Answer:
Psychobiological reactivity to stress.
Explanation:
As the exercise details, what . Cohen and colleagues suggested was that psychobiological reactivity to stress is an important factor that influences the stress-illness relationship. We, as individuals, respond differently when exposed to the same stressor. Such differences can be observed in all four major stress response domains, namely, physiology, behavior, subjective experience, and cognitive function. So, to try this, S. Cohen must have tested different individuals with the same stressor to see how they responded, hence proving that the psychobiological reactivity to stress is an important factor.