Journal of Preventive Medicine and Public Health

The Korean Society for Preventive Medicine (대한예방의학회)
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Power Estimation and Follow-Up Period Evaluation in Korea Radiation Effect and Epidemiology Cohort Study

원전 코호트 연구의 적정 대상규모와 검정력 추정

  • Cho, In-Seong (Department of Preventive Medicine, College of Medicine, Seoul National University) ;
  • Song, Min-Kyo (Department of Preventive Medicine, College of Medicine, Seoul National University) ;
  • Choi, Yun-Hee (Medical Research Collaborating Center, Seoul National University Hospital/Seoul National University) ;
  • Li, Zhong-Min (Institute of Radiation Effect & Epidemiology, Seoul National University Medical Research Centre) ;
  • Ahn, Yoon-Ok (Department of Preventive Medicine, College of Medicine, Seoul National University)
  • 조인성 (서울대학교 의과대학 예방의학교실) ;
  • 송민교 (서울대학교 의과대학 예방의학교실) ;
  • 최윤희 (서울대학교 의학연구협력센터) ;
  • 이충민 (서울대학교 의학연구원 원자력영향역학연구소) ;
  • 안윤옥 (서울대학교 의과대학 예방의학교실)
  • Received : 2010.06.09
  • Accepted : 2010.10.12
  • Published : 2010.11.30
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Abstract

Objectives: The objective of this study was to calculate sample size and power in an ongoing cohort, Korea radiation effect and epidemiology cohort (KREEC). Method: Sample size calculation was performed using PASS 2002 based on Cox regression and Poisson regression models. Person-year was calculated by using data from '1993-1997 Total cancer incidence by sex and age, Seoul' and Korean statistical informative service. Results: With the assumption of relative risk=1.3, exposure:non-exposure=1:2 and power=0.8, sample size calculation was 405 events based on a Cox regression model. When the relative risk was assumed to be 1.5 then number of events was 170. Based on a Poisson regression model, relative risk=1.3, exposure:non-exposure=1:2 and power=0.8 rendered 385 events. Relative risk of 1.5 resulted in a total of 157 events. We calculated person-years (PY) with event numbers and cancer incidence rate in the nonexposure group. Based on a Cox regression model, with relative risk=1.3, exposure:non-exposure=1:2 and power=0.8, 136 245PY was needed to secure the power. In a Poisson regression model, with relative risk=1.3, exposure:non-exposure=1:2 and power=0.8, person-year needed was 129517PY. A total of 1939 cases were identified in KREEC until December 2007. Conclusions: A retrospective power calculation in an ongoing study might be biased by the data. Prospective power calculation should be carried out based on various assumptions prior to the study.

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