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. 2015 Oct 26;182(10):826–833. doi: 10.1093/aje/kwv225

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© The Author 2015. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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Figure 2. — Illustration of how the observation period of the dynamic (with respect to calendar time) hypothetical population in Figure 1 includes just some of the information from the corresponding fixed (with respect to start of exposure) cohort study in which follow-up would have started with first exposure or the corresponding date in the nonexposed. The time axis is exposure time and starts at initiation of exposure or beginning of follow-up in nonexposed persons (time 0). Solid horizontal lines (—) represent exposed time experienced by a person in a dynamic population; dashed horizontal lines (----) represent unexposed time; black squares (▪) represent incident cases; black circles (•) represent loss to follow-up.