N-of-1 methods in health behaviour research: a systematic review

Abstract

Background: Conclusions from between-participant studies often misrepresent variability between individuals and variability within individuals over time. N-of-1 methods involve the repeated measurement of an individual over time to make conclusions about that individual. This study synthesised evidence about using N-of-1 methods to study and change health behaviours, using examples from a systematic review of the literature, with the aim to describe the state of the art, unmet challenges and future opportunities for health behaviour research. Methods: Articles included were those describing observational or interventional N-of-1 studies assessing health behavioural outcomes in any population and reported data analysis and conclusions at the individual level. A comprehensive search strategy was used to search databases for articles published 2000-2013 meeting inclusion criteria. Findings: 3973 potentially relevant records were identified of which 31 full-text articles met inclusion criteria. The included studies used observational designs (n=2) and interventional designs including AB (n=14), ABAB (n=1), alternating treatments (n=3), N-of-1 randomised controlled trial (n=3), multiple baseline (n=7) and changing-criterion (n=1) designs. Studies assessed medication/treatment adherence (n=14), physical activity (n=11), recreational drug use (n=3), sleep (n=2), alcohol use (n=2), and smoking (n=1). In most of the studies, the data were evaluated using visual analysis (n=24) and some used statistical techniques (n=7), Conclusions: The systematic review highlighted a number of opportunities and open questions for applying N-of-1 methods in future health behaviour research. There is scope for using N-of-1 methods in a wider context to answer key questions in health behaviour research.