A researcher wants to measure the long-term intake of lycopene, a dietary antioxidant, and determine whether it is associated with decreased risk of heart disease. Three methods are available but vary in cost, accuracy and easy of application.

- Food-frequency questionnaire (FFQ or simply Q): This method is cheaper and easier to administer and is the most used method in nutritional epidemiological studies

- Dietary recalls/records (R): May be more accurate than the FFQ but could be more expensive and require repeated measurements. These measurements could be correlated.

- Biomarker (M): Here lycopene concentrations in plasma are measured. The method may be more accurate but is rather expensive and involving.

Because of the cost and time, two methods R and M are applied only on a sub-sample (e.g. 10-20%) of the study subjects. The next slide shows data from a design with three methods for measuring the exposure.