Palmer A Richard
Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
Am J Phys Anthropol. 2002 Jun;118(2):191-9. doi: 10.1002/ajpa.10063.
Evidence for population-level right-handedness in nonhuman primates seems inconsistent and contradictory, and many hypotheses have been advanced to account for this volatility. Funnel plots (scatter plots of percent right-hand use vs. sample size) offer a straightforward graphical technique for assessing: 1) the strength and consistency of handedness, 2) whether variability is consistent with normal sampling variation, and 3) how likely reports of statistically significant handedness might have arisen due to chance (i.e., type I error). They are informative for both within- and among-population variation. Reexamination of within-population variation from a detailed and widely cited study reporting significant population-level right-handedness in 140 individual captive chimpanzees (Hopkins [1994] Dev. Psychobiol. 27:395-407) revealed several puzzling patterns: 1) funnel plots showed higher percent right-hand use among individuals for which fewer observations were recorded, 2) when individuals with fewer than 25 observations were excluded, statistical support for population-level right-handedness either became marginal (P = 0.043, when computed as average percent use of the right hand) or disappeared (P = 0.62, when computed as proportion of individuals using the right hand more than the left, whether they did so significantly or not), and 3) the proportion of statistically ambilateral chimpanzees actually increased with increasing number of observations per individual, rather than decreased as would be expected for true population-level right-handedness. In addition, funnel plots of among-population variation from an earlier meta-analysis (McGrew and Marchant [1997] Yrbk. Phys. Anthropol. 40:201-232) suggested that the four reports of significant right-handedness, out of 37 estimates from 14 studies, were likely those that achieved statistical significance simply due to chance. Funnel plots, and the more refined statistical tests they suggest, confirm that the current evidence for population-level right-handedness in chimpanzees remains equivocal.
非人类灵长类动物群体层面上右利手的证据似乎并不一致且相互矛盾，人们提出了许多假设来解释这种波动性。漏斗图（右手使用百分比与样本量的散点图）提供了一种直观的图形技术，用于评估：1）利手的强度和一致性；2）变异性是否与正常抽样变异一致；3）具有统计学意义的利手报告因偶然因素（即I类错误）出现的可能性有多大。它们对于群体内部和群体之间的变异都具有参考价值。对一项详细且被广泛引用的研究中的群体内部变异进行重新审视，该研究报告了140只圈养黑猩猩存在显著的群体层面右利手现象（霍普金斯[1994]《发展心理生物学》27:395 - 407），发现了几个令人困惑的模式：1）漏斗图显示，记录观察次数较少的个体中右手使用百分比更高；2）当排除观察次数少于25次的个体时，对群体层面右利手的统计支持要么变得微弱（以右手平均使用百分比计算时，P = 0.043），要么消失（以使用右手多于左手的个体比例计算时，P = 0.62，无论他们是否显著地这样做）；3）实际上，统计学上双侧利手的黑猩猩比例随着每个个体观察次数的增加而增加，而不是像真正的群体层面右利手那样减少。此外，早期一项荟萃分析（麦格鲁和马钱特[1997]《体质人类学年度评论》40:201 - 232）中的群体间变异漏斗图表明，在来自14项研究的37个估计值中，有4个显著右利手的报告可能仅仅是由于偶然因素而达到统计学显著性。漏斗图以及它们所建议的更精细的统计检验证实，目前关于黑猩猩群体层面右利手的证据仍然模棱两可。
