Quantification of Self-Reported Caffeine Use - Caffeine: Chemistry, Analysis, Function and Effects - page 231

This chapter will discuss the utility of self-reported caffeine use as well as
other methods used to measure caffeine use. Issues involving the use of
standardized caffeine content information and the validation of self-reports
with physiological caffeine concentrations will also be addressed.

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13.2 Estimation of Dietary Caffeine Consumption
The long-term effects of habitual caffeine use on health and behavior are
commonly studied by identifying and comparing naturally low caffeine
consumers with naturally high caffeine consumers. The most economical and
efficient characterization of normal caffeine use consists of an individual's self-
reported behavior. Self-reports of caffeine intake may be either retrospective or
prospective questionnaires or interviews. Self-reported drug use is sometimes
suspected of being unreliable, since individuals may have reason to be
deceptive about illicit drug use. However, self-reports of illicit drugs have been
shown to be valid and reliable, and since caffeine use is an accepted part of
Western culture, self-reports are not likely to be biased by social desirability
concerns.
Caffeine use estimates are most accurate when they are adjusted for the
approximate caffeine concentrations for each type of food, beverage, or
medication, as well as the amount and frequency of use. Therefore, a thorough
caffeine use questionnaire or interview should query each source of caffeine
(e.g., coffee, chocolate, tea, soft drinks, energy drinks, medications, supple-
ments, etc.), the brand names, the number of occasions each source is
consumed per day, number of beverages or amount ingested per occasion, the
volume per beverage, the brewing method (e.g., drip-brewed, French press,
instant, espresso), the brewing duration, whether the chocolate was milk or
dark, whether the coffee and tea was regular or decaf, and whether the tea was
green or black and iced or hot. Dilution with milk or ice should also be noted
and factored into the volume calculation. Previously we have used a caffeine
consumption questionnaire (CCQ) described in Landrum (1992) and modified
to include other sources of caffeine such as energy drinks and medications, see
Table 13.1 for an example. The CCQ is divided into four columns for different
time periods (e.g., morning, afternoon, evening) with separate rows for each
type of caffeinated food, beverage, and medication, as well as the brewing
method for coffee. This was used both as a retrospective interview guide and as
a prospective diary (Addicott et al 2009).

13.2.1 Self-report Methods
Retrospective self-reports of caffeine use are usually questionnaires or
interviews of past or typical caffeine use. The retrospective report is more
time-efficient than the prospective method and is more commonly used. In
addition, a skilled interviewer may be capable of soliciting a more thorough
and systematic history than a paper-and-pencil questionnaire. Most impor-