Pain measurement scales: a comparison of the visual analogue and faces rating scales in measuring pressure ulcer pain.
OBJECTIVE: Although different pain scales often have been used interchangeably, it is not known whether interchanging them is appropriate. The purpose of this report was twofold: to better understand the statistical properties of the Faces Rating Scale (FRS) so it can be used appropriately in clinical settings and to describe the mathematical relationship between the Visual Analogue Scale (VAS) and the FRS when they are used to quantify pressure ulcer pain in hospitalized elderly patients. DESIGN: Secondary data analyses were performed as part of a cross-sectional study. SETTING AND SUBJECTS: A quality assurance program was undertaken to evaluate pressure ulcer pain perceived by elderly hospitalized patients. All patients without aphasia participated. INSTRUMENTS: The VAS used was a 0 to 100 mm horizontal line demonstrated to have ratio scale properties with high validity and reproducibility, and the FRS used was 6 faces ordered horizontally from smiling to crying, labeled 0 to 5 beneath each face, respectively. METHODS: Nonlinear least squares regression with a Gauss-Newton iterative procedure was used. RESULTS: Among models with cubic, quadratic, and linear terms, only the quadratic term was significant (P <.05). With use of the equation derived, VAS = 3.33*(FRS)(2), the resulting reliability coefficient was r = 0.92. CONCLUSIONS: The nonlinear relationship indicated high reliability between VAS and FRS for pain assessment in populations with diminished verbal and abstract thinking abilities. For readers who would like to translate results from one scale to another, a quadratic equation is provided.