A prospective cohort study was conducted to investigate a possible relationship between Diet and Attention-Deficit Hyperactivity Disorder (ADHD) in children.After assessing dietary habits of a sample of young pre-school children (who were all free of ADHD at baseline) they were categorised as either 'Healthy eaters' or 'Unhealthy eaters' and were followed up for the next three years. At the end of the follow-up period, there were a total of 6275 children in the Unhealthy eaters group (exposed) and 674 had developed ADHD while there were a total of 10986 children in the Healthy eaters group and 199 cases of ADHD were recorded. Calculate a suitable measure of association to explore if there is a link between poor diet and ADHD. Please provide only the final answer with two decimals and use of brackets is essential.