One study suggests that there is a correlation between a negative life event and the onset of CFS. Researchers interviewed 46 CFS patients with a mean age of 39.5 years and matched them with referents. Both the referent and the patients were given a list of 14 different life events and asked to identify any which were experienced in proceeding months. They also rated the importance of the events experienced and the intensity of CFS symptoms for each proceeding month. Sixty-seven percent of the referents and the patients had a negative life event (spouse conflict, conflict with a close friend or relative, illness or accident in spouse, death of spouse, death of close relative or friend, financial problems, or conflict in the workplace) occur during the year proceeding CFS onset. The negative life events caused a rise in fatigue of both groups. The level of fatigue was higher during the crisis for CFS patients and remained with the patient longer than it did with the referents. Sadness was not different among the groups proceeding the crisis but the level stayed high for patients while the level slowly returned for the referents in the year after the crisis.