scholarly journals Covid-19 prevalence estimation by random sampling in the wider population - Optimal sample pooling under varying assumptions about true prevalence

2020 ◽  
Author(s):  
Ola Brynildsrud
Keyword(s):  
Confidence Intervals ◽  
Random Sampling ◽  
Large Fraction ◽  
True Prevalence ◽  
Prevalence Estimation ◽  
Optimal Sample ◽  
Wide Range ◽  
Prevalence Estimates ◽  
Test Criteria ◽  
Sample Pooling

ABSTRACTThe number of confirmed Covid-19 cases in a population is used as a coarse measurement for the burden of disease. However, this number depends heavily on the sampling intensity and the various test criteria used in different jurisdictions. A wide range of sources indicate that a large fraction of cases go undetected. Estimates of the true prevalence of Covid-19 can be made by random sampling in the wider population. Here we use simulations to explore confidence intervals of prevalence estimates under different sampling intensities and degrees of sample pooling.

scholarly journals COVID-19 prevalence estimation by random sampling in population - Optimal sample pooling under varying assumptions about true prevalence

2020 ◽  
Author(s):  
Ola Brynildsrud
Keyword(s):  
Random Sampling ◽  
Large Fraction ◽  
Rt Pcr ◽  
Individual Level ◽  
True Prevalence ◽  
Prevalence Estimation ◽  
Prevalence Estimates ◽  
Sample Pooling ◽  
Many Sources ◽  
Low Prevalence

Abstract Background: The number of confirmed COVID-19 cases divided by population size is used as a coarse measurement for the burden of disease in a population. However, this fraction depends heavily on the sampling intensity and the various test criteria used in different jurisdictions, and many sources indicate that a large fraction of cases tend to go undetected. Methods: Estimates of the true prevalence of COVID-19 in a population can be made by random sampling and pooling of RT-PCR tests. Here I use simulations to explore how experiment sample size and degrees of sample pooling impact precision of prevalence estimates and potential for minimizing the total number of tests required to get individual-level diagnostic results.Results: Sample pooling can greatly reduce the total number of tests required for prevalence estimation. In low-prevalence populations, it is theoretically possible to pool hundreds of samples with only marginal loss of precision. Even when the true prevalence is as high as 10% it can be appropriate to pool up to 15 samples. Sample pooling can be particularly beneficial when the test has imperfect specificity by providing more accurate estimates of the prevalence than an equal number of individual-level tests.Conclusion: Sample pooling should be considered in COVID-19 prevalence estimation efforts.

scholarly journals COVID-19 prevalence estimation by random sampling in the population - Optimal sample pooling under varying assumptions about true prevalence

2020 ◽  
Author(s):  
Ola Brynildsrud
Keyword(s):  
Random Sampling ◽  
Large Fraction ◽  
Positive Sample ◽  
Individual Level ◽  
True Prevalence ◽  
Prevalence Estimation ◽  
Optimal Sample ◽  
Sample Pooling ◽  
Many Sources ◽  
The Cost

Abstract Background The number of confirmed COVID-19 cases divided by population size is used as a coarse measurement for the burden of disease in a population. However, this fraction depends heavily on the sampling intensity and the various test criteria used in different jurisdictions, and many sources indicate that a large fraction of cases tend to go undetected. Methods Estimates of the true prevalence of COVID-19 in a population can be made by random sampling. Here I use simulations to explore confidence intervals of prevalence estimates under different sampling strategies, exploring optimal sample sizes and degrees of sample pooling at a range of true prevalence levels. Results Sample pooling can greatly reduce the total number of tests required for prevalence estimation. In low-prevalence populations, it is theoretically possible to pool hundreds of samples with only marginal loss of precision. Even when the true prevalence is as high as 10% it can be appropriate to pool up to 15 samples, although this comes with the cost of not knowing which patients were positive. Sample pooling can be particularly beneficial when the test has imperfect specificity can provide more accurate estimates of the prevalence than an equal number of individual-level tests. Conclusion Sample pooling should be considered in COVID-19 prevalence estimation efforts.

scholarly journals tPRiors: A tool for prior elicitation and obtaining posterior distributions of true disease prevalence

2021 ◽  
Author(s):  
Konstantinos Pateras
Keyword(s):  
Bayesian Methods ◽  
Diagnostic Tests ◽  
False Negative ◽  
Disease Prevalence ◽  
Final Report ◽  
Prior Elicitation ◽  
True Prevalence ◽  
Prevalence Estimation ◽  
Prevalence Estimates ◽  
Multiple Population

