattering cross-sections of all fish in a shoal. It is a basic acoustical parameter used for shoal description and biomass estimation. Simulations were undertaken for evaluating the impact of horizontal dimension, density, depth and beam width on measurements of sag for shoals with constant abundance. The important factor determining measurement bias is the ratio of shoal size expressed as along cross-section length relative to along ship beam width at mean shoal depth. The results show that 10 log10(sag) is underestimated by about 8 dB for a 5 m long shoal located at 200 m depth if detected by a 7? beam. A formula for correcting sag estimates for shoal sizes bigger than 1.3 times the beam...
Tipo: Text Palavras-chave: Shoal dimension; Shoal energy; Single beam echosounder; Acoustic measurements; Accuracy; Bias.
Ano: 2007 URL: http://archimer.ifremer.fr/doc/2007/publication-2583.pdf
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Hemólise interfere na mensuração dos biomarcadores plasmáticos de estresse oxidativo em cães Arq. Bras. Med. Vet. Zootec.
Morais,L.; Bosco,A.M.; Baptisttiolli,L.; Torrecilha,R.B.P.; Valadares,T.C.; Hoffmann,D.J.; Ciarlini,P.C..
RESUMO Considerando que, entre todas as fontes de erro analítico, a hemólise é a mais importante na rotina laboratorial, o presente estudo teve como objetivo investigar o efeito da hemólise in vitro sobre os principais biomarcadores plasmáticos de estresse oxidativo mensurados (BPEO) de cães. Para tal, amostras de sangue total de 19 cães clinicamente saudáveis foram hemolisadas em diferentes graus por ação mecânica. Amostras controle contendo baixa concentração de hemoglobina (Hb) no plasma foram comparadas com quatro graus de hemólise (<0,36; 0,36-0,60; 0,61-1,0; 1,1-4g/L Hb). Imediatamente após a hemólise, foram mensuradas as concentrações plasmáticas de ácido úrico (AU), albumina, bilirrubina, gamaglutamiltransferase (GGT), capacidade antioxidante...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Antioxidante; Bias; Erro analítico; Hemoglobina; Oxidante.
Ano: 2018 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0102-09352018000300713
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Humpback whale Megaptera novaeangliae (Cetartiodactyla: Balaenopteridae) group sizes in line transect ship surveys: An evaluation of observer errors Rev. Bras. Zool.
Bortolotto,Guilherme A.; Danilewicz,Daniel; Andriolo,Artur; Zerbini,Alexandre N..
ABSTRACT Accurate estimates of group sizes through line transect sampling methods are important to correctly ascertain the abundance of animals that occur in groups. Since the average observed group size is a component of the distance sampling formula, bias in these data leads to biased abundance estimates. This study aimed to evaluate the potential errors in group size estimation during line transect ship surveys to estimate abundances of the humpback whale, Megaptera novaeangliae (Borowski 1781). In a research cruise along the Brazilian coast, an experiment to collect group size information was conducted from two different sighting platforms on the same vessel. Group sizes were recorded by primary observers at first sighting (PO1) and, in some cases,...
Tipo: Info:eu-repo/semantics/other Palavras-chave: Abundance; Bias; Conservation; Distance sampling; Mysticetus.
Ano: 2016 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1984-46702016000204001
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Production function estimation in Stata using the Olley and Pakes method AgEcon
Yasar, Mahmut; Raciborski, Rafal; Poi, Brian P..
Productivity is often computed by approximating the weighted sum of the inputs from the estimation of the Cobb–Douglas production function. Such estimates, however, may suffer from simultaneity and selection biases. Olley and Pakes (1996, Econometrica 64: 1263–1297) introduced a semiparametric method that allows us to estimate the production function parameters consistently and thus obtain reliable productivity measures by controlling for such biases. This study first reviews this method and then introduces a Stata command to implement it. We show that when simultaneity and selection biases are not controlled for, the coefficients for the variable inputs are biased upward and the coefficients for the fixed inputs are biased downward.
Tipo: Article Palavras-chave: Opreg; Levpet; Production function; Bias; Simultaneity; Research Methods/ Statistical Methods.
Ano: 2008 URL: http://purl.umn.edu/122587
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The Impacts of Attribute Level Framing and Changing Cost Levels on Choice Experiments Value Estimates AgEcon
Kragt, Marit Ellen; Bennett, Jeffrey W..
Choice Experiments (CE) are increasingly used to estimate the values of environmental goods and services. CE questionnaires represent the environmental good under valuation by varying levels of non-market attributes. Inclusion of a cost attribute enables the estimation of monetary values for changes in the non-market attributes presented. The ways in which the levels of the attributes are described in the survey - the ‘attribute frame’ - may affect respondents’ choices. Furthermore, varying levels of the cost attribute may impact CE value estimates. The challenge for CE practitioners is to identify the ‘appropriate’ attribute frames and cost levels. In this paper, the impacts of changing cost levels and the impacts of describing non-market attributes as...
Tipo: Conference Paper or Presentation Palavras-chave: Choice Experiments; Environmental Valuation; Bias; Tasmania; Environmental Economics and Policy.
Ano: 2010 URL: http://purl.umn.edu/59091
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The sampling bias in multi-agent simulation models AgEcon
Buysse, Jeroen; Frija, Aymen; Van der Straeten, Bart; Nolte, Stephan; Lauwers, Ludwig H.; Claeys, Dakerlia; Van Huylenbroeck, Guido.
For practical considerations, it is in some case impossible to simulate MAS models at population level. The current paper shows that MAS models applied to samples with heterogeneous costs of interactions between agents have biased results. Heterogeneous costs of interactions in MAS models can come from the spatial dimension in MAS models or from fixed costs per interaction. The paper presents two correction procedures to remove the sampling bias and to increase the reliability of the outcome. The correction procedures can be very promising for future applications of MAS models because it becomes possible to deploy more complex models without bias on more detailed datasets that are only available at sample level, which will be the case for country- or...
Tipo: Conference Paper or Presentation Palavras-chave: MAS; Bias; Correction; Resampling; Agricultural and Food Policy; Q12; Q18; Q51; Q52.
Ano: 2011 URL: http://purl.umn.edu/99599
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