scholarly journals Standardized mean differences cause funnel plot distortion in publication bias assessments

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Peter-Paul Zwetsloot ◽  
Mira Van Der Naald ◽  
Emily S Sena ◽  
David W Howells ◽  
Joanna IntHout ◽  
...  
Keyword(s):  
Sample Size ◽  
Publication Bias ◽  
Small Sample Size ◽  
Small Sample ◽  
Mean Difference ◽  
Funnel Plot ◽  
Funnel Plots ◽  
Mean Differences ◽  
Meta Analyses ◽  
Positive Results

Meta-analyses are increasingly used for synthesis of evidence from biomedical research, and often include an assessment of publication bias based on visual or analytical detection of asymmetry in funnel plots. We studied the influence of different normalisation approaches, sample size and intervention effects on funnel plot asymmetry, using empirical datasets and illustrative simulations. We found that funnel plots of the Standardized Mean Difference (SMD) plotted against the standard error (SE) are susceptible to distortion, leading to overestimation of the existence and extent of publication bias. Distortion was more severe when the primary studies had a small sample size and when an intervention effect was present. We show that using the Normalised Mean Difference measure as effect size (when possible), or plotting the SMD against a sample size-based precision estimate, are more reliable alternatives. We conclude that funnel plots using the SMD in combination with the SE are unsuitable for publication bias assessments and can lead to false-positive results.

scholarly journals Replication and contradiction of highly cited research papers in psychiatry: 10-year follow-up

2015 ◽  
Vol 207 (4) ◽  
pp. 357-362 ◽  
Author(s):  
Aran Tajika ◽  
Yusuke Ogawa ◽  
Nozomi Takeshima ◽  
Yu Hayasaka ◽  
Toshi A. Furukawa
Keyword(s):  
Sample Size ◽  
Small Sample Size ◽  
Total Sample ◽  
Small Sample ◽  
Research Papers ◽  
Effective Interventions ◽  
Mean Differences ◽  
Larger Sample ◽  
Highly Cited

BackgroundContradictions and initial overestimates are not unusual among highly cited studies. However, this issue has not been researched in psychiatry.AimsTo assess how highly cited studies in psychiatry are replicated by subsequent studies.MethodWe selected highly cited studies claiming effective psychiatric treatments in the years 2000 through 2002. For each of these studies we searched for subsequent studies with a better-controlled design, or with a similar design but a larger sample.ResultsAmong 83 articles recommending effective interventions, 40 had not been subject to any attempt at replication, 16 were contradicted, 11 were found to have substantially smaller effects and only 16 were replicated. The standardised mean differences of the initial studies were overestimated by 132%. Studies with a total sample size of 100 or more tended to produce replicable results.ConclusionsCaution is needed when a study with a small sample size reports a large effect.

scholarly journals Prevalence of overweight/obesity among the adult population in Ethiopia: a systematic review and meta-analysis

BMJ Open ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. e039200
Author(s):  
Ayelign Mengesha Kassie ◽  
Biruk Beletew Abate ◽  
Mesfin Wudu Kassaw
Keyword(s):  
Systematic Review ◽  
Sample Size ◽  
Publication Bias ◽  
Small Sample Size ◽  
Meta Analysis ◽  
Overweight And Obesity ◽  
Small Sample ◽  
Urban Settings ◽  
Pooled Prevalence ◽  
Prevalence Of Obesity

BackgroundOverweight and obesity are emerging public health problems in Ethiopia. However, primary study findings on the prevalence of overweight and obesity in Ethiopia are inconsistent. Therefore, this study aimed to estimate the pooled prevalence of overweight and obesity among adults in Ethiopia.MethodsStudies that looked at overweight and obesity among adults were searched from four international databases. The search involved articles published from 1 January 2010 to 10 March 2020. The Cochran’s Q χ2 and the I2 test statistics were used to check heterogeneity among the studies. The funnel plot and Egger’s regression tests were also used to assess the presence of publication bias. Subgroup analysis was performed by residence, study setting, sample size and year of study. Sensitivity analysis was also done to assess the effect of a single study on the pooled estimates. Data analysis was done using STATA V.14 software program.ResultsA total of 16 studies with 19 527 study participants were included in this systematic review and meta-analysis. The estimated pooled prevalence of overweight among adults in Ethiopia was 20.4%, and after adjustment for publication bias with the trim-and-fill analysis, the estimated prevalence rate was changed to 19%. Besides, the estimated pooled prevalence of obesity was 5.4%. The prevalence of overweight was higher, 22.6% in studies published since 2015, 22.4% in studies conducted only in urban settings and 24.4% in studies with small sample size (≤384 participants). Similarly, the prevalence of obesity was 6.9% in studies published since 2015, 6.2% in studies conducted only in urban settings, 6.4% in institution-based settings and 9.6% in studies with small sample size.ConclusionThe prevalence of overweight and obesity is high in Ethiopia compared with previous studies. This needs large scale awareness creation campaigns and situation-based and context-specific prevention strategies.

scholarly journals Ozone Therapy: two projects of treatment in Vietnam population for back pain and stroke [abstract]

2019 ◽  
Vol 3 (4) ◽  
Author(s):  
Lorenzo Stangoni ◽  
Nguyen Thi-Hoa ◽  
Trinh Duy-Thang
Keyword(s):  
Low Back Pain ◽  
Back Pain ◽  
Sample Size ◽  
Small Sample Size ◽  
Small Sample ◽  
Low Back ◽  
Ozone Therapy ◽  
Traditional Treatment ◽  
Primary Evaluation ◽  
Positive Results

INTRODUCTION: Here we show the results of two clinical projects carried out in Vietnamese patients suffering from low back pain or stroke aftermath comparing with our protocols with and without ozone therapy. MATERIAL and METHODS: We did a first evaluation (project 1 - 179 patients) of adding ozone therapy in our protocols for low back pain and stroke aftermath. After realizing of the positive results, we started the second proyect (207 patients), comparing directly our old and new protocols that include ozone therapy. The treatment from low back pain were executed with classical paraverteberal injections of ozone. The treatment of stroke were executed with intramuscular injections of ozone in the affected area. RESULTS: Comparing with our traditional treatment methods, ozone can improve the speed and the efficacy of the treatment. CONCLUSION: Due to the small sample size, the results has limitations. However the primary evaluation is a reference which requires to have better collaboration with other physicians in order to increase the sample size and validite strongly this technique.

