A Power Comparison of Various Tests of Univariate Normality on Ex-Gaussian Distributions

Methodology ◽  
2013 ◽  
Vol 9 (4) ◽  
pp. 137-149 ◽  
Author(s):  
Fernando Marmolejo-Ramos ◽  
Jorge González-Burgos
Keyword(s):  
Confidence Intervals ◽  
Gaussian Distribution ◽  
Power Analysis ◽  
Meta Analysis ◽  
Reaction Times ◽  
Critical Values ◽  
Future Research ◽  
Power Comparison ◽  
Gaussian Distributions ◽  
Power Analyses

A power analysis of seven normality tests against the Ex-Gaussian distribution (EGd) is presented. The EGd is selected on the basis that it is a particularly well-suited distribution to accommodate positively skewed distributions such as those observed in reaction times data. A pre-assessment of the power of the selected tests across various types of distributions was done via a meta-analysis and a comparison with other power analyses reported in the literature was also performed. General recommendations are given as to which tests should be used to test normality in data suspected to resemble an EG distribution. Additionally, some topics for future research regarding the use of confidence intervals and the computation of accurate critical values are outlined.

How Many Studies Do You Need?

2010 ◽  
Vol 35 (2) ◽  
pp. 215-247 ◽  
Author(s):  
Jeffrey C. Valentine ◽  
Therese D. Pigott ◽  
Hannah R. Rothstein
Keyword(s):  
Confidence Intervals ◽  
Random Effects ◽  
Power Analysis ◽  
Variance Component ◽  
Statistical Power ◽  
Meta Analysis ◽  
Inclusion Criteria ◽  
Fixed And Random Effects ◽  
Quantitative Synthesis ◽  
Power Analyses

In this article, the authors outline methods for using fixed and random effects power analysis in the context of meta-analysis. Like statistical power analysis for primary studies, power analysis for meta-analysis can be done either prospectively or retrospectively and requires assumptions about parameters that are unknown. The authors provide some suggestions for thinking about these parameters, in particular for the random effects variance component. The authors also show how the typically uninformative retrospective power analysis can be made more informative. The authors then discuss the value of confidence intervals, show how they could be used in addition to or instead of retrospective power analysis, and also demonstrate that confidence intervals can convey information more effectively in some situations than power analyses alone. Finally, the authors take up the question “How many studies do you need to do a meta-analysis?” and show that, given the need for a conclusion, the answer is “two studies,” because all other synthesis techniques are less transparent and/or are less likely to be valid. For systematic reviewers who choose not to conduct a quantitative synthesis, the authors provide suggestions for both highlighting the current limitations in the research base and for displaying the characteristics and results of studies that were found to meet inclusion criteria.

scholarly journals Investigating placental pathologies in pregnant women with SARS-CoV-2: Systematic Review and Meta-analysis Protocol

2020 ◽  
Author(s):  
Irina Oltean ◽  
Dina El Demellawy ◽  
Margaret Sampson
Keyword(s):  
Systematic Review ◽  
Pregnant Women ◽  
Confidence Intervals ◽  
Vertical Transmission ◽  
Meta Analysis ◽  
Case Series ◽  
Medical Attention ◽  
Future Research ◽  
Third Trimester ◽  
Statistical Heterogeneity

