Regression to the Mean: Methodological Issues for Evaluation of Heart Rate Variability Variables for Stress Assessment

There is now a substantial body of evidence linking the baseline level of heart rate variability (HRV) with the magnitude of stress-induced reduction in respiratory sinus arrhythmia. However, it remains to be proved to what extent these interindividual differences in stress responses may be attributed to the statistical phenomenon of regression to the mean (RTM). We sought to test the hypothesis that the statistical artifact RTM explains pan of the baseline effect. Heart rate recording was carried out in 1156 volunteers. To obtain an estimate of the stress response. 148 persons were randomly selected. Participants were monitored on a rest day and just before an academic examination for state anxiety and HRV. Participants were divided into quartiles according to baseline HRV levels and were compared for response to academic stress. We observed a significant reduction in HRV in subjects with a high baseline HRV (> 75th percentile), while a significant increase was found in the group with low baseline HRV. Regression analysis demonstrated that the value of baseline HRV correlated with the magnitude of stress reaction consistent with the RTM model. Baseline-adjusted ANCOVA does not reveal significant intergroup differences in the changes hi heart rate (HR) and HRV from rest to exam. RTM-adjusted estimates confirmed an exam effect for HR and HRV. The results of our study strongly support RTM as the source of variability of stress-related changes in HRV.