N-of-1methods in health behavior research: A systematic review

Introduction: 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
synthesized evidence about using N-of-1 methods to study and change
health behaviors, 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 behavior research.
Methods: Articles included were those which described observational or
interventional N-of-1 studies assessing health behavioral 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.
Results: 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 randomized 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). Only a small proportion (n=9) of the studies used
statistical techniques to analyze the data.
Conclusions: The systematic review highlighted a number of opportunities
and open questions for applying N-of-1 methods in future health
behavior research. There is scope for using N-of-1 methods in a wider
context to answer key questions in health behavior research.