Understanding Variation in Sets of N-of-1 Trials.

A recent paper in this journal by Chen and Chen has used computer simulations to examine a number of approaches to analysing sets of n-of-1 trials. We have examined such designs using a more theoretical approach based on considering the purpose of analysis and the structure as regards randomisation that the design uses. We show that different purposes require different analyses and that these in turn may produce quite different results. Our approach to incorporating the randomisation employed when the purpose is to test a null hypothesis of strict equality of the treatment makes use of Nelder's theory of general balance. However, where the purpose is to make inferences about the effects for individual patients, we show that a mixed model is needed. There are strong parallels to the difference between fixed and random effects meta-analyses and these are discussed

Self-reported smoking and alcohol use among adolescents with intellectual disabilities.

Self-reported smoking and alcohol use were examined among 95 adolescents (aged 11-15) with intellectual disabilities and 4069 adolescents who did not have intellectual disabilities. Results indicated that adolescents with intellectual disabilities reported increased rates of smoking and decreased rates of using alcohol at least once a month. There were no marked differences between the two groups on smoking seven or more cigarettes a day, having ever smoked at all and having ever used alcohol. Elevated levels of smoking appeared to be an artefact of increased rates of poverty among adolescents with intellectual disabilities. Distinct patterns of risk were associated with smoking and alcohol use among adolescents with intellectual disabilities. Smoking was closely associated with the experience of poverty and adolescent mental health. Alcohol use was associated with less punitive child management practices and carer mental health. Results are discussed in the context of health promotion