Application to Biased Sampling Problems

2021 ◽  
pp. 107-134
Author(s):  
Hua Yun Chen
Keyword(s):  
Biased Sampling ◽  
Sampling Problems

Managing Heterogeneity of Variance in Studies of Reliability Generalization With Alpha Coefficients

Methodology ◽  
2012 ◽  
Vol 8 (2) ◽  
pp. 71-80 ◽  
Author(s):  
Juan Botella ◽  
Manuel Suero
Keyword(s):  
Reliability Estimation ◽  
Biased Sampling ◽  
Reliability Generalization ◽  
Alpha Coefficient ◽  
Range Restriction ◽  
Sampling Schemes ◽  
Cronbach's Alpha ◽  
Heterogeneous Variances ◽  
Heterogeneity Of Variance ◽  
Meta Analyses

In Reliability Generalization (RG) meta-analyses, the importance of bearing in mind the problems of range restriction or biased sampling and their influence on reliability estimation has often been highlighted. Nevertheless, the presence of heterogeneous variances in the included studies has been diagnosed in a subjective way and has not been taken into account in later analyses. Procedures to detect the presence of a variety of sampling schemes and to manage them in the analyses are proposed. The procedures are further explained with an example, by applying them to 25 estimates of Cronbach’s alpha coefficient in the Hamilton Scale for Depression.

Overcoming Gas Sampling Problems: Analysis of Volatiles Using Capillary Column Needles

HortScience ◽  
1996 ◽  
Vol 31 (4) ◽  
pp. 643f-643
Author(s):  
Weimin Deng ◽  
Randolph M. Beaudry
Keyword(s):  
Stainless Steel ◽  
Capillary Column ◽  
Dependent Manner ◽  
Stainless Steel Capillary ◽  
Stainless Steel Needle ◽  
Injection Volume ◽  
Volatile Analysis ◽  
Gas Tight ◽  
Sampling Problems ◽  
Time Injection

Sampling factors that could affect gas chromatograph (GC) response for volatile analysis such as syringe pumping time, injection volume, needle length, temperature, and the type of volatile were investigated. Capillary GC column segments (steel and glass) were installed in gas-tight syringes and used as needles for volatile analysis. Standard stainless-steel needles were also used. Hexylacetate, ethyl-2-methylbutyrate, 6-methyl-5-hepten-2-one, and butanol standard were measured. The number of pumps required to maximize GC response for each needle–volatile combination was determined. Maximal GC response for hexylacetate using standard stainless steel, capillary glass, and capillary steel needles required 10, 20 and 30 pumps, respectively. However, for butanol measurement, the optimal syringe pump number was 5 to 10 for all needle types. The use of a capillary needle resulted in an increase in GC response in the range of 3- to 15-fold relative to a standard stainless steel needle. Injection volume affected GC response in a needle-and volatile-dependent manner. In no case did injection volume vs. GC response extrapolate through origin. The GC response for capillary column needles increased as temperature decreased. Capillary column needles may be useful tools for analysis of volatiles that readily partition into the column coating.

scholarly journals Do We Need to Use Bats as Bioindicators?

Biology ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 693
Author(s):  
Danilo Russo ◽  
Valeria B. Salinas-Ramos ◽  
Luca Cistrone ◽  
Sonia Smeraldo ◽  
Luciano Bosso ◽  
...  
Keyword(s):  
Scientific Evidence ◽  
Legal Obligation ◽  
Farming Practices ◽  
Population Declines ◽  
Technological Advances ◽  
River Quality ◽  
Surrogate Taxa ◽  
Available Information ◽  
Sampling Problems ◽  
The Eu

Bats show responses to anthropogenic stressors linked to changes in other ecosystem components such as insects, and as K-selected mammals, exhibit fast population declines. This speciose, widespread mammal group shows an impressive trophic diversity and provides key ecosystem services. For these and other reasons, bats might act as suitable bioindicators in many environmental contexts. However, few studies have explicitly tested this potential, and in some cases, stating that bats are useful bioindicators more closely resembles a slogan to support conservation than a well-grounded piece of scientific evidence. Here, we review the available information and highlight the limitations that arise in using bats as bioindicators. Based on the limited number of studies available, the use of bats as bioindicators is highly promising and warrants further investigation in specific contexts such as river quality, urbanisation, farming practices, forestry, bioaccumulation, and climate change. Whether bats may also serve as surrogate taxa remains a controversial yet highly interesting matter. Some limitations to using bats as bioindicators include taxonomical issues, sampling problems, difficulties in associating responses with specific stressors, and geographically biased or delayed responses. Overall, we urge the scientific community to test bat responses to specific stressors in selected ecosystem types and develop research networks to explore the geographic consistency of such responses. The high cost of sampling equipment (ultrasound detectors) is being greatly reduced by technological advances, and the legal obligation to monitor bat populations already existing in many countries such as those in the EU offers an important opportunity to accomplish two objectives (conservation and bioindication) with one action.

scholarly journals Gibbs partitions, Riemann–Liouville fractional operators, Mittag–Leffler functions, and fragmentations derived from stable subordinators

2021 ◽  
Vol 58 (2) ◽  
pp. 314-334
Author(s):  
Man-Wai Ho ◽  
Lancelot F. James ◽  
John W. Lau
Keyword(s):  
Special Functions ◽  
Dirichlet Distribution ◽  
Random Trees ◽  
Fractional Integrals ◽  
Biased Sampling ◽  
Scaling Limits ◽  
Fractional Operators ◽  
Random Partitions ◽  
Two Parameter ◽  
Potential Use

