scholarly journals Better together? Regression analysis of complex survey data after ex-post harmonization

2020 ◽  
Author(s):  
Anna-Carolina Haensch ◽  
Bernd Weiß
Keyword(s):  
Regression Analysis ◽  
Survey Data ◽  
Random Effects ◽  
Two Stage ◽  
Complex Sampling ◽  
One Stage ◽  
Ex Post ◽  
Study Heterogeneity ◽  
Research Questions ◽  
Stage Analysis

An increasing number of researchers pool, harmonize, and analyze survey data from different survey providers for their research questions. They aim to study heterogeneity between groups over a long period or examine smaller subgroups; research questions that can be impossible to answer with a single survey. This combination or pooling of data is known as individual person data (IPD) meta-analysis in medicine and psychology; in sociology, it is understood as part of ex-post survey harmonization (Granda et al 2010).However, in medicine or psychology, most original studies focus on treatment or intervention effect and apply experimental research designs to come to causal conclusions. In contrast, many sociological or economic studies are nonexperimental. In comparison to experimental data, survey-based data is subject to complex sampling and nonresponse. Ignoring the complex sampling design can lead to biased population inferences not only in population means and shares but also in regression coefficients, widely used in the social sciences (DuMouchel and Duncan 1983 and Solon et al. 2013). To account for complex sampling schemes or non-ignorable unit nonresponse, survey-based data often comes with survey weights. But how to use survey weights after pooling different surveys?We will build upon the work done by DuMouchel and Duncan (1983) and Solon et al. (2013) for survey-weighted regression analysis with a single data set. Through Monte Carlo (MC) simulations, we will show that endogenous sampling and heterogeneity of effects models require survey weighting to receive approximately unbiased estimates after ex-post survey harmonization. Second, we focus on a list of methodological questions: Do survey-weighted one-stage and two-stage (meta-)analytical approaches perform differently? Is it possible to include random effects, especially if we have to assume study heterogeneity? Another challenging methodological question is the inclusion of random effects in a one-stage analysis.Our simulations show that two-stage analysis will be biased if the weights' variation is high, whereas one-stage analysis remains unbiased. We also show that the inclusion of random effects in a one-stage analysis is challenging but doable, i.e., weights must be transformed in most cases. Apart from the MC simulations, we also show the difference between two-stage and one-stage approaches with real-world data from same-sex couples in Germany.

Nonlinear Random Wave Time Domain Analysis of Jack-Up Rigs Including Foundation

2017 ◽  
Author(s):  
Partha Chakrabarti ◽  
Deepak Sankar Somasundaram ◽  
Abhijeet Chawan
Keyword(s):  
Time Domain ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Analysis Procedure ◽  
Random Wave ◽  
Two Stage ◽  
Deterministic Analysis ◽  
One Stage ◽  
Stage Analysis ◽  
Jack Up

A jack-up rig has to be designed for extreme storm conditions in its elevated mode during operations. Guidelines of ISO 19905-1 [1] and SNAME TR-5-5A [2] for site specific assessment of jack-up rigs explain in detail such analysis and assessment requirements. It is well known that for higher water depths and extreme environment, structural dynamics and spudcan-soil interaction plays a very significant role. The extreme storm response can be determined either by a two-stage deterministic storm analysis procedure using a quasi-static analysis that includes an inertial load set or by a more detailed fully integrated (random wave) dynamic analysis procedure that uses a stochastic analysis. More commonly, however, jack-up rigs are assessed using a two-stage deterministic wave model along with steady wind loads, since this is much simpler. In two-stage deterministic analysis, the first step is the determination of the inertial load set and structural analysis for all the environmental and gravity loads. To include the effects of the spudcan and soil foundation, an initial rotational stiffness or fixity is assumed that depends on the soil type and the preload. Assessment of the foundation is performed thereafter using the yield interaction approach. This is normally an iterative approach to arrive at the right fixity that satisfies the assessment. The two-stage approach, although simpler could be conservative leading to adverse conclusions for the suitability of a jack-up at a site. As indicated, the other approach is the one-stage approach involving random time domain analysis which is normally not used and reported in the literature probably due to its complexity and difficulty. The present paper describes random wave time domain analysis of a specific jack-up using a 3D model in 400 ft water depth using USFOS software [3]. This software has the spudcan-soil interaction integrated, to simulate the foundation behavior. In this one-stage analysis, the assessment for the foundation is performed through an iterative approach inside the software using yield and bounding surfaces. Extreme values of some of key responses are compared with traditional deterministic analysis. Benefits and limitations of random wave time domain analysis are explained and quantified. These benefits are sometimes so significant that one-stage analysis may lead to favorable conclusions where the conservative two-stage analysis approach had failed to show the adequacy of the rig. These observations and the overall methodology of analysis used here could be beneficial to any rig’s applicability at a specific site.