An investigation into placental pathology in pregnant women with SARS-CoV-2 has not yet been examined extensively; however, this knowledge would be beneficial in understanding the potential for vertical transmission of SARS-CoV-2 during pregnancy, via the placenta. Currently, results are conflicting, with some evidence suggesting rare placental infection. Conversely, compared to controls, one study determined that third trimester placentas were significantly more likely to show one feature of maternal vascular malperfusion (MVM), and intervillous thrombi, fetal vascular malperfusion or fetal vascular thrombosis, and increased perivillous fibrin deposition and intervillositis. In contrast, another study reported no significant differences in individual or group gross or microscopic pathological features. As well, no ACE2 expression has yet been detected in villous stroma, Hofbauer cells, or endothelial cells, and TMPRSS2 expression is only weakly present in villous endothelium. In light of the inconclusive evidence, the burden of placental pathologies potentially related to SARS-CoV-2 in pregnant women and their neonates or infants, remains at the forefront of medical attention, particularly among pathologists, and obstetricians worldwide. This protocol describes the steps of our systematic review, which aims to investigate differences in placental pathologies in pregnant women with SARS-CoV-2 versus pregnant women without the virus. Our study will identify case series, case-control and cohort studies of asymptomatic and symptomatic pregnant women, who test positive for SARS-CoV-2 during any stage of their pregnancy, as validated by laboratory confirmed positive antibody testing or using real-time reverse-transcriptase-polymerase chain reaction (rRT-PCR). Studies examining pregnant women who test positive during the first, second or third trimester, are eligible. Only articles written in English or French will be included. Literature reviews, systematic reviews, editorials, letters to the editor, conference abstracts, and commentaries will be excluded. The following databases will be searched: MEDLINE including Epub Ahead of Print, In-Process & Other Non-Indexed Citations (1946- November 17, 2020) and Embase (1980- November 17, 2020). Two specialized COVID-19 resources will also be searched November 18, 2020; Cochrane Covid-19 study register which indexes according to study design, and the WHO Covid-19 Collection which includes material from numerous sources including preprint servers. Primary outcomes of interest are: retroplacental hematoma, diffuse parenchymal consolidation, maternal vascular malperfusion, fetal vascular malperfusion, and other diseases of the placenta as detailed in this protocol. Observational studies will be assessed using the Ottawa-Newcastle scale. Data will be aggregated or synthesized at the level of individual participants. Tables will be used to summarize the general characteristics of the studies included. Depending on the data and the level of variation between studies, a meta-analysis will be used to synthesize data. Count and dichotomous data will be expressed as odds ratios with 95% confidence intervals, while continuous data will be expressed as a mean or standardized mean difference with 95% confidence intervals. Statistical heterogeneity of the included studies will be assessed using the I-squared test with 95% confidence intervals, and publication bias will be determined using a funnel plot and Egger’s test when possible (>10 included studies). This review will ultimately aid in informing pathologists, obstetricians, and gynecologists when managing and treating pregnant women with SARS-CoV-2. If no evidence of vertical transmission or changes to placenta can be elucidated, then this work can inform future research investigating alternate routes of SARS-CoV-2 transmission.

Chasing the Anchor: A Systematic Review and Meta-analysis of Perceptual Anchoring Deficits in Developmental Dyslexia

2020 ◽  
Author(s):  
Kurt D Shulver ◽  
Nicholas A Badcock
Keyword(s):  
Systematic Review ◽  
Reading Ability ◽  
English Language ◽  
Prediction Interval ◽  
Meta Analysis ◽  
Visual Assessment ◽  
Individual Performance ◽  
Future Research ◽  
Significant Heterogeneity ◽  
Eligibility Criteria

We report the results of a systematic review and meta-analysis investigating the relationship between perceptual anchoring and dyslexia. Our goal was to assess the direction and degree of effect between perceptual anchoring and reading ability in typical and atypical (dyslexic) readers. We performed a literature search of experiments explicitly assessing perceptual anchoring and reading ability using PsycInfo (Ovid, 1860 to 2020), MEDLINE (Ovid, 1860 to 2019), EMBASE (Ovid, 1883 to 2019), and PubMed for all available years up to June (2020). Our eligibility criteria consisted of English-language articles and, at minimum, one experimental group identified as dyslexic - either by reading assessment at the time, or by previous diagnosis. We assessed for risk of bias using an adapted version of the Newcastle-Ottawa scale. Six studies were included in this review, but only five (n = 280 participants) were included in the meta-analysis (we were unable to access the necessary data for one study).The overall effect was negative, large and statistically significant; g = -0.87, 95% CI [-1.47, 0.27]: a negative effect size indicating less perceptual anchoring in dyslexic versus non-dyslexic groups. Visual assessment of funnel plot and Egger’s test suggest minimal bias but with significant heterogeneity; Q (4) = 9.70, PI (prediction interval) [-2.32, -0.58]. The primary limitation of the current review is the small number of included studies. We discuss methodological limitations, such as limited power, and how future research may redress these concerns. The variability of effect sizes appears consistent with the inherent variability within subtypes of dyslexia. This level of dispersion seems indicative of the how we define cut-off thresholds between typical reading and dyslexia populations, but also the methodological tools we use to investigate individual performance.

