We calculated cumulatively updated caffeine intake by averaging the
intake from all available dietary assessments up to the start of each 2-
year period at risk. As glaucoma is a slowly developing chronic
condition, we chose to study cumulatively averaged caffeine intakes as
they best represented long-term intake, and average measures have less
measurement error than single assessments.45 All caffeine intakes at
each questionnaire were adjusted for total energy intake by using the
residual method.