Clinically significant and practical! Enhancing precision does make a difference. Reply to McGlinchey and Jacobson, Hsu, and Speer

Based on a secondary analysis of the Jacobson and Truax [Jacobson, N.S. & T ruax, P. (1991). Clinical significance: a statistical approach to defining meaningful change in psychotherapy research. Journal of Consulting and Clin ical Psychology, 59, 12-19.] data using both their own traditional approach and the refined method advanced by Hageman and Arrindell [Hageman, W.J.J.M ., & Arrindell, W.A. (1999), Establishing clinically significant change: in crement of precision and the distinction between individual and group level of analysis. Behaviour Research and Therapy, 37, 1169-1193], McGlinchey an d Jacobson [McGlinchey, J. B., & Jacobson, N. S. (1999). Clinically signifi cant but impractical? A response to Hageman and Arrindell. Behaviour Resear ch and Therapy., 37, 1211-1217.] reported practically identical findings on reliable and clinically significant change across the two approaches. This led McGlinchey and Jacobson to conclude that there is little practical gai n in utilizing the refined method over the traditional approach. Close insp ection of the data used by McGlinchey and Jacobson however revealed a serio us mistake with respect to the value of the standard error of measurement t hat was employed in their calculations. When the proper index value was uti lised, further re-analysis by the present authors disclosed clear differenc es (i.e. different classifications of S's) across the two approaches. Impor tantly, these differences followed exactly the same pattern as depicted in Table 2 in Hageman and Arrindell (1999). The theoretical advantages of the refined method, i.e. enhanced precision, appropriate distinction between an alysis at the individual and group levels, and maximal comparability of fin dings across studies, exceed those of the traditional method. Application o f the refined method may be carried out within approximately half an hour, which not only supports its practical manageability, but also challenges th e suggestion of McGlinchey and Jacobson (1999) that the relevant method wou ld be too complex (impractical) for the,average scientist. The reader is of fered the opportunity of obtaining an SPSS setup in the form of an ASCII te st file by means of which the relevant calculations can be carried out. The ways in which the valuable commentaries by Hsu [Hsu, L. M. (1999). A compa rison of three methods of identifying reliable and clinically significant c lient changes: commentary on Hageman and Arrindell. Behaviour Research and Therapy, 37, 1195-1202.] and Speer [Speer, D. C. (1999). What is the role o f two-wave designs in clinical research? Comment on Hageman and Arrindell. Behaviour Research and Therapy, 37, 1203-1210.) contribute to a better unde rstanding of the technical:statistical backgrounds of the traditional and r efined methods were also discussed. (C) 1999 Elsevier Science Ltd. All righ ts reserved.