Abstract Background: Tests have false positive or false negative results, which, if not properly accounted for, may provide misleading apparent prevalence estimates based on the observed rate of positive tests and not the true disease prevalence estimates. Methods to estimate the true prevalence of disease, adjusting for the sensitivity and the specificity of the diagnostic tests are available and can be applied, though, such procedures can be cumbersome to researchers with or without a solid statistical background.Objective: To create a web-based application that integrates statistical methods for Bayesian inference of true disease prevalence based on prior elicitation for the accuracy of the diagnostic tests. This tool allows practitioners to simultaneously analyse and visualize results while using interactive sliders and output prior/posterior plots.Methods: Three methods for prevalence prior elicitation and four core families of Bayesian methods have been combined and incorporated in this web tool. |tPRiors| user interface has been developed with R and Shiny and may be freely accessed on-line.Results: |tPRiors| allows researchers to use preloaded data or upload their own datasets and perform analysis on either single or multiple population groups clusters), allowing, if needed, for excess zero prevalence. The final report is exported in raw parts either as .rdata or .png files. We utilize a real multiple-population and a toy single-population dataset to demonstrate the robustness and capabilities of |tPRiors|.Conclusions: We expect |tPRiors| to be helpful for researchers interested in true disease prevalence estimation and they are keen on accounting for prior information. |tPRiors| acts both as a statistical tool and a simplified step-by-step statistical framework that facilitates the use of complex Bayesian methods. The application of |tPRiors| is expected to aid standardization of practices in the field of Bayesian modelling on subject and multiple group-based true prevalence estimation.

Personality disorder and intellectual disability – concept and prevalence

2015 ◽  
Vol 9 (4) ◽  
pp. 163-173 ◽  
Author(s):  
Hilde Katrine Andersen
Keyword(s):  
Intellectual Disability ◽  
Personality Disorder ◽  
Design Methodology ◽  
Cross Sectional ◽  
Content Type ◽  
True Prevalence ◽  
Conceptual Clarity ◽  
Wide Range ◽  
Prevalence Estimates

Purpose – The range of prevalence of personality disorder (PD) found in people with intellectual disability (ID) has been reported as vast, and has included data from dissimilar settings. The purpose of this paper is to review the reported prevalence of PD in the general population of people with ID, and to consider how different and changing ideas about PD have affected these rates. Design/methodology/approach – Cross-sectional studies of the prevalence of PD in people with ID were identified. The quality of the studies was considered, along with how cases of PD were identified. Findings – Six studies were included. The reported prevalence of PD in people known to have ID ranged from 0.7 to 35 per cent. Possible reasons for this wide range included different views of PD and methods of assessment. Research limitations/implications – The wide range of findings suggests that methodological differences are significant. Consideration to how clinicians should respond to the overlap of impairment between ID and PD may improve the conceptual clarity of PD, informing future epidemiological research. Originality/value – This review was limited to studies of samples likely to be representative of the general ID population. The range of prevalence estimates was narrower than previously reported, and more likely to reflect the true prevalence rate of PD amongst people who have ID. Consideration was also given to how different ideas of PD led to different methods and may have contributed to variance in the results.

scholarly journals Assessing land–ocean connectivity via submarine groundwater discharge (SGD) in the Ria Formosa Lagoon (Portugal): combining radon measurements and stable isotope hydrology

2016 ◽  
Vol 20 (8) ◽  
pp. 3077-3098 ◽  
Author(s):  
Carlos Rocha ◽  
Cristina Veiga-Pires ◽  
Jan Scholten ◽  
Kay Knoeller ◽  
Darren R. Gröcke ◽  
...  
Keyword(s):  
Submarine Groundwater Discharge ◽  
Large Fraction ◽  
Groundwater Discharge ◽  
Point Sources ◽  
Total N ◽  
Ria Formosa ◽  
Basin Scale ◽  
Wide Range ◽  
Dominant Feature ◽  
Submarine Groundwater