scholarly journals EFFECT OF GENDER AND EDUCATIONAL QUALIFICATION ON ADMINISTRATIVE EFFECTIVENESS OF LIBRARIANS IN FEDERAL UNIVERSITIES IN SOUTH-SOUTH NIGERIA

2021 ◽  
Vol 2 (2) ◽  
pp. 14-28
Author(s):  
C. O. Offem ◽  
M. O. Otun
Keyword(s):  
Regression Analysis ◽  
Multiple Regression Analysis ◽  
Sampling Technique ◽  
Questionnaire Data ◽  
University Libraries ◽  
Educational Qualification ◽  
Ex Post ◽  
Administrative Effectiveness ◽  
Ex Post Facto ◽  
Research Questions

The study was carried out to determine the effect of gender and educational qualification on the administrative effectiveness of librarians in federal universities in South-South Nigeria. The study adopted the non-probability sampling technique together with the ex-post facto research design which implemented the purposive and accidental sampling technique in choosing the population. A total of two hundred and thirty-one (231) respondents were chosen from six federal university libraries which comprised one hundred and seven professional (107) librarians and one hundred and twenty-four (124) Para-professionals. Data were elicited through a questionnaire. Data were analyzed using both descriptive and inferential statistics (independent t-test, one-way analysis of variance and multiple regression analysis. The research questions were answered and the hypotheses were tested at 0.05 levels of significance. Results show that there is a positive correlation between educational qualification and administrative effectiveness of librarians in the South-South universities of Nigeria. Secondly, a significant result was obtained for gender as a predictor of administrative effectiveness of librarians. The study, therefore, recommends that employers of librarians should allow them to improve themselves via acquiring postgraduate qualifications such as a master’s degree and PhD as this will go a long way to add value to them and improved their skills.

Analysis of Data from a Controlled Repeated Measurements Design with Baseline-Dependent Dropouts

Methodology ◽  
2007 ◽  
Vol 3 (2) ◽  
pp. 58-66 ◽  
Author(s):  
John E. Overall ◽  
Scott Tonidandel
Keyword(s):  
Monte Carlo ◽  
Random Effects ◽  
Repeated Measurements ◽  
Random Effects Model ◽  
Two Stage ◽  
Linear Interaction ◽  
Rates Of Change ◽  
Type 1 Error ◽  
Stage Analysis

Abstract. Differences in mean rates of change are of primary interest in many controlled treatment evaluation studies. Generalized linear mixed model (GLMM) procedures are widely conceived to be the preferred method of analysis for repeated measurement designs when there are missing data due to dropouts, but systematic dependence of the dropout probabilities on antecedent or concurrent factors poses a problem for testing the significance of differences in mean rates of change across time in such designs. Controlling for the dependence of dropout probabilities on baseline values poses a special problem because a theoretically correct GLMM random-effects model does not permit including the same baseline score as both covariate and dependent variable. Monte Carlo methods are used herein to evaluate the actual Type 1 error rates and power resulting from two commonly-illustrated GLMM random-effects model formulations for testing the GROUPS × TIMES linear interaction effect in group-randomized repeated measurements designs. The two GLMM model formulations differ by either including or not including baseline scores as a covariate in the attempt to control for imbalance caused by the baseline-dependent dropouts. Results from those analyses are compared with results from a simpler two-stage analysis in which dropout-weighted slope coefficients fitted separately to the available repeated measurements for each subject serve as the dependent variable for an ordinary ANCOVA test for difference in mean rates of change. The Monte Carlo results confirm modestly superior Type 1 error protection but quite superior power for the simpler two-stage analysis of dropout-weighted slope coefficients as compared with those for either of the more mathematically complex GLMM analyses.

Abstract P343: Comparison of Two-stage and One-stage Meta-analyses: An Example of eGFR-Cardiovascular Mortality Association (for CKD-PC collaborators)

Circulation ◽  
2012 ◽  
Vol 125 (suppl_10) ◽  
Author(s):  
Yingying Sang ◽  
Kunihiro Matsushita ◽  
Bakhtawar K Mahmoodi ◽  
Brad C Astor ◽  
Josef Coresh ◽  
...  
Keyword(s):  
Random Effects ◽  
Cardiovascular Mortality ◽  
Cox Model ◽  
Meta Analysis ◽  
Fixed Effect ◽  
Two Stage ◽  
Statistical Estimates ◽  
One Stage ◽  
Individual Participant ◽  
Meta Analyses