Autobiographical Memory Impairments as a Transdiagnostic Feature of Mental Illness: A meta-analysis of autobiographical memory specificity and overgenerality amongst people with psychiatric diagnoses

2020 ◽  
Author(s):  
Tom Joseph Barry ◽  
David John Hallford ◽  
Keisuke Takano
Keyword(s):  
Autobiographical Memory ◽  
Memory Retrieval ◽  
Keyword Search ◽  
Meta Analysis ◽  
Future Research ◽  
Psychiatric Diagnoses ◽  
Schizophrenia Spectrum Disorders ◽  
Memory Impairments ◽  
Memory Specificity ◽  
Causal Mechanisms

Decades of research has examined the difficulty that people with psychiatric diagnoses, such as Major Depressive Disorder, Schizophrenia Spectrum Disorders, and Posttraumatic Stress Disorder, have in recalling specific autobiographical memories from events that lasted less than a day. Instead, they seem to retrieve general events that have occurred many times or which occurred over longer periods of time, termed overgeneral memory. We present the first transdiagnostic meta-analysis of memory specificity/overgenerality, and the first meta-regression of proposed causal mechanisms. A keyword search of Embase, PsycARTICLES and PsycINFO databases yielded 74 studies that compared people with and without psychiatric diagnoses on the retrieval of specific (k = 85) or general memories (k = 56). Multi-level meta-analysis confirmed that people with psychiatric diagnoses typically recall fewer specific (g = -0.864, 95% CI[-1.030, -0.698]) and more general (g = .712, 95% CI[0.524, 0.900]) memories than diagnoses-free people. The size of these effects did not differ between diagnostic groups. There were no consistent moderators; effect sizes were not explained by methodological factors such as cue valence, or demographic variables such as participants’ age. There was also no support for the contribution of underlying processes that are thought to be involved in specific/general memory retrieval (e.g., rumination). Our findings confirm that deficits in autobiographical memory retrieval are a transdiagnostic factor associated with a broad range of psychiatric problems, but future research should explore novel causal mechanisms such as encoding deficits and the social processes involved in memory sharing and rehearsal.

Challenges and Opportunities for Neuroimaging in Young Patients with Traumatic Brain Injury: a Coordinated Effort towards Advancing Discovery from the ENIGMA Pediatric Moderate/Severe TBI Group

2019 ◽  
Author(s):  
Emily L. Dennis ◽  
Karen Caeyenberghs ◽  
Robert F. Asarnow ◽  
Talin Babikian ◽  
Brenda Bartnik-Olson ◽  
...  
Keyword(s):  
Traumatic Brain Injury ◽  
Brain Injury ◽  
Meta Analysis ◽  
Young Patients ◽  
Future Research ◽  
Childhood And Adolescence ◽  
Developmental Issues ◽  
Challenges And Opportunities ◽  
Severe Tbi ◽  
Advance Research

Traumatic brain injury (TBI) is a major cause of death and disability in children in both developed and developing nations. Children and adolescents suffer from TBI at a higher rate than the general population; however, research in this population lags behind research in adults. This may be due, in part, to the smaller number of investigators engaged in research with this population and may also be related to changes in safety laws and clinical practice that have altered length of hospital stays, treatment, and access to this population. Specific developmental issues also warrant attention in studies of children, and the ever-changing context of childhood and adolescence may require larger sample sizes than are commonly available to adequately address remaining questions related to TBI. The ENIGMA (Enhancing NeuroImaging Genetics through Meta-Analysis) Pediatric Moderate-Severe TBI (msTBI) group aims to advance research in this area through global collaborative meta-analysis. In this paper we discuss important challenges in pediatric TBI research and opportunities that we believe the ENIGMA Pediatric msTBI group can provide to address them. We conclude with recommendations for future research in this field of study.

