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Classification based hypothesis testing in neuroscience: Below‐chance level classification rates and overlooked statistical properties of linear parametric classifiers

机译:神经科学中基于分类的假设检验:低于机会水平的分类率和线性参数分类器的被忽略的统计特性

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摘要

Multivariate pattern analysis (MVPA) has recently become a popular tool for data analysis. Often, classification accuracy as quantified by correct classification rate (CCR) is used to illustrate the size of the effect under investigation. However, we show that in low sample size (LSS), low effect size (LES) data, which is typical in neuroscience, the distribution of CCRs from cross‐validation of linear MVPA is asymmetric and can show classification rates considerably below what would be expected from chance classification. Conversely, the mode of the distribution in these cases is above expected chance levels, leading to a spuriously high number of above chance CCRs. This unexpected distribution has strong implications when using MVPA for hypothesis testing. Our analyses warrant the conclusion that CCRs do not well reflect the size of the effect under investigation. Moreover, the skewness of the null‐distribution precludes the use of many standard parametric tests to assess significance of CCRs. We propose that MVPA results should be reported in terms of values, which are estimated using randomization tests. Also, our results show that cross‐validation procedures using a low number of folds, e.g. twofold, are generally more sensitive, even though the average CCRs are often considerably lower than those obtained using a higher number of folds. . © .
机译:多元模式分析(MVPA)最近已成为流行的数据分析工具。通常,使用正确分类率(CCR)量化的分类精度来说明所研究效果的大小。但是,我们表明,在神经科学中很典型的低样本量(LSS)和低效应量(LES)数据中,线性MVPA的交叉验证产生的CCR分布是不对称的,并且可以显示出明显低于分类值的分类率。从机会分类中期望。相反,在这些情况下的分布方式高于预期机会水平,导致虚假数量高的机会超过CCR。当使用MVPA进行假设检验时,这种意外的分布具有很强的含义。我们的分析可以得出以下结论:CCR不能很好地反映所研究效应的大小。此外,由于零分布的偏斜性,无法使用许多标准参数测试来评估CCR的重要性。我们建议,MVPA结果应以值报告,该值是使用随机化测试估算的。此外,我们的结果表明,交叉验证程序使用的折叠次数较少,例如即使平均CCR通常通常比使用较高倍数获得的CCR低很多,但通常情况下,它们的敏感性通常更高。 。 ©。

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