Solidifying fundamental methodological practices of hair cortisol analysis: an investigation into the influence of storage duration, scalp region and sampling method on hair cortisol results

毛发皮质醇分析是一种评估长期累积激素浓度的方法，在生物心理应激研究中得到广泛应用。然而，尽管它很受欢迎，但在毛发皮质醇分析中仍然存在方法论实践的核心方面，目前缺乏任何系统的经验评估。头发皮质醇研究人员经常面临的三个关键问题包括：(i)头发样本在生化分析之前可以保存多久？（ii）头发最好从头皮的哪个部位取样？（iii）所需的头发量是最好从一个更大的样本中提取还是从不同地点收集材料？拟议的项目旨在通过三个精心设计的主题内研究，对这些关键问题进行首次系统调查。研究1使用单个均质毛发材料和分布式采样方案调查了样品储存0、3、6、12或24个月的影响。研究II比较了后顶点和枕部的头发采样，即两个最有希望的头皮区域，而研究III对比了单样本和累积方法之间的数据质量。这三项研究都侧重于(a)内部统计结果（均值和变异性、内部一致性、可靠性）和(b)方法选择对与相关外部标准（人体测量学和生活压力暴露）的关联强度的影响。我们相信这个项目将有助于巩固毛发皮质醇研究的基本实践，从而使研究人员能够做出基于证据的方法选择，提高未来研究的质量。

Hair cortisol analysis is a method for the assessment of long-term cumulative hormone concentrations, which is widely used in biopsychological stress research. However, despite its popularity, there are still central aspects of methodological practices employed in hair cortisol analysis that currently lack any systematic empirical evaluation. Three critical questions that hair cortisol researchers are regularly faced with include: (i) How long can hair samples can be stored before biochemical analysis? (ii) From which area of the scalp should hair best be sampled? And, (iii) is the required amount of hair best derived from a single larger sample or by pooling material from different locations? The proposed project sets out to provide a first systematic investigation into these critical questions by means of three carefully-designed within-subject studies. Study I investigates the influence of sample storage for 0, 3, 6, 12 or 24 months using intra-individually homogenized hair material and a distributed sampling scheme. Study II compares hair sampling from the posterior vertex and the occipital region, i.e. the two most promising scalp areas, while study III contrasts data quality between the single-sample vs. the accumulation method. Each of the three studies focuses on (a) internal statistical outcomes (means and variability, internal consistency, reliability) and (b) the impact of methodological choices on strength of association with relevant external criteria (anthropometrics and life stress exposure). We believe that this project will help solidify fundamental practices of hair cortisol research, thus allowing researchers to make evidence-based methodological choices and improving the quality of future research.