EpiPen: An R Package to Investigate Two-Locus Epistatic Models

2014 ◽  
Vol 17 (4) ◽  
Author(s):  
Raymond K. Walters ◽  
Charles Laurin ◽  
Gitta H. Lubke
Keyword(s):  
Power Analysis ◽  
R Package ◽  
Simulation Studies ◽  
Nucleotide Polymorphisms ◽  
Single Nucleotide ◽  
Epistatic Interactions ◽  
Model Interpretation ◽  
Genome Wide ◽  
Using Data ◽  
Power Analyses

Epistasis is a growing area of research in genome-wide studies, but the differences between alternative definitions of epistasis remain a source of confusion for many researchers. One problem is that models for epistasis are presented in a number of formats, some of which have difficult-to-interpret parameters. In addition, the relation between the different models is rarely explained. Existing software for testing epistatic interactions between single-nucleotide polymorphisms (SNPs) does not provide the flexibility to compare the available model parameterizations. For that reason we have developed an R package for investigating epistatic and penetrance models, EpiPen, to aid users who wish to easily compare, interpret, and utilize models for two-locus epistatic interactions. EpiPen facilitates research on SNP-SNP interactions by allowing the R user to easily convert between common parametric forms for two-locus interactions, generate data for simulation studies, and perform power analyses for the selected model with a continuous or dichotomous phenotype. The usefulness of the package for model interpretation and power analysis is illustrated using data on rheumatoid arthritis.

Comparing Instructional Approaches in Caregiver-Implemented Intervention: An Interdisciplinary Systematic Review and Meta-Analysis

2021 ◽  
pp. 105381512198980
Author(s):  
Bailey J. Sone ◽  
Jordan Lee ◽  
Megan Y. Roberts
Keyword(s):  
Adult Learning ◽  
Family Involvement ◽  
Meta Analysis ◽  
Future Research ◽  
Instructional Approaches ◽  
Comparative Efficacy ◽  
Robust Variance ◽  
Analysis Methodology ◽  
Intervention Models ◽  
Variance Estimate

Family involvement is a cornerstone of early intervention (EI). Therefore, positive caregiver outcomes are vital, particularly in caregiver-implemented interventions. As such, caregiver instructional approaches should optimize adult learning. This study investigated the comparative efficacy of coaching and traditional caregiver instruction on caregiver outcomes across EI disciplines. A systematic search for articles was conducted using PRISMA guidelines. Meta-analysis methodology was used to analyze caregiver outcomes, and a robust variance estimate model was used to control for within-study effect size correlations. Seven relevant studies were ultimately included in the analysis. A significant, large effect of coaching on caregiver outcomes was observed compared to other models of instruction ( g = 0.745, SE = 0.125, p = .0013). These results support the adoption of a coaching framework to optimize caregiver outcomes in EI. Future research should examine how coaching and traditional instruction can be used in tiered intervention models with a variety of populations.

scholarly journals Cybersickness in current-generation virtual reality head-mounted displays: systematic review and outlook

2021 ◽  
Author(s):  
Polona Caserman ◽  
Augusto Garcia-Agundez ◽  
Alvar Gámez Zerban ◽  
Stefan Göbel
Keyword(s):  
Systematic Review ◽  
Virtual Reality ◽  
Meta Analysis ◽  
Subjective Evaluation ◽  
Future Research ◽  
Current Generation ◽  
Research Areas ◽  
Head Mounted Displays ◽  
Skin Response ◽  
Golden Standard

