Key Concepts about Measurement Error

Note: Because Measurement Error and Validation are closely related concepts in dietary assessment using self-report instruments and are equally important to being able to conduct research using these instruments, we suggest that you read both Key Concepts sections of the Primer in tandem. You may also wish to work with a statistician in applying the concepts described here.

Because dietary intake can rarely be directly observed, we typically rely on self-report instruments, such as 24-hour dietary recalls (24HR), food records, food frequency questionnaires (FFQ), screeners (see Instrument Profiles), and diet history instruments (Learn More about Diet History). Choosing a self-report dietary assessment instrument involves many considerations about the types and extent of measurement error that characterize data collected using these different instruments.

Measurement error refers to the difference between the value obtained from a measure and the true value of a parameter. For dietary data, measurement error refers to the difference between reported dietary intake over a specified time period and true [glossary term:] usual dietary intake. This problem affects all kinds of data in addition to dietary intake data, such as measures of weight, height, or blood pressure that are self-reported or taken with poorly calibrated equipment. Although data collected from some dietary assessment instruments are known to be more prone to error than others, researchers may choose to use a particular instrument in a given study for practical reasons, such as cost. However, if the error is ignored, the results may be misleading.

In dietary assessment, we are often interested in assessing usual dietary intake (i.e., long-term average) rather than intake on a given day or other short-term time period (i.e., acute intake). Measurement error poses a particular challenge to estimating usual intake using self-report instruments.

This section of the Primer provides a brief background on measurement error in dietary intake data and its effects on study results. Other sections of the Primer provide more specific information: