Dealing with Inaccurate Measures of Size in Two-Stage Probability Proportional to Size Sample Designs: Applications in African Household Surveys

2020 ◽  
Author(s):  
Graham Kalton ◽  
Ismael Flores Cervantes ◽  
Carlos Arieira ◽  
Mike Kwanisai ◽  
Elizabeth Radin ◽  
...  
Keyword(s):  
Final Stage ◽  
Population Based ◽  
Equal Probability ◽  
Household Surveys ◽  
Sample Design ◽  
African Countries ◽  
Two Stage ◽  
Fixed Sample ◽  
Multi Stage ◽  
Weighting Adjustments

Abstract The units at the early stages of multi-stage area samples are generally sampled with probabilities proportional to their estimated sizes (PPES). With such a design, an overall equal probability (EP) sample design would yield a constant number of final stage units from each final stage cluster if the measures of size used in the PPES selection at each sampling stage were directly proportional to the number of final stage units. However, there are often sizable relative differences between the measures of size used in the PPES selections and the number of final stage units. Two common approaches for dealing with these differences are: (1) to retain a self-weighting sample design, allowing the sample sizes to vary across the sampled primary sampling units (PSUs) and (2) to retain the fixed sample size in each PSU and to compensate for the unequal selection probabilities by weighting adjustments in the analyses. This article examines these alternative designs in the context of two-stage sampling in which PSUs are sampled with PPES at the first stage, and an equal probability sample of final stage units is selected from each sampled PSU at the second stage. Two-stage sample designs of this type are used for household surveys in many countries. The discussion is illustrated with data from the Population-based HIV Impact Assessment surveys that were conducted using this design in several African countries.

scholarly journals Effects of Cluster Sizes on Variance Components in Two-Stage Sampling

2015 ◽  
Vol 31 (4) ◽  
pp. 763-782
Author(s):  
Richard Valliant ◽  
Jill A. Dever ◽  
Frauke Kreuter
Keyword(s):  
Sample Size ◽  
Random Effects ◽  
Variance Components ◽  
Sample Size Calculation ◽  
Household Surveys ◽  
Sample Design ◽  
Two Stage ◽  
Random Effects Models ◽  
Standard Software ◽  
The U.S

Abstract Determining sample sizes in multistage samples requires variance components for each stage of selection. The relative sizes of the variance components in a cluster sample are dramatically affected by how much the clusters vary in size, by the type of sample design, and by the form of estimator used. Measures of the homogeneity of survey variables within clusters are related to the variance components and affect the numbers of sample units that should be selected at each stage to achieve the desired precision levels. Measures of homogeneity can be estimated using standard software for random-effects models but the model-based intracluster correlations may need to be transformed to be appropriate for use with the sample design. We illustrate these points and implications for sample size calculation for two-stage sample designs using a realistic population derived from household surveys and the decennial census in the U.S.

Leading-Effect, Risk-Taking and Sabotage in Two-Stage Tournaments: Evidence from a Natural Experiment

2019 ◽  
Vol 237 (1) ◽  
pp. 1-28
Author(s):  
Frank Mueller-Langer ◽  
Patrick Andreoli-Versbach
Keyword(s):  
Risk Taking ◽  
Final Stage ◽  
Natural Experiment ◽  
Initial Conditions ◽  
Order Effects ◽  
Information Feedback ◽  
Two Stage ◽  
Multi Stage ◽  
Increase Risk

Abstract Existing theory suggests that three “order effects” may emerge in multi-stage tournaments with information feedback. First, participants adjust effort across stages, which could advantage the leading participant who faces a larger “effective prize” after an initial victory (leading-effect). Second, leading participants might engage in sabotage activities to protect their lead thereby decreasing the rivals’ output. Finally, participants lagging behind may increase risk at the final stage as they have “nothing to lose” (risk-taking). The expected order effects based on existing theory cannot be supported empirically in a natural experiment setting, where professional teams compete in a two-stage tournament with asymmetric initial conditions and clear incentives.

scholarly journals Generalized optimizations of two-stage forging of micro/meso copper fastener

2018 ◽  
Vol 185 ◽  
pp. 00002
Author(s):  
Shih-Hsien Lin ◽  
Un-Chin Chai ◽  
Gow-Yi Tzou ◽  
Dyi-Cheng Chen
Keyword(s):  
Simulation Analysis ◽  
Effective Strain ◽  
Cold Forging ◽  
Two Stage ◽  
Forming Simulation ◽  
Multi Stage ◽  
Element Simulation ◽  
Die Stress ◽  
Stress Optimization ◽  
Forging Force

Three are generalized simulation optimizations considering the forging force, the die stress, and the dual-goals in two-stage forging of micro/meso copper fastener. Constant shear friction between the dies and workpiece is assumed to perform multi-stage cold forging forming simulation analysis, and the Taguchi method with the finite element simulation has been used for mold-and-dies parameters design simulation optimizations considering the forging force, die stress, and dual-goals. The die stress optimization is used to explore the effects on effective stress, effective strain, velocity field, die stress, forging force, and shape of product. The influence rank to forging process of micro/meso copper fastener for three optimizations can be determined, and the optimal parameters assembly consider die stress can be obtained in this study. It is noted that the punch design innovation can reduce the forging force and die stress.

scholarly journals Use, awareness and willingness to self-test for HIV: An analysis of cross-sectional population-based surveys in Malawi and Zimbabwe

2020 ◽  
Author(s):  
Cheryl Case Johnson ◽  
Melissa Neuman ◽  
Peter MacPherson ◽  
Augustine Choko ◽  
Caitlin Quinn ◽  
...  
Keyword(s):  
Sexual Risk ◽  
Large Scale ◽  
Scale Up ◽  
Population Level ◽  
Sociodemographic Factors ◽  
Population Based ◽  
African Countries ◽  
Cross Sectional ◽  
Self Test ◽  
Result Analysis

