Whether to measure change from baseline or absolute level in studies of children's cardiovascular reactivity: a two-year follow-up.

Blood pressure and heart rate were measured at rest and during a television video game in 399 healthy children. At the first assessment, children were in third grade and at the 2-year follow-up, they were in fifth grade. Children were classified according to race (black/white), gender (boy/girl), body mass index (light/heavy), and video game performance (low score/high score). Correlational analysis indicated that irrespective of the classification variable, absolute reactivity values, e.g., a heart rate of 110 bpm, tended to be more stable than change reactivity values, e.g., a heart rate change of 10 bpm. The greater stability of absolute values was most pronounced with systolic blood pressure. Absolute values were at least as stable as resting values and frequently demonstrated greater stability. Mean and maximal reactivities were correlated comparably. We conclude that children's reactivity is a stable characteristic and that, unless indicated by a priori hypotheses, the use of absolute values is preferable to the use of change values.