This design randomly assign twins within a pair, as a pair or randomly, matching for age, sex and genetic susceptibility

• Cross-over design for balance
• Under-used design to date

Examples

1. Response to exercise study
   (Green, Marsh et al., The University of Western Australia)
   a. Is response to exercise heritable?
   b. Does response to exercise depend on type of exercise?
2.  Back pain and insomnia study 
   (Ferreira et al., The University of Sydney)
   a. Does a specific web-based sleep intervention also improve back pain?
   b. Twins in each pair randomised to opposite arms (one to placebo, one to treatment)
   c. Primary outcome is activity limitation and functional outcome (measured by Patient-specific Functional Scale)
   d. The Actiwatch will be used to assess participants’ sleep disturbance

Analytic approach

• Extensions of previous methods
• Variance components modelling
• Linear and logistic regression with adjustment for correlation
• Systematic review of current approaches: 
  (Yelland et. al. 2015)
• Work in progress (Sumathipala et al. 2016)
• Power, sample size etc: Work in progress (Yelland et al. 2016)

Strengths

– Matching for genes could be critical
– Participation enhanced by pairing
– Motivated group

Limitations

Sharing – twins potential failure to adhere to protocol (including swapping devices).
– “Twins will be asked not to discuss with their co-twins about the intervention they are receiving.”

References

Yelland, L. N., Sullivan, T. R. and Makrides, M. (2015). Accounting For Multiple Births In Randomised Trials: A Systematic Review. Archives Of Disease In Childhood. Fetal And Neonatal Edition, (100) F116–F120.