Why is it important to assess dietary measurement error?

Nutritionists routinely conduct research and monitoring activities that depend on self-reported dietary intake information from questionnaires and interviews. Dietary recommendations aimed at encouraging people to follow dietary patterns to promote health and reduce disease risks are also based in part on information gathered through these means. Food frequency questionnaires, which measure a person's usual intake over a defined period of time, and 24-hour recalls, in which a person records everything eaten or drunk during the previous 24 hours, are among the methods of choice for collecting information about what people are consuming.

The problem is that people don't always report accurately. In addition, these commonly used dietary assessment instruments are subject to substantial error, both random and systematic. Interpreting findings from epidemiology and monitoring research is critically dependent on understanding the nature and extent of the measurement error contained in these instruments.