The minimum detectable HR for the analysis of the relationship between incident CHD and nutrient density quartiles of choline, betaine, and choline + betaine were estimated for the WHI OS cohort. We conservatively evaluated study power by calculating the effect size that could be detected using the number of WHI OS events as of September 12, 2005, 7.58 mean years of follow-up, accrual period of 4.33 years, with an α = 0.05 and power set at 80% and 90% (Table III.7).45-47 For the purposes of these calculations we assumed that the choline and betaine exposures are grouped in quartiles. Quartile 4 was considered the referent group and we assumed that it had the same event rate as the entire WHI OS cohort. nQuery advisor 5.0 software (Statistical Solutions, Saugus, MA) was used as the
computational tool. The values in Table III.7represent the minimum detectable HR’s and corresponding power for any given comparison between Quartile 4 and each of the other quartiles.
Table III.7 Minimum detectable hazard ratios given 80% and 90% power and α = 0.05, when examining the hazard of cancer outcomes by energy-adjusted quartiles of choline, betaine, and choline + betaine, in the WHI observational study.
Disease endpoint Number of events (%) Minimum detectable hazard ratio Power
Coronary Heart Disease 2,471 (2.64 ) 1.16 0.80
1.19 0.90
Clinical Myocardial Infarction 1,898 (2.02) 1.19 0.80
1.22 0.90
CHD Death 824 (0.88) 1.30 0.80
1.35 0.90
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CHAPTER IV
RESULTS
IV.1 Estimation of the dietary intakes of choline and betaine intake in the Women’s