Baselines Matter: Cardiovascular Baseline Procedures in Affective Psychophysiology

A baseline is necessary to define biological reactivity in psychophysiological research. However, the conceptualization and implementation of baseline measurements are often underdescribed and weakly justified. This poses a problem because poor baseline decisions have the potential to introduce noise, reduce comparability across studies, and bias interpretations of data. In this article, we focus on laboratory studies using cardiovascular measures to examine how baselines are described and used in affective psychophysiology. To describe heterogeneity in baseline procedures, Study 1 reviewed 310 psychophysiological studies and coded baseline activities, durations, analyzed intervals, and theoretical justifications. To examine within-baseline stabilization, Study 2 analyzed the POPANE dataset to assess minute-by-minute changes in cardiovascular activity in 1,010 participants during a standard 5-minute baseline. To test whether these patterns replicated and whether baseline estimates differed across sessions, Study 3 analyzed the CEPAV dataset in 300 participants across two separate laboratory visits. Finally, to assess generalizability across a larger and more heterogeneous sample, Study 4 replicated these analyses using compiled laboratory data from 2,395 participants. Across studies, results indicate that baseline procedures vary considerably, are often insufficiently reported, and may meaningfully impact the interpretation of cardiovascular data. Although different cardiovascular indices may stabilize differently during a 5-minute baseline, findings suggest that this procedure is a reasonable, pragmatic choice and that separate-session baselines should not be assumed to be superior. More broadly, findings highlight the need for stronger justification, standardization, and reporting of baseline procedures in psychophysiological research.