The use of a single subject design to evaluate a potential adverse effect

The purpose of this paper is to illustrate the usefulness of a single subject design to examine a potential adverse reaction (weakness) to treatment (ultrasound) in a patient with tendonitis in their wrist. The patient received three pairs of true(u) and placebo (p) ultrasound treatments, the order of which were randomly assigned. Three grip strength measurements were taken before and after every treatment. The data were analyzed using inspection and a sign test based on the binomial distribution. Both analysis methods support the hypothesis that ultrasound did not cause an adverse reaction. Methodological issues are discussed as they apply to implementing N of 1 investigations.