Waist and hip circumference

Subjectively assessed waist and hip circumferences are often used in large-scale epidemiological studies to describe body fat distribution when the objective measurements are not feasible.

Individuals self-report their waist and hip circumferences or it is reported on their behalf by a proxy-reporter. Examples of frequently used questions:

• "What is your waist size?"
• "What is your hip size?"

Instructions

Accuracy of the subjective waits and hip circumferences may be higher if participants are provided with clear instructions and a standard tape measure; otherwise participants may report circumferences based on their clothing sizes, which is less accurate. Detailed instructions such as taking the measurement after breathing out normally, with the stomach relaxed and not pulled in may also contribute to greater accuracy.

Selection of data source

Data can be collected by interview, by self-administered questionnaire, or be collected by proxy reporter (e.g. friend or family member). Questions can be administered using pen and paper or an electronic device such as a mobile phone, tablet or computer, either face-to-face or remotely (e.g. by post or internet).

Validation study

When studies rely on subjective methods, a validation study in a sub-sample of the main study cohort may provide useful information to quantify the errors/bias; corrections can then be carried out at the analysis stage (see below).

If collecting repeated subjective data at different time points, their validity should ideally be monitored as this may vary over time.

Units of measurement

Unit of the measurement (e.g. metric units or imperial scale) should be clearly defined to avoid discrepancy in recorded height. Incorrect conversion may lead to substantial errors. Units should be appropriate for the population of interest, possibly providing a choice of alternatives.

Waist and hip circumferences, and calculated waist to hip ratio (waist divided by hip) are often used in epidemiological studies as estimates of central and peripheral fat and relative fat distribution.

It is possible to apply statistical methods that correct for or take into account errors if relevant validation data are available. Predictive equations for objectively measured circumferences using data from a random sample of the main cohort can be derived and applied to the whole cohor. For height and weight there are available prediction equations, but these are not widely available for waist and hip.

An overview of subjective waist and hip circumference methods is outlined in Table A.2.10.

Strengths

• Low cost
• Practical tool as it can be included in study questionnaires and be self-administered
• Information can be obtained via mail, face to face or telephone interviews or the Internet
• Can be obtained retrospectively
• Low respondent burden
• Large number of individuals can be approached
• Non-intrusive
• It could increase recruitment rates and participation retention, especially by individuals who are reluctant to be measured
• No fieldwork required if self-administered or data collected online

Limitations

• Prone to systematic errors in reporting by different body size and social-demographic characteristics
• Prone to response bias e.g. social desirability
• May not be feasible in certain population where recall bias is high (e.g. mis-reporting of this measure is higher in older individuals when compared to younger individuals).
• Corrections may be necessary at analysis point

Characteristic	Comment
Number of participants	High
Relative cost	Low
Participant burden	Low
Researcher burden of data collection	Low
Researcher burden of coding and data analysis	Low
Risk of reactivity bias	No
Risk of recall bias	Yes
Risk of social desirability bias	Yes
Risk of observer bias	Yes
Space required	Low
Availability	High
Suitability for field use	High
Participant literacy required	Yes, if self-administered
Cognitively demanding	Yes

The accuracy of circumference measures varies with body size, age, sex, education and socio-economic status. ‘Figure consciousness’ also appears to affect the reporting of these data, especially in men. Considerations relating to the use of waist and hip methods in specific populations are described in Table A.2.11.

Population	Comment
Pregnancy
Infancy and lactation
Toddlers and young children
Adolescents	Younger people tend to more frequently underreport their waist and hip circumferences compared to older groups.
Adults	Men tend underreport waist circumference more frequently than women.
Older Adults
Ethnic groups
Other	Overweight individuals tend to underreport waist and hip circumferences more frequently compared to leaner people. Underestimation of waist circumference is also more frequent among participants with lower educational level and social class.

• Minimal resources are generally required with subjective methods as field work may not be necessary
• Tape measure
• Questionnaire via paper and pen or electronic device
• Instructions for completion and return regardless of media
• For mailed questionnaires a pre-paid stamped address envelope
• Trained interviewers for interviewer-administered tools, plus standard operating procedures for interviewers
• Data entry cleaning code
• Standard operating procedures for data entry errors/extreme values/data cleaning
• Statistical knowledge may be required if correction factors are applied to the data

A method specific instrument library is being developed for this section. In the meantime, please refer to the overall instrument library page by clicking here to open in a new page.