AbstractCybersickness (CS) is a term used to refer to symptoms, such as nausea, headache, and dizziness that users experience during or after virtual reality immersion. Initially discovered in flight simulators, commercial virtual reality (VR) head-mounted displays (HMD) of the current generation also seem to cause CS, albeit in a different manner and severity. The goal of this work is to summarize recent literature on CS with modern HMDs, to determine the specificities and profile of immersive VR-caused CS, and to provide an outlook for future research areas. A systematic review was performed on the databases IEEE Xplore, PubMed, ACM, and Scopus from 2013 to 2019 and 49 publications were selected. A summarized text states how different VR HMDs impact CS, how the nature of movement in VR HMDs contributes to CS, and how we can use biosensors to detect CS. The results of the meta-analysis show that although current-generation VR HMDs cause significantly less CS ($$p<0.001$$ p < 0.001 ), some symptoms remain as intense. Further results show that the nature of movement and, in particular, sensory mismatch as well as perceived motion have been the leading cause of CS. We suggest an outlook on future research, including the use of galvanic skin response to evaluate CS in combination with the golden standard (Simulator Sickness Questionnaire, SSQ) as well as an update on the subjective evaluation scores of the SSQ.

scholarly journals Research on the Operating Characteristics of Hydraulic Free-Piston Engines: A Systematic Review and Meta-Analysis

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3530
Author(s):  
Fukang Ma ◽  
Shuanlu Zhang ◽  
Zhenfeng Zhao ◽  
Yifang Wang
Keyword(s):  
Systematic Review ◽  
High Efficiency ◽  
Meta Analysis ◽  
Combustion Process ◽  
Research Progress ◽  
Future Research ◽  
Operating Characteristics ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine

The hydraulic free-piston engine (HFPE) is a kind of hybrid-powered machine which combines the reciprocating piston-type internal combustion engine and the plunger pump as a whole. In recent years, the HFPE has been investigated by a number of research groups worldwide due to its potential advantages of high efficiency, energy savings, reduced emissions and multi-fuel operation. Therefore, our study aimed to assess the operating characteristics, core questions and research progress of HFPEs via a systematic review and meta-analysis. We included operational control, starting characteristics, misfire characteristics, in-cylinder working processes and operating stability. We conducted the literature search using electronic databases. The research on HFPEs has mainly concentrated on four kinds of free-piston engine, according to piston arrangement form: single piston, dual pistons, opposed pistons and four-cylinder complex configuration. HFPE research in China is mainly conducted in Zhejiang University, Tianjin University, Jilin University and the Beijing Institute of Technology. In addition, in China, research has mainly focused on the in-cylinder combustion process while a piston is free by considering in-cylinder combustion machinery and piston dynamics. Regarding future research, it is very important that we solve the instabilities brought about by chance fluctuations in the combustion process, which will involve the hydraulic system’s efficiency, the cyclical variation, the method of predicting instability and the recovery after instability.

scholarly journals Do Commodity Price Shocks Cause Armed Conflict? A Meta-Analysis of Natural Experiments

2021 ◽  
pp. 1-8
Author(s):  
GRAEME BLAIR ◽  
DARIN CHRISTENSEN ◽  
AARON RUDKIN
Keyword(s):  
Causal Effect ◽  
Meta Analysis ◽  
Resource Curse ◽  
Civil Conflict ◽  
Commodity Price ◽  
Future Research ◽  
Natural Experiments ◽  
Price Changes ◽  
Price Increases ◽  
Commodity Price Shocks

Scholars of the resource curse argue that reliance on primary commodities destabilizes governments: price fluctuations generate windfalls or periods of austerity that provoke or intensify civil conflict. Over 350 quantitative studies test this claim, but prominent results point in different directions, making it difficult to discern which results reliably hold across contexts. We conduct a meta-analysis of 46 natural experiments that use difference-in-difference designs to estimate the causal effect of commodity price changes on armed civil conflict. We show that commodity price changes, on average, do not change the likelihood of conflict. However, there are cross-cutting effects by commodity type. In line with theory, we find price increases for labor-intensive agricultural commodities reduce conflict, while increases in the price of oil, a capital-intensive commodity, provoke conflict. We also find that price increases for lootable artisanal minerals provoke conflict. Our meta-analysis consolidates existing evidence, but also highlights opportunities for future research.

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