Power-Enhanced Funnel Plots for Meta-Analysis

2020 ◽  
Vol 228 (1) ◽  
pp. 43-49 ◽  
Author(s):  
Michael Kossmeier ◽  
Ulrich S. Tran ◽  
Martin Voracek
Keyword(s):  
Statistical Power ◽  
Meta Analysis ◽  
Relevant Information ◽  
Selective Reporting ◽  
Graphical Display ◽  
Funnel Plot ◽  
Evidential Value ◽  
Graphical Displays ◽  
Funnel Plots ◽  
Meta Analyses

Abstract. Currently, dedicated graphical displays to depict study-level statistical power in the context of meta-analysis are unavailable. Here, we introduce the sunset (power-enhanced) funnel plot to visualize this relevant information for assessing the credibility, or evidential value, of a set of studies. The sunset funnel plot highlights the statistical power of primary studies to detect an underlying true effect of interest in the well-known funnel display with color-coded power regions and a second power axis. This graphical display allows meta-analysts to incorporate power considerations into classic funnel plot assessments of small-study effects. Nominally significant, but low-powered, studies might be seen as less credible and as more likely being affected by selective reporting. We exemplify the application of the sunset funnel plot with two published meta-analyses from medicine and psychology. Software to create this variation of the funnel plot is provided via a tailored R function. In conclusion, the sunset (power-enhanced) funnel plot is a novel and useful graphical display to critically examine and to present study-level power in the context of meta-analysis.

Application of Ultrasound Elastography for Assessing Intestinal Fibrosis in Inflammatory Bowel Disease: Fiction or Reality?

2020 ◽  
Vol 21 ◽  
Author(s):  
Roberto Gabbiadini ◽  
Eirini Zacharopoulou ◽  
Federica Furfaro ◽  
Vincenzo Craviotto ◽  
Alessandra Zilli ◽  
...  
Keyword(s):  
Inflammatory Bowel Disease ◽  
Sample Size ◽  
Bowel Disease ◽  
Small Sample Size ◽  
Shear Wave Elastography ◽  
Small Sample ◽  
Ultrasound Elastography ◽  
Invasive Technique ◽  
Intestinal Fibrosis ◽  
Inflammatory Bowel

Background: Intestinal fibrosis and subsequent strictures represent an important burden in inflammatory bowel disease (IBD). The detection and evaluation of the degree of fibrosis in stricturing Crohn’s disease (CD) is important to address the best therapeutic strategy (medical anti-inflammatory therapy, endoscopic dilation, surgery). Ultrasound elastography (USE) is a non-invasive technique that has been proposed in the field of IBD for evaluating intestinal stiffness as a biomarker of intestinal fibrosis. Objective: The aim of this review is to discuss the ability and current role of ultrasound elastography in the assessment of intestinal fibrosis. Results and Conclusion: Data on USE in IBD are provided by pilot and proof-of-concept studies with small sample size. The first type of USE investigated was strain elastography, while shear wave elastography has been introduced lately. Despite the heterogeneity of the methods of the studies, USE has been proven to be able to assess intestinal fibrosis in patients with stricturing CD. However, before introducing this technique in current practice, further studies with larger sample size and homogeneous parameters, testing reproducibility, and identification of validated cut-off values are needed.

scholarly journals Confirming known planetary trends using a photometrically selected Kepler sample

2020 ◽  
Author(s):  
Jonah T Hansen ◽  
Luca Casagrande ◽  
Michael J Ireland ◽  
Jane Lin
Keyword(s):  
Sample Size ◽  
Robust Statistics ◽  
Narrow Band ◽  
Small Sample Size ◽  
Small Sample ◽  
Fitting Algorithm ◽  
Statistical Studies ◽  
The Rich ◽  
Host Stars ◽  
High Metallicity

Abstract Statistical studies of exoplanets and the properties of their host stars have been critical to informing models of planet formation. Numerous trends have arisen in particular from the rich Kepler dataset, including that exoplanets are more likely to be found around stars with a high metallicity and the presence of a “gap” in the distribution of planetary radii at 1.9 R⊕. Here we present a new analysis on the Kepler field, using the APOGEE spectroscopic survey to build a metallicity calibration based on Gaia, 2MASS and Strömgren photometry. This calibration, along with masses and radii derived from a Bayesian isochrone fitting algorithm, is used to test a number of these trends with unbiased, photometrically derived parameters, albeit with a smaller sample size in comparison to recent studies. We recover that planets are more frequently found around higher metallicity stars; over the entire sample, planetary frequencies are 0.88 ± 0.12 percent for [Fe/H] < 0 and 1.37 ± 0.16 percent for [Fe/H] ≥ 0 but at two sigma we find that the size of exoplanets influences the strength of this trend. We also recover the planet radius gap, along with a slight positive correlation with stellar mass. We conclude that this method shows promise to derive robust statistics of exoplanets. We also remark that spectrophotometry from Gaia DR3 will have an effective resolution similar to narrow band filters and allow to overcome the small sample size inherent in this study.

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