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Table 1 Number of necessary events and sample size to obtain 80% statistical power

From: ROK study-C (Rainbow of KIBOU study-colorectum): a colorectal cancer survivor cohort study on food, nutrition, physical activity, psychosocial factors and its influences on colorectal cancer recurrence, survival and quality of life in Japan

Scenario Necessary number in two group
5-year Disease Free Survival
Unexposed group Exposed group Difference between exposed to unexposed Hazard Ratio of exposed to unexposed events sample size
90% 95% 5% 0.49 67 550
85% 80% 5% 0.65 173 862
80% 85% 5% 0.73 318 790
75% 80% 5% 0.78 491 1152
70% 75% 5% 0.81 684 1646
65% 70% 5% 0.83 884 1842
60% 65% 5% 0.84 1084 2002
  1. Necessary numbers are calculated with scenario where 7-year accrual and 5-year follow-up