scholarly journals Improving A/B Testing on the Basis of Possibilistic Reward Methods: A Numerical Analysis

Symmetry ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 2175
Author(s):  
Miguel Martín ◽  
Antonio Jiménez-Martín ◽  
Alfonso Mateos ◽  
Josefa Z. Hernández
Keyword(s):  
Numerical Analysis ◽  
Stopping Criterion ◽  
Personalized Service ◽  
Thompson Sampling ◽  
Randomized Controlled ◽  
Testing Method ◽  
Traffic Distribution ◽  
Definition Of ◽  
Number Of Customers ◽  
Purchasing Process

A/B testing is used in digital contexts both to offer a more personalized service and to optimize the e-commerce purchasing process. A personalized service provides customers with the fastest possible access to the contents that they are most likely to use. An optimized e-commerce purchasing process reduces customer effort during online purchasing and assures that the largest possible number of customers place their order. The most widespread A/B testing method is to implement the equivalent of RCT (randomized controlled trials). Recently, however, some companies and solutions have addressed this experimentation process as a multi-armed bandit (MAB). This is known in the A/B testing market as dynamic traffic distribution. A complementary technique used to optimize the performance of A/B testing is to improve the experiment stopping criterion. In this paper, we propose an adaptation of A/B testing to account for possibilistic reward (PR) methods, together with the definition of a new stopping criterion also based on PR methods to be used for both classical A/B testing and A/B testing based on MAB algorithms. A comparative numerical analysis based on the simulation of real scenarios is used to analyze the performance of the proposed adaptations in both Bernoulli and non-Bernoulli environments. In this analysis, we show that the possibilistic reward method PR3 produced the lowest mean cumulative regret in non-Bernoulli environments, which proved to have a high confidence level and be highly stable as demonstrated by low standard deviation measures. PR3 behaves exactly the same as Thompson sampling in Bernoulli environments. The conclusion is that PR3 can be used efficiently in both environments in combination with the value remaining stopping criterion in Bernoulli environments and the PR3 bounds stopping criterion for non-Bernoulli environments.

scholarly journals Transpancreatic biliary sphincterotomy versus double guidewire in difficult biliary cannulation: a randomized controlled trial

Endoscopy ◽  
2021 ◽  
Author(s):  
Leena Kylänpää ◽  
Vilja Koskensalo ◽  
Arto Saarela ◽  
Per Ejstrud ◽  
Marianne Udd ◽  
...  
Keyword(s):  
Pancreatic Duct ◽  
Controlled Trial ◽  
Good Alternative ◽  
Endoscopic Retrograde ◽  
Biliary Cannulation ◽  
Randomized Controlled ◽  
Biliary Sphincterotomy ◽  
Difficult Biliary Cannulation ◽  
Definition Of ◽  
Randomized Method

Abstract Background Difficult biliary cannulation in endoscopic retrograde cholangiopancreatography (ERCP) increases the risk of post-ERCP pancreatitis (PEP). The purpose of this prospective, randomized, multicenter study was to compare two advanced rescue methods, transpancreatic biliary sphincterotomy (TPBS) and a double-guidewire (DGW) technique, in difficult common bile duct (CBD) cannulation. Methods Patients with native papilla and planned CBD cannulation were recruited at eight Scandinavian hospitals. An experienced endoscopist attempted CBD cannulation with wire-guided cannulation. If the procedure fulfilled the definition of difficult cannulation and a guidewire entered the pancreatic duct, randomization to either TPBS or to DGW was performed. If the randomized method failed, any method available was performed. The primary end point was the frequency of PEP and the secondary end points included successful cannulation with the randomized method. Results In total, 1190 patients were recruited and 203 (17.1 %) were randomized according to the study protocol (TPBS 104 and DGW 99). PEP developed in 14/104 patients (13.5 %) in the TPBS group and 16/99 patients (16.2 %) in the DGW group (P = 0.69). No difference existed in PEP severity between the groups. The rate of successful deep biliary cannulation was significantly higher with TPBS (84.6 % [88/104]) than with DGW (69.7 % [69/99]; P = 0.01). Conclusions In difficult biliary cannulation, there was no difference in PEP rate between TPBS and DGW techniques. TPBS is a good alternative in cases of difficult cannulation when the guidewire is in the pancreatic duct.

Randomized controlled trials

2020 ◽  
pp. 187-218
Author(s):  
Sube Banerjee ◽  
Rod S. Taylor ◽  
Jennifer Hellier
Keyword(s):  
Clinical Trial ◽  
Randomized Controlled Trials ◽  
Complex Interventions ◽  
Controlled Trials ◽  
Key Factors ◽  
Randomized Controlled ◽  
Study Population ◽  
Primary Hypothesis ◽  
Definition Of

This chapter on randomized controlled trials (RCTs) considers some of the key factors in the design, conduct, analysis, and interpretation of RCTs. The chapter provides an overview of what constitutes an RCT and why they are needed. The chapter also provides an overview of the major practical elements of the design and conduct of RCTs, including undertaking a background review of literature, the need for formulation of a clear primary hypothesis and objective, selection and definition of the study population, collecting outcomes at baseline and follow-up, and appropriate methods of statistical analysis and inference. The chapter concludes with a consideration of the need for clinical trial units, complex interventions, and alternative RCT designs.