AbstractPitman (2003), and subsequently Gnedin and Pitman (2006), showed that a large class of random partitions of the integers derived from a stable subordinator of index $\alpha\in(0,1)$ have infinite Gibbs (product) structure as a characterizing feature. The most notable case are random partitions derived from the two-parameter Poisson–Dirichlet distribution, $\textrm{PD}(\alpha,\theta)$, whose corresponding $\alpha$-diversity/local time have generalized Mittag–Leffler distributions, denoted by $\textrm{ML}(\alpha,\theta)$. Our aim in this work is to provide indications on the utility of the wider class of Gibbs partitions as it relates to a study of Riemann–Liouville fractional integrals and size-biased sampling, and in decompositions of special functions, and its potential use in the understanding of various constructions of more exotic processes. We provide characterizations of general laws associated with nested families of $\textrm{PD}(\alpha,\theta)$ mass partitions that are constructed from fragmentation operations described in Dong et al. (2014). These operations are known to be related in distribution to various constructions of discrete random trees/graphs in [n], and their scaling limits. A centerpiece of our work is results related to Mittag–Leffler functions, which play a key role in fractional calculus and are otherwise Laplace transforms of the $\textrm{ML}(\alpha,\theta)$ variables. Notably, this leads to an interpretation within the context of $\textrm{PD}(\alpha,\theta)$ laws conditioned on Poisson point process counts over intervals of scaled lengths of the $\alpha$-diversity.

scholarly journals Using excess deaths and testing statistics to determine COVID-19 mortalities

2021 ◽  
Author(s):  
Lucas Böttcher ◽  
Maria R. D’Orsogna ◽  
Tom Chou
Keyword(s):  
New York ◽  
New York City ◽  
Disease Prevalence ◽  
Statistical Testing ◽  
Biased Sampling ◽  
Mortality Data ◽  
Sir Epidemic Model ◽  
Excess Death ◽  
Sir Epidemic ◽  
Excess Deaths

AbstractFactors such as varied definitions of mortality, uncertainty in disease prevalence, and biased sampling complicate the quantification of fatality during an epidemic. Regardless of the employed fatality measure, the infected population and the number of infection-caused deaths need to be consistently estimated for comparing mortality across regions. We combine historical and current mortality data, a statistical testing model, and an SIR epidemic model, to improve estimation of mortality. We find that the average excess death across the entire US from January 2020 until February 2021 is 9$$\%$$ % higher than the number of reported COVID-19 deaths. In some areas, such as New York City, the number of weekly deaths is about eight times higher than in previous years. Other countries such as Peru, Ecuador, Mexico, and Spain exhibit excess deaths significantly higher than their reported COVID-19 deaths. Conversely, we find statistically insignificant or even negative excess deaths for at least most of 2020 in places such as Germany, Denmark, and Norway.

Some Sampling Problems in Fishery Work

Biometrics ◽  
1971 ◽  
Vol 27 (3) ◽  
pp. 631 ◽  
Author(s):  
Patrick K. Tomlinson
Keyword(s):  
Sampling Problems

scholarly journals Metalloregulator CueR biases RNA polymerase’s kinetic sampling of dead-end or open complex to repress or activate transcription

2015 ◽  
Vol 112 (44) ◽  
pp. 13467-13472 ◽  
Author(s):  
Danya J. Martell ◽  
Chandra P. Joshi ◽  
Ahmed Gaballa ◽  
Ace George Santiago ◽  
Tai-Yen Chen ◽  
...  
Keyword(s):  
Single Molecule ◽  
Transcription Initiation ◽  
Structural Changes ◽  
Dynamic Equilibrium ◽  
Specific Binding ◽  
Binding Mode ◽  
Biased Sampling ◽  
Single Molecule Fret ◽  
Dead End ◽  
The Dead

Metalloregulators respond to metal ions to regulate transcription of metal homeostasis genes. MerR-family metalloregulators act on σ70-dependent suboptimal promoters and operate via a unique DNA distortion mechanism in which both the apo and holo forms of the regulators bind tightly to their operator sequence, distorting DNA structure and leading to transcription repression or activation, respectively. It remains unclear how these metalloregulator−DNA interactions are coupled dynamically to RNA polymerase (RNAP) interactions with DNA for transcription regulation. Using single-molecule FRET, we study how the copper efflux regulator (CueR)—a Cu+-responsive MerR-family metalloregulator—modulates RNAP interactions with CueR’s cognate suboptimal promoter PcopA, and how RNAP affects CueR−PcopAinteractions. We find that RNAP can form two noninterconverting complexes at PcopAin the absence of nucleotides: a dead-end complex and an open complex, constituting a branched interaction pathway that is distinct from the linear pathway prevalent for transcription initiation at optimal promoters. Capitalizing on this branched pathway, CueR operates via a “biased sampling” instead of “dynamic equilibrium shifting” mechanism in regulating transcription initiation; it modulates RNAP’s binding–unbinding kinetics, without allowing interconversions between the dead-end and open complexes. Instead, the apo-repressor form reinforces the dominance of the dead-end complex to repress transcription, and the holo-activator form shifts the interactions toward the open complex to activate transcription. RNAP, in turn, locks CueR binding at PcopAinto its specific binding mode, likely helping amplify the differences between apo- and holo-CueR in imposing DNA structural changes. Therefore, RNAP and CueR work synergistically in regulating transcription.

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