Improving the rate of classification of patients with the MultidimensionalPain Inventory (MPI): Clarifying the meaning of "significant other"

Objective: The Multidimensional Pain Inventory (MPI) has been used widely t o assess the psychosocial adaptation in chronic pain patients. The MPI can also be used to classify patients into one of three primary subgroups. Howe ver, studies have reported that anywhere from 3% to 30% of patients are unc lassifiable, mostly attributable to an excessive number of missing response s to questions. The purpose of this study was to examine the reasons for th e large number of missing responses and subsequently to reduce the number o f patients who cannot be classified within one of the three primary MPI sub groups. Design: Two Versions of the MPI were evaluated on two samples of patients ( N = 147; and N = 143) with persistent pain being evaluated by the Workers C ompensation Board of British Columbia, Canada. One version used the publish ed MPI instructions and the second modified the instructions to clarify the meaning of the term "significant other." In addition, patients were requir ed to designate a significant other who would serve as the anchor for all r esponses related to a significant other. Results: Approximately 18% of patients could not be classified within one o f the three primary profiles and were determined to be unanalyzable using t he MPI standard classification procedure. Most patients who could not be cl assified had excessive missing data to those questions asking about support received from "significant other." Almost all of these patients with missi ng data were unmarried and living alone. Modifying the instructions of the MPI to specify the meaning of the term "significant other" resulted in an a lmost threefold (6.3% vs, 18%) reduction in the percentage of patients whos e responses could not be analyzed and consequently classified into one of t he three primary MPI subgroups. The revised instructions did nor lead to an y difference in the actual distribution of patients assigned to one of the three profiles. Thus, using the modified instruction did not alter the prop ortion of patients assigned to one of the three primary groups. Conclusion: Modification of the MPI instructions clarifying the definition of a significant other can greatly reduce the, number of patients who are c lassifiable within one of the three primary MPI profiles. Thus, the modifie d instructions of the MPI thence the MPI-M) have a significant advantage ov er the original version. The mean scores on the individual scales of the MP I and the MPI-M are comparable. Moreover, the results demonstrate that the proportion of the previously unanalyzable patients classified within one of the three primary subgroups is comparable to the original proportion of pa tients assigned to each of the primary subgroups. Thus, it may not be neces sary to reestablish the norm scores based on the modified instructions. Fut ure studies and clinicians who wish to use the MPI for the purpose of class ifying patients on the basis of psychosocial and behavioral factors should make use of the MPI-M that incorporates the clarification of the meaning of "significant other.".