Power Estimation and Follow-Up Period Evaluation in Korea Radiation Effect and Epidemiology Cohort Study.
10.3961/jpmph.2010.43.6.543
- Author:
In Seong CHO
1
;
Minkyo SONG
;
Yunhee CHOI
;
Zhong Min LI
;
Yoon Ok AHN
Author Information
1. Department of Preventive Medicine, College of Medicine, Seoul National University, Korea. yoahn@snu.ac.kr
- Publication Type:Original Article ; English Abstract
- Keywords:
Cohort studies;
Epidemiologic studies;
Power;
Sample size;
Research design
- MeSH:
Adolescent;
Adult;
Aged;
Aged, 80 and over;
Child;
Child, Preschool;
Cohort Studies;
Dose-Response Relationship, Radiation;
Female;
Humans;
Incidence;
Infant;
Infant, Newborn;
Male;
Middle Aged;
Neoplasms, Radiation-Induced/*epidemiology;
Republic of Korea/epidemiology;
Risk;
Young Adult
- From:Journal of Preventive Medicine and Public Health
2010;43(6):543-548
- CountryRepublic of Korea
- Language:Korean
-
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 non-exposure 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.
