... established criteria for validity, reliability and responsiveness. Factor analysis showedthat SAPS and fatigue contributed most, and respectivelyexplained 47.4% and 31.2% of the variance; sleep ... was directly attributable to the presence of chronic pain (because of the possibility of confounding var- iables such as comorbidity or the fact that pain may be a sec-ondary symptom of another ... sleepdisturbances, psychological and cognitive alterations, head-ache, migraine, variable bowel habits, diffuse abdominal pain, and urinary frequency [1-3], which is why studies have used awide variety of outcome...