A prospective cohort study enrolled 200,000 adults without diabetes in 1990 and assessed their sugar-sweetened beverage (SSB) consumption at baseline. Participants were grouped by self-reported intake: none, 1–2 servings/week, 3–6 servings/week, and ≥1 serving/day. After 20 years of follow-up, investigators observed a graded increase in the relative risk of type 2 diabetes across the four consumption categories (relative risks: 1.0, 1.2, 1.5, and 2.0, respectively; p for trend <0.001). Concurrent animal and mechanistic studies demonstrated that high dietary fructose promotes hepatic de novo lipogenesis and insulin resistance. Which of the following Bradford Hill criteria is best demonstrated by the pattern of increasing relative risk with higher levels of SSB intake?