Etude taxonomique d'entérobactéries appartenant ou apparentées à l'espèce Escherichia coli

1981 ◽  
Vol 27 (1) ◽  
pp. 98-106 ◽  
Author(s):  
F. Gavini ◽  
D. Izard ◽  
P. A. Trinel ◽  
B. Lefebvre ◽  
H. Leclerc
Keyword(s):  
Escherichia Coli ◽  
Numerical Analysis ◽  
Dna Hybridization ◽  
Dna Relatedness ◽  
E Coli ◽  
Definition Of

Phenetic (numerical analysis) and genetic (DNA–DNA hybridization) studies were carried out on strains belonging or related to the species Escherichia coli. They have shown the diversity of its phenotypes, by the presence of plasmidic characters (citrate+, urease+, H2S+, tetrathionate reductase+, raffinose+, and saccharose+). New strains related phenetically to E. coli are also individualized. They showed less than 30% DNA relatedness with E. coli. A new definition of E. coli is presented.

Peritoneal dialysis access outcomes reported in randomized controlled trials: A systematic review

2020 ◽  
pp. 089686082096689
Author(s):  
Mohamed Elbokl ◽  
Bogdan Momciu ◽  
Teruko Kishibe ◽  
Matthew J Oliver ◽  
Jeffrey Perl
Keyword(s):  
Peritoneal Dialysis ◽  
Randomized Controlled Trials ◽  
Controlled Trials ◽  
Dialysis Access ◽  
Comparative Effect ◽  
Insertion Technique ◽  
Flow Restriction ◽  
Randomized Controlled ◽  
Central Registry ◽  
Definition Of

Background: Functional peritoneal dialysis (PD) access is critical to the success of PD therapy. The aim of this review is to describe the spectrum of definitions and methods employed in the measurement of unique outcomes across PD access trials particularly focusing on the outcomes of PD access flow restriction and operative-related outcomes. Methods: Using Cochrane CENTRAL registry, MEDLINE, and EMBASE, we searched for studies restricted to randomized controlled trials (RCTs) involving interventions related to PD access without restrictions on age, language, or publication year. Studies were screened and data abstracted by two independent reviewers. Definitions, outcome measures, and time points of measurements were captured and documented separately. Unique combinations of these variables resulted in reporting the different ways of measurements. Results: Of the 1768 screened studies, 47 RCTs were included among which 817 PD access outcomes were grouped into 7 broad categories. Interventions evaluated in the RCTs were catheter type/configuration ( n = 17), insertion technique ( n = 15), multiple interventions ( n = 3), and other (6 interventions, n = 12). PD access flow restriction (a subcategory of mechanical outcomes) and operative-related outcomes were reported in 91% and 58% of the included trials, respectively. Tip migration was the most frequently reported flow restriction outcome (59% of RCTs) followed by catheter dysfunction (23% of RCTs). Of the components utilized in definition of flow restriction, description of the impaired flow was reported in 37% of RCTs, need for intervention in 42% of RCTs, and presumed etiology of flow restriction in 60% of RCTs. Conclusion: Variability exists in the definitions, reporting methods, choice of outcomes, and analysis of the PD access outcomes across RCTs. Operative-related outcomes remain underreported across RCTs. Outcomes relating to PD access flow restriction were the most common complications reported in the included RCTs but were reported heterogeneously with variability in reporting of the three key components of its definition including description and severity of the flow restriction, the need for intervention and etiology of flow restriction. In the future, defining PD access flow restriction should include all of these components to better evaluate the comparative effect of various PD access interventions.

scholarly journals Asymptotic Diffusion Analysis of Multi-Server Retrial Queue with Hyper-Exponential Service

Mathematics ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 531 ◽  
Author(s):  
Alexander Moiseev ◽  
Anatoly Nazarov ◽  
Svetlana Paul
Keyword(s):  
Numerical Analysis ◽  
Diffusion Process ◽  
Service Time ◽  
Probability Distributions ◽  
Retrial Queue ◽  
Stationary Probability ◽  
Diffusion Analysis ◽  
Number Of Customers ◽  
Multi Server

A multi-server retrial queue with a hyper-exponential service time is considered in this paper. The study is performed by the method of asymptotic diffusion analysis under the condition of long delay in orbit. On the basis of the constructed diffusion process, we obtain approximations of stationary probability distributions of the number of customers in orbit and the number of busy servers. Using simulations and numerical analysis, we estimate the accuracy and applicability area of the obtained approximations.

