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Dice displaying randomisation

At the beginning of the study, whether each participant received aspirin or placebo (dummy) tablets was determined randomly (like tossing a coin). Each participant had a 50% chance of receiving aspirin and a 50% chance of receiving the placebo tablets. The brown capsules each contain 1 gram of naturally occurring oil either mainly omega-3 fatty acids or mainly olive oil. Each participant had a 50% chance of receiving the omega-3 fatty acids.

ASCEND is a ‘double blind’ study which means that neither the study participants nor the doctors looking after them know which treatment an individual is taking. This design helps to ensure that the results of the study are reliable. However, if it was ever medically necessary, information about which treatment a participant is taking can be given to the participant's doctors by staff at the coordinating centre.

At the end of the study what happened to the participants who were allocated to receive active aspirin will be compared with what happened to those who were allocated to receive placebo. In particular, the number of people in each group who suffered a heart attack or a stroke and the number of people who developed a serious bleeding problem will be compared. Any difference between the groups is likely to be due to the effect of the aspirin treatment. Similarly, what happened to those allocated to receive the omega-3 fatty acids will be compared to what happened to those allocated to receive the olive oil.