A team of epidemiologists designs a prospective cohort study to investigate the relationship between high caffeine intake and the development of atrial fibrillation (AF). They enroll 2,000 participants who are free of AF at baseline and classify them into two groups based on self-reported daily caffeine consumption: high intake (≥5 cups of coffee per day) and low intake (<1 cup per day). Over a 5-year follow-up period, 180 of the 1,200 high-intake participants develop AF, whereas 80 of the 800 low-intake participants develop AF. Which of the following is the best estimate of the relative risk of developing atrial fibrillation associated with high caffeine intake compared to low caffeine intake in this study?