Conditional copula models for correlated survival endpoints: Individual patient data meta-analysis of randomized controlled trials

2021 ◽  
pp. 096228022110463
Author(s):  
Takeshi Emura ◽  
Casimir Ledoux Sofeu ◽  
Virginie Rondeau
Keyword(s):  
Randomized Controlled Trials ◽  
Individual Patient Data ◽  
Controlled Trials ◽  
Kendall’S Tau ◽  
Kendall's Tau ◽  
Randomized Controlled ◽  
Conditional Copula ◽  
Survival Endpoints ◽  
Definition Of ◽  
Meta Analyses

Correlations among survival endpoints are important for exploring surrogate endpoints of the true endpoint. With a valid surrogate endpoint tightly correlated with the true endpoint, the efficacy of a new drug/treatment can be measurable on it. However, the existing methods for measuring correlation between two endpoints impose an invalid assumption: correlation structure is constant across different treatment arms. In this article, we reconsider the definition of Kendall's concordance measure (tau) in the context of individual patient data meta-analyses of randomized controlled trials. According to our new definition of Kendall's tau, its value depends on the treatment arms. We then suggest extending the existing copula (and frailty) models so that their Kendall's tau can vary across treatment arms. Our newly proposed model, a joint frailty-conditional copula model, is the implementation of the new definition of Kendall's tau in meta-analyses. In order to facilitate our approach, we develop an original R function condCox.reg(.) and make it available in the R package joint.Cox ( https://CRAN.R-project.org/package=joint.Cox ). We apply the proposed method to a gastric cancer dataset (3288 patients in 14 randomized trials from the GASTRIC group). This data analysis concludes that Kendall's tau has different values between the surgical treatment arm and the adjuvant chemotherapy arm ( p-value<0.001), whereas disease-free survival remains a valid surrogate at individual level for overall survival in these trials.

Operationalizing the Concept of “Immobility” for Better Targeting of Thromboprophylaxis in Medical Patients: How the Literature Falls Short.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 968-968
Author(s):  
Laura Desrosiers ◽  
Susan R. Kahn ◽  
Jessica Emed
Keyword(s):  
Randomized Controlled Trials ◽  
Controlled Trials ◽  
Medical Patients ◽  
Exclusion Criteria ◽  
Vte Prophylaxis ◽  
Randomized Controlled ◽  
Thrombosis Risk ◽  
Pharmacologic Thromboprophylaxis ◽  
Definition Of ◽  
Current Guidelines

Abstract Background: Venous thromboembolism (VTE) is one of the most common, serious and preventable complications in hospitalized medical patients. Based on data from randomized trials, current guidelines recommend that pharmacologic thromboprophylaxis be administered to such patients until they are ambulatory, as immobility is a significant VTE risk factor. Hence, assessment of the ambulatory status of hospitalized patients is a key element in (1) identifying risk of VTE; and (2) decision-making regarding when to initiate and when to discontinue VTE prophylaxis. Audits continue to show low rates of thromboprophylaxis in medical patients, which could be due in part to difficulties operationalizing the terms “ambulatory” and “immobile” in the clinical setting. Clearer definitions of these terms could improve practitioners’ adherence to thromboprophylaxis guidelines. Objectives: We conducted a systematic review of trials of thromboprophylaxis in hospitalized medical patients to characterize how ambulation and immobility were defined and operationalized, and for what purpose. Methods: Pubmed and CINHAL electronic databases were searched up to August 2007 for randomized controlled trials of VTE prophylaxis in medical patients, including patients with stroke. Articles retrieved were hand-searched to identify additional trials. Definitions of “immobility”, “mobility”, “bedridden”, “bedrest”, and “confined to bed/chair” were extracted, and how the concept of mobility/immobility was used was documented. Results: Seventeen randomized controlled trials were retrieved. All studies provided definitions of the concept of “ambulation”, “mobility” or “immobility”, however definitions varied widely across studies. Twelve studies defined the concept in terms of time (definition of “ambulatory” ranged widely from <20 hours/day spent in bed, to >28 days of full “mobilizing”), 2 studies defined the concept in terms of distance (e.g. ambulatory if able to walk 10 meters), 14 studies defined the concept in terms of degree of activity (e.g. “ambulatory” if not confined to bed/chair; or if able to walk autonomously) and 11 studies used definitions that combined time or distance with degree of activity. Overall, only 11/17 studies used definitions that were clearly operationalized and could be objectively replicated. In terms of how the concept of mobility was utilized, 16 studies used the concept in inclusion or exclusion criteria, of which 11 studies provided clearly operationalized definitions; 5 studies used the concept to guide treatment (e.g. “continue treatment until patient is ambulatory”), of which 4 provided clearly operationalized definitions; and 7 studies discussed mobility in the study’s results or conclusions (e.g. “prophylaxis is appropriate in all immobilized patients”), of which 5 provided clear and operationalized definitions. Conclusions: Although all trials of VTE prophylaxis in medical patients provided definitions of the concept of mobility/immobility, there was a marked lack of consistency of such definitions across trials, many definitions could not be readily operationalized by a practitioner in clinical practice and the purpose for using mobility as a concept differed greatly among trials. In order to help clinicians better assess thrombosis risk and thereby use thromboprophylaxis more consistently in hospitalized medical patients, further research is needed to define, standardize and operationalize the concept of mobility/immobility in such patients.

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