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Table 1 Computing annual intake of food items by multiplying average self-reported annual frequency of food intake by unit portion size

From: Association of self-reported consumption of cooked meat, fish, seafood and eggs with prostate cancer risk among Nigerians

Annual Intake Pattern Never Rarely Occasionally Sometimes Frequently Every Day
(Daily)
Many Times
(A Lot)
Reference 0/Year ≤6/Year 1–2/Month 1–2/Week 3–4/Week 5–7/Week ≥ 2/Day
Interval Boundary 0 365 × 2
Mid-Interval Value 0 3 18 78 182 312 730
Frequency
(3 Groups)
Rarely Sometimes Frequently
Annual Intake Mid-Interval Frequency × Unit Portion Size
Annual Intake
(4 Groups)
Transform to Quartiles