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D Grove - One of the best experts on this subject based on the ideXlab platform.
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Use of the mann whitney U Test for clUstered data
Statistics in Medicine, 1999Co-Authors: Bernard Rosner, D GroveAbstract:The Mann-Whitney U-Test is UbiqUitoUs in statistical practice for the comparison of measUres of location for two samples where the assUmption of normality is qUestionable. FreqUently, one has replicate data for each individUal in a groUp and woUld like to compare measUres of central tendency between groUps withoUt assUming normality. For this pUrpose, we present a generalization of the Mann-Whitney U-Test for clUstered data. The Test is performed by compUting zc = (Wc - mU c)/sigma c, approximately N(0, 1) Under H0, where Wc, mU c are the observed and expected Mann-Whitney U-statistic based on a comparison of all pairs of replicates in the two groUps and sigma c is the standard deviation of Wc that is modified to accoUnt for clUstering effects within a clUster. We obtain an explicit variance formUla that is a fUnction of foUr clUstering parameters. We validate the properties of the Test procedUre in a simUlation stUdy. We illUstrate the methods with an example comparing the baseline HUmphrey visUal field between two treatment groUps in a randomized clinical trial of patients with retinitis pigmentosa (RP).
Graeme D. Ruxton - One of the best experts on this subject based on the ideXlab platform.
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the UneqUal variance t Test is an UnderUsed alternative to stUdent s t Test and the mann whitney U Test
Behavioral Ecology, 2006Co-Authors: Graeme D. RuxtonAbstract:Often in the stUdy of behavioral ecology, and more widely in science, we reqUire to statistically Test whether the central tendencies (mean or median) of 2 groUps are different from each other on the basis of samples of the 2 groUps. In sUrveying recent issUes of Behavioral Ecology (VolUme 16, issUes 1–5), I foUnd that, of the 130 papers, 33 (25%) Used at least one statistical comparison of this sort. Three different Tests were Used to make this comparison: StUdent’s t-Test (67 occasions; 26 papers), Mann–Whitney U Test (43 occasions; 21 papers), and the t-Test for UneqUal variances (9 occasions; 4 papers). My aim in this forUm article is to argUe for the greater Use of the last of these Tests. The nUmbers jUst related sUggest that this Test is not commonly Used. In my sUrvey, I was able to identify Tests described simply as ‘‘t-Tests’’ with confidence as either a StUdent’s t-Test or an UneqUal variance t-Test becaUse the calcUlation of degrees of freedom from the 2 sample sizes is different for the 2 Tests (see below). Hence, the neglect of the UneqUal variance t-Test illUstrated above is a real phenomenon and can be explained in several (nonexclUsive ways) ways: 1. AUthors are Unaware that StUdent’s t-Test is Unreliable
Juan M Garciagomez - One of the best experts on this subject based on the ideXlab platform.
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higher vascUlarity at infiltrated peripheral edema differentiates proneUral glioblastoma sUbtype
bioRxiv, 2020Co-Authors: Eduard Chelebian, Elies Fustergarcia, Maria Del Mar Alvareztorres, Javier Juanalbarracin, Juan M GarciagomezAbstract:BACKGROUND AND PURPOSE: Genetic classifications are crUcial for Understanding the heterogeneity of glioblastoma. Recently, MR perfUsion imaging techniqUes have demonstrated their ability to determine molecUlar alterations. In this work, we investigated whether perfUsion markers within infiltrated peripheral edema were associated with proneUral, mesenchymal, classical and neUral sUbtypes. MATERIALS AND METHODS: ONCOhabitats open web service was Used to obtain the cerebral blood volUme at the infiltrated peripheral edema for MRI stUdies of 50 glioblastoma patients from The Cancer Imaging Archive: TCGA-GBM. ANOVA and KrUskal-Wallis Tests were carried oUt in order to assess the association between vascUlar featUres and the sUbtypes. For assessing specific differences, Mann-Whitney U-Test was condUcted. Finally, the association of overall sUrvival with molecUlar and vascUlar featUres was assessed Using Univariate and mUltivariate Cox models. RESULTS: ANOVA and KrUskal-Wallis Tests for the maximUm cerebral blood volUme at the infiltrated peripheral edema between the foUr sUbclasses yielded false discovery rate corrected p-valUes of <0.001 and 0.02, respectively. This vascUlar featUre was significantly higher (p=0.002) in proneUral patients compared to the rest of the sUbtypes while condUcting Mann-Whitney U-Test. The mUltivariate Cox model pointed to redUndant information provided by vascUlar featUres at the peripheral edema and proneUral sUbtype when analyzing overall sUrvival. CONCLUSIONS: Higher relative cerebral blood volUme at infiltrated peripheral edema is associated with proneUral glioblastoma sUbtype sUggesting Underlying vascUlar behavior related to molecUlar composition in that area.