Abstract. Natural radioactive tracer-based assessments of basin-scale submarine groundwater discharge (SGD) are well developed. However, SGD takes place in different modes and the flow and discharge mechanisms involved occur over a wide range of spatial and temporal scales. Quantifying SGD while discriminating its source functions therefore remains a major challenge. However, correctly identifying both the fluid source and composition is critical. When multiple sources of the tracer of interest are present, failure to adequately discriminate between them leads to inaccurate attribution and the resulting uncertainties will affect the reliability of SGD solute loading estimates. This lack of reliability then extends to the closure of local biogeochemical budgets, confusing measures aiming to mitigate pollution.Here, we report a multi-tracer study to identify the sources of SGD, distinguish its component parts and elucidate the mechanisms of their dispersion throughout the Ria Formosa – a seasonally hypersaline lagoon in Portugal. We combine radon budgets that determine the total SGD (meteoric + recirculated seawater) in the system with stable isotopes in water (δ2H, δ18O), to specifically identify SGD source functions and characterize active hydrological pathways in the catchment. Using this approach, SGD in the Ria Formosa could be separated into two modes, a net meteoric water input and another involving no net water transfer, i.e., originating in lagoon water re-circulated through permeable sediments. The former SGD mode is present occasionally on a multi-annual timescale, while the latter is a dominant feature of the system. In the absence of meteoric SGD inputs, seawater recirculation through beach sediments occurs at a rate of  ∼  1.4  ×  106 m3 day−1. This implies that the entire tidal-averaged volume of the lagoon is filtered through local sandy sediments within 100 days ( ∼  3.5 times a year), driving an estimated nitrogen (N) load of  ∼  350 Ton N yr−1 into the system as NO3−. Land-borne SGD could add a further  ∼  61 Ton N yr−1 to the lagoon. The former source is autochthonous, continuous and responsible for a large fraction (59 %) of the estimated total N inputs into the system via non-point sources, while the latter is an occasional allochthonous source capable of driving new production in the system.

scholarly journals Adjusting Coronavirus Prevalence Estimates for Laboratory Test Kit Error

2020 ◽  
Vol 190 (1) ◽  
pp. 109-115 ◽  
Author(s):  
Christopher T Sempos ◽  
Lu Tian
Keyword(s):  
Policy Decisions ◽  
True Prevalence ◽  
Test Kit ◽  
Study Results ◽  
Prevalence Estimates ◽  
Testing Error ◽  
State And Local Government ◽  
State And Local ◽  
Government Rules ◽  
Public Policy Decisions

Abstract Testing representative populations to determine the prevalence or the percentage of the population with active severe acute respiratory syndrome coronavirus 2 infection and/or antibodies to infection is being recommended as essential for making public policy decisions to ease restrictions or to continue enforcing national, state, and local government rules to shelter in place. However, all laboratory tests are imperfect and have estimates of sensitivity and specificity less than 100%—in some cases, considerably less than 100%. That error will lead to biased prevalence estimates. If the true prevalence is low, possibly in the range of 1%–5%, then testing error will lead to a constant background of bias that most likely will be larger, and possibly much larger, than the true prevalence itself. As a result, what is needed is a method for adjusting prevalence estimates for testing error. Methods are outlined in this article for adjusting prevalence estimates for testing error both prospectively in studies being planned and retrospectively in studies that have been conducted. If used, these methods also would help harmonize study results within countries and worldwide. Adjustment can lead to more accurate prevalence estimates and to better policy decisions. However, adjustment will not improve the accuracy of an individual test.

scholarly journals PROSPEK PENINGKATAN KUALITAS KOMPONEN PARIWISATA DI KERATON SURAKARTA

Jurnal IPTA ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 60
Author(s):  
Devi Rusdiana Putri ◽  
Agam Marsoyo
Keyword(s):  
Local Government ◽  
Random Sampling ◽  
Sampling Technique ◽  
Tourist Attractions ◽  
Wide Range ◽  
Component Development ◽  
Component Quality

Surakarta and Yogyakarta Palace are two palaces that historically connected and both are located in the middle of Surakarta dan Yogyakarta region. They offer nearly the same tourist products, but they have significantly different tourist numbers. Whereas, Surakarta Palace itself has various potential tourist attractions to visit. This study aimed to measure quality and define the prospect of tourism component development in Surakarta Palace. This research used questionnaire with random sampling technique which later supported by observation and interview to the parties concerned. This study found out that : (1) the tourism component quality in Surakarta palace is different compared to Yogyakarta palace due the lack of diversity in attractions and limited amenities choices. (2) But Surakarta Palace has wide range of potential that can be well-developed. (3) The support from local government and community have not enough yet to encourage the improvement of tourism component’s quality in Surakarta Palace.

scholarly journals Assessment of the accuracy of different systems for measuring football velocity and spin rate in the field

2019 ◽  
Vol 233 (2) ◽  
pp. 324-330 ◽  
Author(s):  
Katrine Okholm Kryger ◽  
Séan Mitchell ◽  
Steph Forrester
Keyword(s):  
Systematic Error ◽  
Confidence Intervals ◽  
High Speed ◽  
Football Player ◽  
Random Errors ◽  
High Speed Video ◽  
Field Assessment ◽  
Wide Range ◽  
Ball Velocity ◽  
Level Of Agreement

