To determine the metric properties of the WOMAC questionnaire filled in over the telephone; and to obtain a reduced version of this questionnaire.
Descriptive study.
"La Merced" (Osuna. Seville) and "Torrecárdenas" (Almeria) Hospitals.
People suffering from hip and knee osteoarthritis and awaiting surgical intervention from October 2004 to November 2006.
Telephone interview, sociodemographic variables and Symptoms and Physical Functional Disability (WOMAC questionnaire) were collected.
A total of 311 people suffering from hip or knee osteoarthritis were included. Subjects were mostly women (82.63%) with a mean age of 70 years. Metric properties of the original and reduced WOMAC were as follows: All WOMAC items obtained a maximum value of 67.4% on endorsement frequency. Main components factorial analysis resulted in a communality of over 0.5 and 71.73% of total explained variance, with 5 factors -no conceptual meaning-. With a communality cut-off point of 0.8; 13 items were rejected and the total explained variance increased to 87.74% with 4 factors -conceptually sensible-. Varimax rotations were performed due to low correlation factors. Pearson correlation between the original and reduced WOMAC versions were 0.92. Reliability analysis obtained a Cronbach alpha value of 0.92 for original WOMAC and 0.82 for the reduced version.
The original WOMAC questionnaire showed adequate metric properties to be used over the telephone on people suffering from hip and knee osteoarthritis. Furthermore, a reduced version of WOMAC with 11 items had better metric properties than the full version.