Purpose: Individual participant data (IPD) meta-analysis provides precise statistical estimates. Two approaches to meta-analyze IPD are currently used. The 1-stage approach fits a regression model to a pooled dataset including all studies. The 2-stage approach fits models in individual studies and meta-analyzes the estimates. However, their comparability has not been well described. We compare these methods for eGFR-cardiovascular mortality association in the CKD Prognosis Consortium (CKD-PC). Methods: For the 1-stage method, we fitted a Cox stratified model, allowing each study to have a unique baseline hazard but assuming a common hazard ratio (HR) for eGFR across studies. For the 2-stage method, we first fitted a Cox model in each study, and then meta-analyzed HRs using a fixed-effect (assuming one true HR for eGFR across studies) and a random-effects (allowing some variance of true HR) model. eGFR was fitted as linear splines in all models. Results: In a sample of 18 of 46 cohorts joining CKD-PC (191,276 participants and 8,732 cardiovascular deaths [CHD, stroke, or heart failure]), these methods gave nearly identical estimates except for the width of the confidence intervals ( Figure ). The 95% CIs were wider as methods made fewer assumptions - narrowest for 1-stage method, slightly wider for the fixed-effect 2-stage and wider for the random-effects 2-stage method. Conclusion: The two-stage and one-stage meta-analyses provided nearly identical estimates for the eGFR-cardiovascular mortality relationship. The random-effects 2-stage method will provide conservative estimates with wider 95% CIs but this is necessary in the presence of heterogeneity.

scholarly journals Drug-coated balloons for dysfunctional hemodialysis venous access: A patient-level meta-analysis of randomized controlled trials

2020 ◽  
Author(s):  
Fong Khi Yung ◽  
Joseph J Zhao ◽  
Eelin Tan ◽  
Nicholas Syn ◽  
Rehena Sultana ◽  
...  
Keyword(s):  
Random Effects ◽  
Meta Analysis ◽  
Venous Access ◽  
Primary Patency ◽  
Two Stage ◽  
Patient Level ◽  
Randomized Controlled ◽  
One Stage ◽  
Shared Frailty ◽  
Meta Analyses

ABSTRACTPurposeTo perform an individual patient data-level meta-analysis of randomized controlled trials comparing drug-coated balloon angioplasty (DCB) against conventional percutaneous transluminal angioplasty (PTA) in the treatment of dysfunctional hemodialysis venous access.MethodsA search was conducted from inception till 13th November 2020. Kaplan-Meier curves comparing DCB to PTA by target lesion primary patency (TLPP) and access circuit primary patency (ACPP) were graphically reconstructed to retrieve patient-level data. One-stage meta-analyses with Cox-models with random-effects gramma-frailties were conducted to determine hazard ratios (HRs). Dynamic restricted mean survival times (RMST) were conducted in view of violation of the proportional hazards assumption. Conventional two-stage meta-analyses and network meta-analyses under random-effects Frequentist models were conducted to determine overall and comparative outcomes of paclitaxel concentrations utilised. Where outliers were consistently detected through outlier and influence analyses, sensitivity analyses excluding those studies were conducted.ResultsAmong 10 RCTs (1,207 patients), HRs across all models favoured DCB (one-stage shared-frailty HR=0.62, 95%-CI: 0.53–0.73, P<0.001; two-stage random-effects HR=0.60, 95%-CI: 0.42–0.86, P=0.018, I2=65%) for TLPP. Evidence of time-varying effects (P=0.005) was found. TLPP RMST was +3.47 months (25.0%) longer in DCB-treated patients compared to PTA (P=0.001) at 3-years. TLPP at 6-months, 1-year and 2-years was 75.3% vs 58.0%, 51.1% vs 37.1% and 31.3% vs 26.0% for DCB and PTA respectively. P-Scores within the Frequentist network meta-analysis suggest that higher concentrations of paclitaxel were associated with better TLPP and ACPP. Among 6 RCTs (854 patients), the one-stage model favoured DCB (shared-frailty HR=0.72, 95%-CI: 0.60–0.87, P<0.001) for ACPP. Conversely, the two-stage random-effects model demonstrated no significant difference (HR=0.76, 95%-CI: 0.35–1.67, P=0.414, I2=81%). Sensitivity analysis excluding outliers significantly favoured DCB (HR=0.61, 95%-CI: 0.41–0.91, P=0.027, I2=62%).ConclusionOverall evidence suggests that DCB is favoured over PTA in TLPP and ACPP. The increased efficacy of higher concentrations of paclitaxel may warrant further investigation.

