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. 2012 Jan 24;175(4):340–347. doi: 10.1093/aje/kwr317

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American Journal of Epidemiology Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health 2012.

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Figure 3. — The relative sample size necessary to achieve 90% power compared with the sample size necessary to achieve 90% power using the calibrated combination of 12 24-hour dietary recalls (24HRs) plus a food frequency questionnaire (FFQ), Eating at America’s Table Study, 1997–1998. The solid line shows results for calibrated 24HR(s) only. The dashed line shows results for a calibrated combination of 24HR(s) + FFQ. The dotted line shows results for the calibrated FFQ only. The vertical axis shows the relative sample size as a percentage; for example, a value of 200 means that the relative sample size is 200% of that required when using 12 24HRs plus an FFQ. A) Energy-adjusted total fat intake; B) energy-adjusted vitamin C intake; C) energy-adjusted intake of whole grains; D) energy-adjusted intake of dark green vegetables. See Web Appendix 7 for plots for the other dietary components.