Frequently Asked Questions
Calculating HEI Scores
Scoring a set of foods requires that the foods be mapped to food groups and certain nutrients (such as sodium and fatty acids). NCI-developed tools accomplish this using the Food and Nutrient Database for Dietary Studies (FNDDS) and the Food Patterns Equivalents Database (FPED). These databases provide nutrient amounts in foods (FNDDS) as well as disaggregate foods as eaten into the food group components (FPED) that are used in calculating HEI component scores. Examples of diet assessment tools NCI has created include the Automated Self-Administered 24-hour Dietary Assessment Tool (ASA-24, collect 24-hour recalls or food records) and the Diet History Questionnaire (DHQ, a food frequency questionnaire).
A set of foods can theoretically be mapped to the FNDDS and FPED by hand, for example if you have collected information about a person’s diet using a food frequency questionnaire whose output is not automatically linked to the food codes in FNDDS and FPED. Another option is to analyze the set of foods you are studying (i.e. a person’s diet; a cafeteria menu; a grocery store flyer; etc.) with a program that is linked to these or other similar databases already, such as ASA24, the DHQ or data collected with the fee-based Nutrition Data System for Research (NDSR).
How do I know which method to use to calculate the HEI score of my data?
There are a variety of methods you can use to calculate an HEI score depending on the research question you are trying to answer and the data you have. See Overview of the Methods and Calculations to find more information about the methods that can be used to calculate HEI scores based on the research question you are trying to answer.
How do the methods proposed for analysis of the HEI adjust for measurement error?
The recommended approaches for estimating means and distributions of scores for a population, subpopulation, or group are intended to minimize the effects of measurement error in dietary intake data such that the results better reflect HEI scores for usual intake. There are two primary sources of measurement error, random and systematic errors. The only way to mitigate systematic errors is by using an unbiased method (such as a recovery biomarker), or a less biased method (such as a 24HR) to calibrate the dietary assessment measurement. When more than one dietary assessment is available on an individual, statistical methods may be used to adjust for random error.
The methods proposed for analysis of usual intake based on 2 days of intake only adjust for random error. Little is known about the impact of systematic error on the results of analyses that make use of the HEI. Biomarker-based validation studies focusing on energy and protein have shown that the observed effects of diet on health are biased (typically toward the null, or attenuated) when diet is measured with error. Energy adjustment appears to lessen, though not eliminate, this problem. The extent to which these findings apply to models using the HEI is not yet fully understood. Until more is known about the effects of measurement error on analyses using HEI total or component scores as exposures in regression models, researchers should consider the potential for bias due to error in the interpretation of their results.
Is there an HEI tool or instrument needed to calculate an HEI score?
The Healthy Eating Index is a standardized scoring metric that can be used to score any set of foods to evaluate quality as compared to the Dietary Guidelines for Americans. There is no tool or questionnaire specific to the HEI because it can be used to score any set of foods, such as a population’s diet, a shopping basket, a menu, or an individual’s dietary intake.
To score dietary intakes, a researcher or clinician should use a food record or ideally at least several 24-hour recalls, or a food frequency questionnaire to determine the variables needed to calculate the HEI. The NCI has developed versions of these tools that could be used to get the food group output needed to calculate the HEI, including the Automated Self-Administered 24-hour Dietary Assessment Tool (ASA-24, collect 24-hour recalls or food records) and the Diet History Questionnaire (DHQ, a food frequency questionnaire, new version coming soon). Researchers and clinicians might find it helpful to become familiar with the pros and cons of these tools depending on their research question and study or patient population. More information on this can be found in the Diet Assessment Primer.
Can I calculate HEI scores using Nutrition Data System for Research (NDSR) or Automated Self-Administered 24-Hour Recall System (ASA24)?
SAS code that can be applied to FFQ data to estimate total and component scores for each individual is currently available on the SAS Code page.
This code uses NIH-AARP Diet and Health Study data as an example. This code estimates component and total HEI scores for each individual and can be modified for use with other FFQs.
Where do I find the SAS code to calculate the HEI score?
See SAS Code for links to code that will help calculate HEI scores and perform other tasks such as calculate distributions of scores of estimated usual intake.
Can I use other statistical software packages besides SAS to calculate the HEI score?
Yes, it is possible to use other software packages to calculate HEI scores. Programming in other software packages must be done on your own. Sample code is provided in SAS only.
Citing HEI in Research Papers
Though citation format will vary depending on the journal style you are following, the general information that should be included in the citation of the HEI website includes the author (National Cancer Institute), the web page title (such as The Healthy Eating Index - Population Ratio Method) and the URL where the information is located. For example:
National Cancer Institute. The Healthy Eating Index – Population Ratio Method. https://epi.grants.cancer.gov/hei/population-ratio-method.html. Updated August 29, 2017. Accessed (insert date).