Molecular genetic background of haemophilia A patients with discrepancy between one-stage and two-stage factor VIII assays

2010 ◽  
Vol 30 (S 01) ◽  
pp. S153-S155
Author(s):  
D. Delev ◽  
S. Pahl ◽  
J. Driesen ◽  
H. Brondke ◽  
J. Oldenburg ◽  
...  
Keyword(s):  
Factor Viii ◽  
Genetic Background ◽  
Molecular Genetic ◽  
Haemophilia A ◽  
Two Stage ◽  
One Stage

Plasma Factor V Activation Is Prevented by Activated Protein C in the Presence of Phospholipid Vesicles, Not Platelets

1993 ◽  
Vol 69 (02) ◽  
pp. 124-129 ◽  
Author(s):  
Susan Solymoss ◽  
Kim Thi Phu Nguyen
Keyword(s):  
Western Blotting ◽  
Protein C ◽  
Thrombin Generation ◽  
Blood Platelets ◽  
Activated Protein C ◽  
Phospholipid Vesicles ◽  
Factor V ◽  
Two Stage ◽  
One Stage ◽  
Plasma Factor

SummaryActivated protein C (APC) is a vitamin K dependent anticoagulant which catalyzes the inactivation of factor Va and VIIIa, in a reaction modulated by phospholipid membrane surface, or blood platelets. APC prevents thrombin generation at a much lower concentration when added to recalcified plasma and phospholipid vesicles, than recalcified plasma and platelets. This observation was attributed to a platelet associated APC inhibitor. We have performed serial thrombin, factor V one stage and two stage assays and Western blotting of dilute recalcified plasma containing either phospholipid vesicles or platelets and APC. More thrombin was formed at a given APC concentration with platelets than phospholipid. One stage factor V values increased to higher levels with platelets and APC than phospholipid and APC. Two stage factor V values decreased substantially with platelets and 5 nM APC but remained unchanged with phospholipid and 5 nM APC. Western blotting of plasma factor V confirmed factor V activation in the presence of platelets and APC, but lack of factor V activation with phospholipid and APC. Inclusion of platelets or platelet membrane with phospholipid enhanced rather than inhibited APC catalyzed plasma factor V inactivation. Platelet activation further enhanced factor V activation and inactivation at any given APC concentration.Plasma thrombin generation in the presence of platelets and APC is related to ongoing factor V activation. No inhibition of APC inactivation of FVa occurs in the presence of platelets.

Two-Stage Procedure for the Quantitative Determination of Autoprothrombin III Concentration and Some Applications

1967 ◽  
Vol 18 (01/02) ◽  
pp. 198-210 ◽  
Author(s):  
Ronald S Reno ◽  
Walter H Seegers
Keyword(s):  
Prothrombin Time ◽  
Factor Vii ◽  
Two Stage ◽  
Pronounced Increase ◽  
One Stage ◽  
Assay Procedure ◽  
Bovine Plasma ◽  
The One ◽  
Autoprothrombin C

SummaryA two-stage assay procedure was developed for the determination of the autoprothrombin C titre which can be developed from prothrombin or autoprothrombin III containing solutions. The proenzyme is activated by Russell’s viper venom and the autoprothrombin C activity that appears is measured by its ability to shorten the partial thromboplastin time of bovine plasma.Using the assay, the autoprothrombin C titre was determined in the plasma of several species, as well as the percentage of it remaining in the serum from blood clotted in glass test tubes. Much autoprothrombin III remains in human serum. With sufficient thromboplastin it was completely utilized. Plasma from selected patients with coagulation disorders was assayed and only Stuart plasma was abnormal. In so-called factor VII, IX, and P.T.A. deficiency the autoprothrombin C titre and thrombin titre that could be developed was normal. In one case (prethrombin irregularity) practically no thrombin titre developed but the amount of autoprothrombin C which generated was in the normal range.Dogs were treated with Dicumarol and the autoprothrombin C titre that could be developed from their plasmas decreased until only traces could be detected. This coincided with a lowering of the thrombin titre that could be developed and a prolongation of the one-stage prothrombin time. While the Dicumarol was acting, the dogs were given an infusion of purified bovine prothrombin and the levels of autoprothrombin C, thrombin and one-stage prothrombin time were followed for several hours. The tests became normal immediately after the infusion and then went back to preinfusion levels over a period of 24 hrs.In other dogs the effect of Dicumarol was reversed by giving vitamin K1 intravenously. The effect of the vitamin was noticed as early as 20 min after administration.In response to vitamin K the most pronounced increase was with that portion of the prothrombin molecule which yields thrombin. The proportion of that protein with respect to the precursor of autoprothrombin C increased during the first hour and then started to go down and after 3 hrs was equal to the proportion normally found in plasma.

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