Garcia-gomez, Juan M. - One of the best experts on this subject based on the ideXlab platform.
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Higher vascUlarity at infiltrated peripheral edema differentiates proneUral glioblastoma sUbtype
'Public Library of Science (PLoS)', 2020Co-Authors: Chelebian Eduard, Fuster-garcia Elies, Alvarez-torres, Maria Del Mar, Juan-albarracin Javier, Garcia-gomez, Juan M.Abstract:BackgroUnd and pUrpose Genetic classifications are crUcial for Understanding the heterogeneity of glioblastoma. Recently, perfUsion MRI techniqUes have demonstrated associations molecUlar alterations. In this work, we investigated whether perfUsion markers within infiltrated peripheral edema were associated with proneUral, mesenchymal, classical and neUral sUbtypes. Materials and methods ONCOhabitats open web services were Used to obtain the cerebral blood volUme at the infiltrated peripheral edema for MRI stUdies of 50 glioblastoma patients from The Cancer Imaging Archive: TCGA-GBM. ANOVA and KrUskal-Wallis Tests were carried oUt in order to assess the association between vascUlar featUres and the Verhaak sUbtypes. For assessing specific differences, Mann-Whitney U-Test was condUcted. Finally, the association of overall sUrvival with molecUlar and vascUlar featUres was assessed Using Univariate and mUltivariate Cox models. ResUlts ANOVA and KrUskal-Wallis Tests for the maximUm cerebral blood volUme at the infiltrated peripheral edema between the foUr sUbclasses yielded false discovery rate corrected p-valUes of <0.001 and 0.02, respectively. This vascUlar featUre was significantly higher (p = 0.0043) in proneUral patients compared to the rest of the sUbtypes while condUcting Mann-Whitney U-Test. The mUltivariate Cox model pointed to redUndant information provided by vascUlar featUres at the peripheral edema and proneUral sUbtype when analyzing overall sUrvival. ConclUsions Higher relative cerebral blood volUme at infiltrated peripheral edema is associated with proneUral glioblastoma sUbtype sUggesting Underlying vascUlar behavior related to molecUlar composition in that area
Bernard Rosner - One of the best experts on this subject based on the ideXlab platform.
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Assessing discrimination of risk prediction rUles in a clUstered data setting
Lifetime data analysis, 2012Co-Authors: Bernard Rosner, Weiliang Qiu, Mei-ling Ting LeeAbstract:The AUC (area Under ROC cUrve) is a commonly Used metric to assess discrimination of risk prediction rUles; however, standard errors of AUC are UsUally based on the Mann–Whitney U Test that assUmes independence of sampling Units. For ophthalmologic applications, it is desirable to assess risk prediction rUles based on eye-specific oUtcome variables which are generally highly, bUt not perfectly correlated in fellow eyes [e.g. progression of individUal eyes to age-related macUlar degeneration (AMD)]. In this article, we Use the extended Mann–Whitney U Test (Rosner and Glynn, Biometrics 65:188–197, 2009) for the case where sUbUnits within a clUster may have different progression statUs and assess discrimination of different prediction rUles in this setting. Both data analyses based on progression of AMD and simUlation stUdies show reasonable accUracy of this extended Mann–Whitney U Test to assess discrimination of eye-specific risk prediction rUles.
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Use of the mann whitney U Test for clUstered data
Statistics in Medicine, 1999Co-Authors: Bernard Rosner, D GroveAbstract:The Mann-Whitney U-Test is UbiqUitoUs in statistical practice for the comparison of measUres of location for two samples where the assUmption of normality is qUestionable. FreqUently, one has replicate data for each individUal in a groUp and woUld like to compare measUres of central tendency between groUps withoUt assUming normality. For this pUrpose, we present a generalization of the Mann-Whitney U-Test for clUstered data. The Test is performed by compUting zc = (Wc - mU c)/sigma c, approximately N(0, 1) Under H0, where Wc, mU c are the observed and expected Mann-Whitney U-statistic based on a comparison of all pairs of replicates in the two groUps and sigma c is the standard deviation of Wc that is modified to accoUnt for clUstering effects within a clUster. We obtain an explicit variance formUla that is a fUnction of foUr clUstering parameters. We validate the properties of the Test procedUre in a simUlation stUdy. We illUstrate the methods with an example comparing the baseline HUmphrey visUal field between two treatment groUps in a randomized clinical trial of patients with retinitis pigmentosa (RP).
