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When is enough, enough? Questions of sampling in vertebrate ichnology
Palaeontology ( IF 2.6 ) Pub Date : 2021-07-16 , DOI: 10.1111/pala.12566
Matteo Belvedere 1, 2 , Marcin Budka 1 , Ashleigh L. A. Wiseman 3 , Matthew R. Bennett 1
Affiliation  

Sample size is a challenge for most field scientists determined not by the statistically ideal, but by the available. In vertebrate ichnology, track length is an important variable correlating well with the track-maker’s biology. It is also key to estimating the minimum number of individuals (MNI) present on a trampled horizon. Broad assumptions on biometrics of the track-makers are often made based on a few prints without consideration for intra-trackway variability. In this study we use a simple bootstrapping algorithm to explore variance within sample size for a range of trackways with fossil and experimental examples to determine the minimum sample size required to extract linear measurements. Predictably, experimentation shows that inter-step variability changes with track-maker and substrate, but the degree of variance is not as marked as previously anticipated. Change-point modelling suggests that a maximum sample size of 22–25 captures most of the variance present in track length at least; another threshold at 7–10 has been identified, which represents the reasonable sample size minimum. Samples of fewer than seven tracks are subject to large amounts of potential variance and are unlikely to provide reliable and consistent measurements. These sampling thresholds hold across a wide range of depositional environments and track-makers. We calculate generic standard errors for human track-makers which may assist the practitioner with small samples to estimate the likely errors, especially when making MNI estimates. The challenge is placed to the wider vertebrate ichnology to explore this issue for other track-makers and develop similar guidance.

中文翻译:

什么时候够,够了?脊椎动物物种学中的抽样问题

对于大多数现场科学家来说,样本量是一个挑战,不是由统计上的理想决定的,而是由可用的数据决定的。在脊椎动物物种学中,轨迹长度是一个与轨迹制造者的生物学密切相关的重要变量。估计被践踏的地平线上的最小个体数 (MNI) 也是关键。对赛道制造者生物特征的广泛假设通常是基于一些印刷品而不考虑赛道内的可变性。在这项研究中,我们使用简单的引导算法来探索一系列具有化石和实验示例的轨道的样本大小内的方差,以确定提取线性测量所需的最小样本大小。可以预见的是,实验表明步骤间的可变性会随着轨道制造商和基材的变化而变化,但差异程度并不像之前预期的那样明显。变化点建模表明,22-25 的最大样本量至少捕获了轨道长度中存在的大部分差异;另一个阈值 7-10 已被确定,它代表了合理的最小样本量。少于七个轨道的样本会受到大量潜在差异的影响,并且不太可能提供可靠且一致的测量结果。这些采样阈值适用于范围广泛的沉积环境和跟踪器。我们计算人类追踪者的通用标准误差,这可以帮助从业者使用小样本来估计可能的误差,尤其是在进行 MNI 估计时。
更新日期:2021-08-17
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