Importance of adequate sample sizes in fatty acid intervention trials

Randomised controlled trials are the ideal way to assess the effects of interventions. Small trials are useful for generating pilot data to determine samples sizes for larger trials, but can produce unreliable or biased results if they are considered in their own right. We investigate the impact of small sample sizes due to either inadequate recruitment targets or high attrition rates on the results of fatty acid intervention trials. Data from our large trial of DHA supplementation during pregnancy with minimal attrition are used for illustration. Our findings demonstrate that recruiting fewer participants or neglecting to follow up difficult participants can lead to substantially different results and alter conclusions about the effectiveness of the intervention. Developing strategies for overcoming these inadequacies should be a top priority in fatty acid intervention trials.