The use of the MMPI in identifying personality factors affecting maximum voluntary effort in a chronic low back pain rehabilitation program

The purpose of this study was to investigate the use of the Hypochondriasis (Hs), Depression (D), Hysteria (Hy), and Low Back (Lb) scales on the Minnesota Multiphasic Personality Inventory (MMPI) to predict maximum voluntary effort in a chronic low back pain program as measured by the coefficient of variation achieved during isometric strength testing on Isotechnologies\u27 B-200 back machine. A high coefficient of variation indicates less likelihood of maximum voluntary effort.The coefficient of variation from isometric strength testing on the B-200 served as the dependent variable. This value was established by taking the 4 scores from the isometric strength test, finding their standard deviation, dividing by their mean, and expressing it as a percentage.Stepwise multiple regression was used to evaluate the predictive ability of the MMPI in relationship to the coefficient of variation. The coefficient of variation was the dependent variable while the scores on the Hs, D, Hy, and the Lb scales on the MMPI were independent variables.Subjects were 37 outpatients in a chronic low back pain rehabilitation program, all of whom achieved valid MMPI profiles. They were all worker\u27s compensation patients who were a minimum of 6 months post injury and 3 months post any surgical intervention.Results indicated the Hypochondriasis scale alone to be the best predictor of coefficient of variation. As the Hypochondriasis score increased, the coefficient of variation increased indicating less than maximum voluntary effort. When the Hypochondriasis score was removed and stepwise multiple regression was recalculated, the Hysteria scale became the best predictor.Post hoc analysis using all validity scales, clinical scales, and demographics revealed the Hypochondriasis scale alone to still be the best predictor of the coefficient of variation. When the Hypochondriasis scale was removed this time, the Low Back scale and number of years of education became the best predictors. Years of education negatively correlated with the coefficient of variation