To evaluate the mechanisms by which borage seed oil and echium seed oil block mediator generation in asthma, we performed a cross-over trial design to reduce the numbers of patients needed for the study. Each treatment period was six weeks with a six-week washout period. For simplicity all power calculations are made assuming a single factor or predictor variable and a single result or outcome variable. We focused on changes in mediator generation by effector cells. Calculations below suggest that we have resolution to pick up clinically meaningful effects of potentially important explanatory variables with acceptable or high power.