Physiometrics in Salivary Bioscience

Background: Accurate estimation in statistical models depends on sample size but also, critically, reliability of the measure. Physiometrics is the equivalent of psychometrics for measures such as sex hormones, catabolic hormones, and products of the immune system. Method: There are multiple ways to measure physiometrics, from simple correlation to complex generalizability theory designs. Depending on the design, these estimates can provide information about equivalency (e.g., the correlation between two measurements taken close together in time) or stability (e.g., the correlation between two measurements taken farther apart in time). Results: The physiometrics of salivary measures including cortisol, α-amylase, testosterone, and cytokines range from highly stable, requiring only a single sample, to highly unstable, requiring multiple samples to achieve generalizability to longer periods of time. However, generalizability is relative to the study design, and only some designs call for stable and generalizable measures. Conclusion: Both dedicated physiometric studies and more reporting of physiometrics in psychoneuroendocrinology and psychoneuroimmunology will improve the quality of salivary bioscience study designs in the future.