Carryover Designs Including Washout Periods

• Activity Number: 255
• Type: Contributed
• Date/Time: Monday, August 10, 2015 : 2:00 PM to 3:50 PM
• Sponsor: Section on Physical and Engineering Sciences
• Author(s): Jonathan Stallings*
• Companies: North Carolina State University
• Keywords: Carryover design ; Washout period ; Optimal design

Abstract

Carryover designs (or repeated treatment designs) are frequently used when subjects are assigned multiple treatments across sequential periods. Different treatments are often applied with little time between them, potentially leading to residual treatment effects in subsequent periods. One way to eliminate the residual effect is to include a washout period, during which no treatment is assigned to the subject. However, this increases the overall time required for the experiment to be conducted. Because of this, washout periods are not included, and optimal carryover designs are constructed based on a statistical model incorporating the residual effects. In this talk, I consider repeated treatment design scenarios in which some, but not all, treatments may be followed by a washout period. I detail the necessary modifications to the usual carryover model and highlight their impacts on optimal designs for estimation of direct and residual treatment effects. Optimal designs are then derived for specific cases of the number of subjects, periods, and treatments.