The aim of this study was to measure the level of agreement of four portable football velocity and spin rate measurement systems (Jugs speed radar gun, 2-D high-speed video, TrackMan and adidas miCoach football) against a Vicon motion analysis system. One skilled male university football player performed 70 shots covering a wide range of ball velocities (12–30 m s−1) and spin rates (94–743 r/min). A Bland–Altman analysis was used to assess the level of agreement. For ball velocity, the 2-D high-speed video had the smallest systematic error, followed by the radar gun, TrackMan and miCoach football at 0.2, 0.4, 0.5 and 4.8 m s−1, respectively. A similar ranking was also observed for the random errors (95% confidence intervals: ±0.4, ±1.5, ±1.9 and ±6.0 m s−1). The first three systems all tracked ball velocity in >90% of shots, while the miCoach football tracked slightly fewer shots (79%). For spin rate, the miCoach football had a much smaller systematic error (4 vs 38 r/min) and random error (95% confidence intervals: ±24 vs ±355 r/min) compared to TrackMan. The miCoach also successfully tracked spin rate in more shots than the TrackMan (79% vs 44%). These results indicate that 2-D high-speed video would be the preferred option for the field assessment of ball velocity; however, radar gun and TrackMan may also be appropriate. A minimum of 10 frames of 2-D high-speed video, captured close to the ball starting position, was demonstrated to be sufficient in providing a reliable measure of ball velocity. The miCoach ball is the preferred option for field assessment of ball spin rate.

scholarly journals Investigation on Blending Effects of Gasoline Fuel with N-Butanol, DMF, and Ethanol on the Fuel Consumption and Harmful Emissions in a GDI Vehicle

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1845 ◽  
Author(s):  
Haifeng Liu ◽  
Xichang Wang ◽  
Diping Zhang ◽  
Fang Dong ◽  
Xinlu Liu ◽  
...  
Keyword(s):  
Steady State ◽  
Fuel Consumption ◽  
Large Fraction ◽  
Direct Injection ◽  
Transient State ◽  
Gasoline Direct Injection ◽  
Nox Emissions ◽  
Fuel Blends ◽  
Wide Range ◽  
Oxygenated Fuel

The effects of three kinds of oxygenated fuel blends—i.e., ethanol-gasoline, n-butanol-gasoline, and 2,5-dimethylfuran (DMF)-gasoline-on fuel consumption, emissions, and acceleration performance were investigated in a passenger car with a chassis dynamometer. The engine mounted in the vehicle was a four-cylinder, four-stroke, turbocharging gasoline direct injection (GDI) engine with a displacement of 1.395 L. The test fuels include ethanol-gasoline, n-butanol-gasoline, and DMF-gasoline with four blending ratios of 20%, 50%, 75%, and 100%, and pure gasoline was also tested for comparison. The original contribution of this article is to systemically study the steady-state, transient-state, cold-start, and acceleration performance of the tested fuels under a wide range of blending ratios, especially at high blending ratios. It provides new insight and knowledge of the emission alleviation technique in terms of tailoring the biofuels in GDI turbocharged engines. The results of our works showed that operation with ethanol–gasoline, n-butanol–gasoline, and DMF–gasoline at high blending ratios could be realized in the GDI vehicle without any modification to its engine and the control system at the steady state. At steady-state operation, as compared with pure gasoline, the results indicated that blending n-butanol could reduce CO2, CO, total hydrocarbon (THC), and NOX emissions, which were also decreased by employing a higher blending ratio of n-butanol. However, a high fraction of n-butanol increased the volumetric fuel consumption, and so did the DMF–gasoline and ethanol–gasoline blends. A large fraction of DMF reduced THC emissions, but increased CO2 and NOX emissions. Blending n-butanol can improve the equivalent fuel consumption. Moreover, the particle number (PN) emissions were significantly decreased when using the high blending ratios of the three kinds of oxygenated fuels. According to the results of the New European Drive Cycle (NEDC) cycle, blending 20% of n-butanol with gasoline decreased CO2 emissions by 5.7% compared with pure gasoline and simultaneously reduced CO, THC, NOX emissions, while blending ethanol only reduced NOX emissions. PN and particulate matter (PM) emissions decreased significantly in all stages of the NEDC cycle with the oxygenated fuel blends; the highest reduction ratio in PN was 72.87% upon blending 20% ethanol at the NEDC cycle. The high proportion of n-butanol and DMF improved the acceleration performance of the vehicle.

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