The state of the art and future opportunities for using longitudinal n-of-1 methods in health behaviour research: a systematic literature overview

Abstract

n-of-1 studies test hypotheses within individuals based on repeated measurement of variables within the individual over time. Intra-individual effects may differ from those found in between-participant studies. Using examples from a systematic review of n-of-1 studies in health behaviour research, this article provides a state of the art overview of the use of n-of-1 methods, organised according to key methodological considerations related to n-of-1 design and analysis, and describes future challenges and opportunities. A comprehensive search strategy (PROSPERO:CRD42014007258) was used to identify articles published between 2000 and 2016, reporting observational or interventional n-of-1 studies with health behaviour outcomes. Thirty-nine articles were identified which reported on n-of-1 observational designs and a range of n-of-1 interventional designs, including AB, ABA, ABABA, alternating treatments, n-of-1 randomised controlled trial, multiple baseline and changing criterion designs. Behaviours measured included treatment adherence, physical activity, drug/alcohol use, sleep, smoking and eating behaviour. Descriptive, visual or statistical analyses were used. We identify scope and opportunities for using n-of-1 methods to answer key questions in health behaviour research. n-of-1 methods provide the tools needed to help advance theoretical knowledge and personalise/tailor health behaviour interventions to individuals.

Mindfulness for pain, depression, anxiety, and quality of life in people with spinal cord injury: a systematic review

“…Two studies failed to provide statistical results in support of their findings; only one study provided statistical measures of change, including p values, effect sizes, and 95% confidence intervals. Future work could consider using within-person units of analyses such as Ecological Momentary Analysis [31] or N-of-1 RCTs [32,33] for tailored interventions.…”

Challenges and proposed solutions for formative research to inform systematic intervention development in rare and unstudied conditions: The case example of Xeroderma Pigmentosum

“…Finally, N‐of‐1 or single‐case designs are recommended in rare diseases, as analysis is concerned with within‐participant temporal and contextual variation and power is derived from repeated observations rather than the number of participants (McDonald et al ., ). The lack of generalizability (particularly when bespoke protocols are used) that is sometimes a criticism of N‐of‐1 is also less relevant in rare diseases, where personalized/tailored interventions are used and there is considerable overlap in the formative and intervention samples.…”

Some t-tests for N-of-1 trials with serial correlation

“…first-order autocorrelation), and most studies fail to account for serial correlation. (McDonald et al, 2017;Smith, 2012;Gabler et al, 2011;Lillie et al, 2011). This work develops a formula-based statistical method for N-of-1 studies that accounts for serial correlation while using only the data from a single individual to draw inferences.…”