New Single-Subject and Small-n Design in Occupational Therapy: Application to Weight Loss in Obesity Deborah Weissman-Miller, Mary P. Shotwell, Rosalie J. Miller KEY WORDS  biostatistics  models, statistical  obesity  outcome assessment (health care)  research design Deborah Weissman-Miller, ScD, MS, MPH, PdCE, MEOE, is Affiliate Professor of Biostatistics, School of Occupational Therapy, Brenau University, 500 Washington Street SE, Gainesville, GA 30501; dweissman-miller@ brenau.edu Mary P. Shotwell, PhD, OT/L, is Associate Professor and Director, Weekend Program, School of Occupational Therapy, Brenau University, Gainesville, GA. Rosalie J. Miller, PhD, OTR, FAOTA, is Professor and Director of Doctoral Programs, School of Occupational Therapy, Brenau University, Gainesville, GA. Ottenbacher (1986) showed the usefulness of single-subject design (SSD) in occupational therapy. However, SSD methodology is not regarded by the wider research community as providing statistically reliable and valid evidence of effectiveness of treatment partly because of its observational nature. Although statistical estimations can also be made from least squares regression or by a trend line, a new methodology has great potential to influence research in occupational therapy. The new model enables the use of initial client data from the beginning of treatment (for single subjects or small groups) to determine a point in the linear regression at which predictions can be made for the number of treatments needed for stability or improve- ment. This model is invaluable for third-party payment as well as for client motivation. The purpose of this article is to present this new methodology, the semiparametric ratio estimator (SPRE), illustrated by case application to treatment of obesity. Weissman-Miller, D., Shotwell, M. P., & Miller, R. J. (2012). New single-subject and small-n design in occupational therapy: Application to weight loss in obesity. American Journal of Occupational Therapy, 66, 455–462. http://dx. doi.org/10.5014/ajot.2012.004788 O ur objective in this article is to present a new statistical method that addresses the needs of and problems in quantitative research identified in occupational therapy over the past 30 yr (Banigan et al., 2008; Davies & Case-Smith, 1998; Ellenberg, 1996; Ottenbacher & York, 1984; Rogers, 2010). Ottenbacher’s (1986) work exposed occupational therapy to single- subject design (SSD). Although this methodology helped the profession with research involving small numbers of participants, SSD is observational in nature and unable to predict future outcomes, nor is it able to indicate the number of treatment sessions in which the client demonstrates a change and at what point in treatment the client will stabilize his or her performance. In this article, we present a new methodology, a semiparametric ratio es- timator (SPRE), with a case application to the obesity population. This new model, used in primary or secondary analysis of the outcomes of the participant during treatment or for the predicted response to treatment, addresses the stated goal of the Centennial Vision for the profession of occupational therapy to be science driven and evidence based (American Occupational Therapy Associa- tion [AOTA], 2005). The challenges to attaining this goal are many. Not only are “the inherent difficulties associated with describing and investigating true outcomes of intervention complicated by the nature of occupational therapy—the use of occupation as therapy” (Robertson & Colborn, 2000, p. 541), but also, “when using the classical sums-of-squares linear approach to statistics, the contribution of one variable is examined at one time, independent of the contribution of other variables” (Davies & Case-Smith, 1998, p. 524) in which the ordinary least squares approach constitutes the total analysis and in which this analysis does not coincide with occupational therapy’s holistic approach. The challenge The American Journal of Occupational Therapy 455 Downloaded From: http://ajot.aota.org/ on 10/24/2018 Terms of Use: http://AOTA.org/terms