Department of Psychology, Northumbria University, Newcastle upon Tyne NE1 8ST, United Kingdom.
Am J Hum Biol. 2010 Sep-Oct;22(5):619-30. doi: 10.1002/ajhb.21054.
Our aims are, first, to describe the sex difference in the length ratio of the second and fourth digits (2D:4D), which likely reflects prenatal testosterone levels in humans. Second, to infer the loss of reliability observed in 2D:4D based on self-measured finger lengths.
We used random-effects meta-analysis of 2D:4D based on expert-measured finger lengths (116 samples with 13,260 females and 11,789 males).
We find a moderate sex difference (with lower 2D:4D for males), which shows substantial heterogeneity (which is unrelated to age). The sex difference is moderated by the type of finger length measurement and by hand. Measurement involving the distortion of soft tissue leads to a significantly larger sex difference than finger length measurement avoiding this. The sex difference in 2D:4D is larger in the right hand than in the left. The reliability of self-measured 2D:4D in the BBC internet study, by far the largest study on 2D:4D, is estimated to be 46% of that of expert-measured 2D:4D.
Right-hand 2D:4D might be a better indicator of prenatal androgenisation than left-hand 2D:4D. The view that 2D:4D has allometric properties (Kratochvil L, Flegr J. 2009. Differences in 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line. Biol Lett 5:643-646.) is not supported. Bone lengths contribute to the sex difference in 2D:4D. In addition, there might be a sex difference in fingers' soft tissue, which should be investigated. Because of measurement unreliability, correlations between 2D:4D and variables of interest are about one-third smaller in the BBC internet study than in studies in which 2D:4D is based on expert-measured finger lengths.
我们的目标首先是描述第二和第四指长比（2D:4D）的性别差异，这可能反映了人类产前睾酮水平。其次，根据自我测量的手指长度推断 2D:4D 中观察到的可靠性损失。
我们使用基于专家测量的手指长度的 2D:4D 随机效应荟萃分析（116 个样本，女性 13260 名，男性 11789 名）。
我们发现了一个中等的性别差异（男性的 2D:4D 较低），表现出显著的异质性（与年龄无关）。性别差异受到手指长度测量类型和手的影响。涉及软组织扭曲的测量会导致明显更大的性别差异，而避免这种情况的手指长度测量则不会。右手 2D:4D 的性别差异大于左手。迄今为止最大的 2D:4D 研究——BBC 互联网研究中自我测量的 2D:4D 的可靠性估计为专家测量的 2D:4D 的 46%。
右手 2D:4D 可能是产前雄激素化的更好指标，而左手 2D:4D 则不然。2D:4D 具有同态性质的观点（Kratochvil L，Flegr J. 2009. 人类第二和第四指长比的差异反映了沿着共同同态线的变化。生物信函 5:643-646.）是没有根据的。骨长对 2D:4D 的性别差异有贡献。此外，手指软组织可能存在性别差异，需要进一步研究。由于测量不可靠，与 BBC 互联网研究中 2D:4D 相关的变量之间的相关性比基于专家测量的手指长度的研究中要小三分之一左右。
