Which statement best summarizes the focus of Dr. Johnson's research?

The statement about examining heart rate variability as a stable trait over time accurately reflects a focus on understanding heart rate variability not just as a momentary measure, but as a consistent characteristic that can offer insights into an individual's physiological and psychological state throughout different contexts. This focus suggests an interest in the broader implications of heart rate variability, such as how it may relate to stress, emotion regulation, or other psychological constructs over time rather than just during specific circumstances.

In contrast, other options delve into different areas of research. Investigating the impact of stress on psychology would be focused more on the psychological aspects without emphasizing heart rate variability specifically. Studying the effects of exercise on heart health primarily emphasizes physical health outcomes rather than the nuanced, trait-based perspective of heart rate variability. Exploring the relationship between anxiety and heart rate could relate to changes in heart rate during states of anxiety but does not consider the stable traits and long-term aspects that are central to the focus of Dr. Johnson's research on heart rate variability.