General studies on the effects of perceived control
Cohen et al (1993) used the viral-challenge technique to study the effects of stress on more than 400 volunteers. Individuals were divided into an experimental group (who were given nasal drops containing the common cold virus) and a control group (who received harmless nasal drops). All participants completed a questionnaire to assess their levels of perceived stress. Cohen et al found a positive correlation between levels of stress and likelihood of catching a cold. In particular, those participants who felt their lives were unpredictable and uncontrollable were twice as likely to develop colds as those suffering low stress.
Schulz (1976) randomly assigned institutionalised elderly people to one of four conditions. Participants in the first group could determine both the frequency and duration of visits…