Abstract Background Many southern African countries are nearing the global goal to diagnose 90% of people with HIV by 2020. In 2016, 84% and 86% of people with HIV knew their status in Malawi and Zimbabwe respectively. Despite this progress, gaps remain, particularly among men (≥25 years). We investigated awareness, use and willingness to HIV self-test (HIVST) prior to large scale implementation and explored sociodemographic associations. Methods We pooled responses from two of the first cross-sectional Demographic Health Surveys to include HIVST questions: Malawi and Zimbabwe in 2015-16. Sociodemographic factors and sexual risk behaviours associated with previously testing for HIV, and awareness, past use and future willingness to self-test were investigated using univariable and multivariable logistic regression, adjusting for the sample design and limiting analysis to participants with completed questionnaire and a valid HIV result. Analysis of willingness to self-test was restricted to Zimbabwean men, as Malawians and women were not asked this question. Results Of 31 385 individuals, the proportion never-tested was higher for men (31.2%) than women (16.5%), p<0.001. For men, having ever tested increased with age. Past use and awareness of HIVST was very low, 1.2% and 12.6% respectively. Awareness was lower among women than men (9.1% vs 15.3%, adjusted odds ratio (aOR)=1.55; 95% confidence interval [CI]: 1.37-1.75), and at younger ages, and lower education and literacy levels. Willingness to self-test among Zimbabwean men was high (84.5%), with having previously tested for HIV, high sexual risk, and being ≥25 years associated with greater willingness. Wealthier men had greater awareness of HIVST than poorer men (p<0.001). Men at higher HIV-related sexual risk, compared to men at lower HIV-related sexual risk, had the greatest willingness to self-test (aOR=3.74; 95%CI: 1.39-10.03, p<0.009).Conclusions In 2015-16 many Malawian and Zimbabwean men had never tested for HIV. Despite low awareness and minimal HIVST experience at that time, willingness to self-test was high among Zimbabwean men, especially in older men with moderate to high HIV-related sexual risk. These data provide a valuable baseline against which to investigate population-level uptake of HIVST as programmes scale-up. Programmes introducing, or planning to introduce HIVST, should consider including questions in population-based surveys.

scholarly journals Two-Stage Single-Arm Trials Are Rarely Analyzed Effectively or Reported Adequately

2021 ◽  
pp. 1813-1820
Author(s):  
Michael J. Grayling ◽  
Adrian P. Mander
Keyword(s):  
Final Stage ◽  
Interim Analysis ◽  
Primary Outcome ◽  
Point Estimate ◽  
Two Stage ◽  
Stage Design ◽  
Patient Subgroup ◽  
Future Studies ◽  
Point Estimates ◽  
Outcome Trial

PURPOSE Two-stage single-arm designs have historically been the most common design used in phase II oncology. They remain a mainstay today, particularly for trials in rare subgroups. Consequently, it is imperative such studies be designed, analyzed, and reported effectively. We comprehensively review such trials to examine whether this is the case. METHODS Oncology trials that used Simon's two-stage design over a 5-year period were identified and reviewed. They were evaluated for whether they reported sufficient design (eg, required sample size) and analysis (eg, CI) details. Articles that did not adjust their inference for the incorporation of an interim analysis were also reanalyzed. RESULTS Four-hundred twenty-five articles were included. Of these, just 47.5% provided the five components that ensure design reproducibility. Only 1.2% and 2.1% reported an adjusted point estimate or CI, respectively. Just 55.3% provided the final stage rejection bound, indicating many trials did not test a hypothesis for their primary outcome. Trial reanalyses suggested reported point estimates underestimated treatment effects and reported CIs were too narrow. CONCLUSION Key design details of two-stage single-arm trials are often unreported. Their inference is rarely performed such as to remove bias introduced by the interim analysis. These findings are particular alarming when considered against the growing trend in which nonrandomized trials make up a large proportion of all evidence on a treatment's effectiveness in a rare biomarker-defined patient subgroup. Future studies must improve the way they are analyzed and reported.

scholarly journals Enteric Fever in Mediterranean North Africa

2009 ◽  
Vol 3 (10) ◽  
pp. 753-761 ◽  
Author(s):  
Khalifa Sifaw Ghenghesh ◽  
Ezzedin Franka ◽  
Khaled Tawil ◽  
Momtaz Wasfy ◽  
Salwa F. Ahmed ◽  
...  
Keyword(s):  
North Africa ◽  
Salmonella Enterica ◽  
Enteric Fever ◽  
Salmonella Typhi ◽  
Multidrug Resistant ◽  
Population Based ◽  
North African ◽  
African Region ◽  
African Countries ◽  
The Mediterranean

Typhoid fever is endemic in the Mediterranean North African countries (Morocco, Algeria, Tunisia, Libya, and Egypt) with an estimated incidence of 10-100 cases per 100,000 persons. Outbreaks caused by Salmonella enterica serovar Typhi are common and mainly due to the consumption of untreated or sewage-contaminated water. Salmonella enterica Paratyphi B is more commonly involved in nosocomial cases of enteric fever in North Africa than expected and leads to high mortality rates among infants with congenital anomalies. Prevalence among travellers returning from this region is low, with an estimate of less than one per 100,000. Although multidrug resistant strains of Salmonella Typhi and Paratyphi are prevalent in this region, the re-emergence of chloramphenicol- and ampicillin-susceptible strains has been observed. In order to better understand the epidemiology of enteric fever in the Mediterranean North African region, population-based studies are needed. These will assist the health authorities in the region in preventing and controlling this important disease.

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