Factor Analysis of New Symptom Scale in Breast Cancer Finds Six Clusters

WAYNE, NJ—Initial testing of the Symptom Experience Scale (SES), designed to measure women's experiences of symptoms associated with treatment for breast cancer, found six factors that used all 24 SES items and accounted for 83% of the variance, report Nelda Samarel, EdD, RN, of William Paterson College of New Jersey, and her colleagues.

The six factors were nausea and appetite, fatigue and sleep, concentration, appearance, bowel pattern, and pain.

The SES is a modification of McCorkle's Symptom Distress Scale, which was designed to measure symptoms of distress in patients with chronic illness. The measurement of symptoms is important, Dr. Samarel says (citing McCorkle) "to assess patients' needs, determine the effectiveness of nursing interventions targeted to symptom management, and assist patients in monitoring their own levels of health."

The SES measures the frequency, intensity, and distress of eight symptoms (nausea, pain, appetite disturbance, sleep disturbance, fatigue, changes in bowel pattern, concentration disturbance, and changes in appearance), for a total of 24 items. It was tested in a sample of 252 women with breast cancer.

Factor analysis was used to explore the underlying structure of the symptom experience, Dr. Samarel says. The researchers expected to find three factors, representing the three dimensions (frequency, intensity, distress), for each symptom. However, a forced three-factor solution produced conceptually confusing clusters of symptoms.

This led the team to seek a mathematical solution, which yielded six clusters of symptoms (J Pain Symptom Manage 12:221-228, 1996). Rather than the three dimensions, the actual factor structure was the symptoms themselves, the authors note, with the dimensions of the symptoms as components of each factor.

"These findings indicate that the three dimensions of the symptom experience are equally important. By measuring all three dimension, researchers and clinicians should be able to target interventions to a specific aspect of a symptom or symptom cluster," Dr. Samarel says.

The authors conclude that the SES is a useful instrument for assessing symptoms associated with treatment for breast cancer, but recommend further research to determine the stability of the six-factor structure identified in their report.