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Precise metnodologyconveys the value andvalidity of dietary data

ietary data are an essential outcomemeasure in many clinical andepidemiologic studies. The increas-

ing emphasis on research aimed at clarify-ing the links among diet, health, and dis-ease heightens the need for carefully col-lected data on food and nutrient intake.

Surprisingly, many reports in the nutri-tion and medical literature devote littleattention to explanation of the proceduresused to collect and analyze dietary data. Itis not uncommon to find dietary assess-ment methodology dispatched in one ortwo sentences, such as the following ex-amples: "Trained interviewers obtained so-cioeconomic and food habit informationfrom the subjects in their homes using anoral questionnaire. A 24-hour diet recallwas also taken." "The women's dietarycalcium and vitamin D intakes were esti-mated every 6 months using a food fre-quency questionnaire." "Subjects kept 3-day dietary diaries each month for aminimum of 12 months. They reported tothe department on a monthly basis to re-view and clarify diary entries."

A guiding principle for reporting re-search is that methodology should be de-scribed in sufficient detail to enable an-other researcher to duplicate the studydesign. Description of dietary assessmentmethodology should be just as precise asthat for otherresearch procedures, such aslaboratory tests.

Why do many researcher-authors fail toreport dietary assessment methodologywith clarity and precision? There are sev-eral possible explanations:* Investigators may not have included adietetics professional onthe research teamwhenplanning the studyand, consequently,may not realize the importance of definingthis type of methodology.

Madelyn L. Wheeler, MS, RD, iscoordinatorfor research dietetics atthe Diabetes Research and TrainingCenter at Indiana University MedicalCenter, Indianapolis. I. MarilynBuzzard, PhD, RD, is director of theNutrition Coordinating Center,Division of Epidemiology, School ofPublic Health, at the University ofMinnesota, Minneapolis.

Correspondence regarding thisarticle should be directed to M. L.Wheeler at the Diabetes Research andTraining Center, Regenstrief HealthCenter, Room 234, 1001 W 10th St,Indianapolis, IN46202.

asssment dataCheckist for rpeorting dietary ntake methodology

Guidelines for all assessment methodsv Describe the time frame of interest. Examples include:

* Usual intake over the past year, including any seasonal variations.* Defined period preceding disease incidence.* Current intake (eg, during the past week or month).

V Provide rationale for selecting the method used to collectdietary data.* If an existing method was used, cite published articles that describethe method and document its validity and reliability.* If an existing method was modified, describe key points of the originalmethod and all modifications. Cite references to the original method,including validation and reliability studies.* If a new method was developed, describe the procedures used todevelop and evaluate the new tool.

V Describe the results of pretests of the selected assessment methodconducted with either the target subjects or a similar population.

V Describe procedures used to quantify portion sizes of foods eaten.* State the use of food scales, household measuring cups or spoons,rulers, food pictures, food models, or geometric shapes.

v Describe procedures used to analyze dietary data. If nutrientswere calculated,* Identify the food composition database used by name, version number,and release date and provide the name and location (city and state) of thedatabase developer.* Evaluate the completeness of the database for the nutrients of interest.* Describe any modifications to the database.* Describe procedures for coding the data.* Describe quality-control procedures for ensuring accurate calculations.

V Indicate whether the assessment tool was administered by aninterviewer or self-administered by respondents.

When interviewer-administered methods are used:* Describe the minimum qualifications of interviewers (eg, registereddietitian status, graduate degree in health science field).* Describe training and certification procedures for interviewers.* Indicate whether interviews were conducted in person or by telephone.* Report the approximate length of the interview.* Describe the level of detail solicited about food descriptions (eg, type orbrand of food; processing method, such as canned or dried; eatingpractices, such as trimming of meat or use of table salt; specification ofrecipe ingredients and other food preparation methods).* Indicate whether the method used to query respondents for details aboutfood intake was automated (interactive computer software that prompts fordescriptive detail) or manual; describe any aids used for manual probing,such as a checklist of details required for each food category.

When self-administered methods are used:* Describe instructions or training provided to subjects on keeping foodrecords or completing dietary questionnaires.* Describe materials provided to help subjects describe foods (eg,checklist of details required for each food category) or estimate portionsizes (eg, food scales, household measures, or food models).* Describe procedures used to collect additional information after the foodrecords or questionnaires are completed.

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Checkidst for reporting dietary intake methodologyAdditional sidelines for specific assessment methods

v Food records and 24-hour recalls* Designate the number of days recorded, which days, and whether dayswere consecutive; describe any weighting algorithms used to account forday-of-the-week differences.

v Food frequency methods (list-based diet histories)* Explain the purpose of the questionnaire (eg, to rank individualsaccording to their intake of individual foods, food groups, or nutrients)and identify the nutrients of interest.* Identify the population group (eg, ethnicity and age range) used todevelop and validate the questionnaire.* Explain how the food list was developed.* Indicate the number of foods and food groups in the food list.* Indicate the level to which food consumption was quantified.'If relevant, comment on respondents' ability to designate small, medium,or large servings.* Describe the options available for specifying frequency of consumption.* Indicate the average length of time required to complete thequestionnaire.* Describe any calibration studies designed to facilitate interpretation ofthe food frequency data.

V Diet history methods (meal-based diet histories)* Indicate whether questions were open-ended or structured.* Indicate the number of "typical" days accounted for as well as theextent of probing for variations in the usual eating pattern.* Describe methods used to cross-check the history, such as a 24-hourrecall or food frequency checklist.

I Food frequency questionnaires can be unquantified, semiquantified, orcompletely quantified. An unquantified method does not specify servingsizes; instead, the respondent indicates how many times the food isconsumed per period of time (day, week, month). For example, a respon-dent may be asked, "How often do you consume milk?". A semiquantifiedmethod provides typical serving sizes as the reference amount fordetermining frequency of consumption. For example, "How often do youconsume an 8-oz glass of milk?". A completely quantified method allowsthe respondent to indicate any amount of food typically consumed as wellas how often the food is consumed; amounts are obtained through open-ended questions, usually prompted by an interviewer. For example,"When you drink milk, how much do you usually consume?".

Resources for develng, using, and reportingdintesan mgaeme m maent lnmnsaUrUmU' UIWWwwguiNL INUwgMUlluuJ

* Investigators may mistakenly think pro-cedures for assessing dietary intake are"standard" and that it is unnecessary toreport them in detail because readers "willknow" how to reproduce the procedures.* Some journal editors and reviewers failto enforce standards for scientific publica-tions. If a researcher-author omits appro-priate methodology in a submitted manu-script, it is the responsibility of the editorand/or peer reviewers to ask the author toprovide clarification.* There is little or no guidance - and cer-tainly no gold standard - to help authorsdecide what to report as methodology.

Consequently, we've devised two check-lists that offer guidance concerning thetype and detail of information researchersshould include in the methods section ofpapers reporting dietary assessment data.The first checklist (see box on page 1255)presents general guidelines for reportingdietary assessment methodology thatshould be applied to all research reports,regardless of the method of dietary assess-ment used. The second checklist (see boxat left) outlines additional specific sugges-tions for reporting about three categoriesof dietary assessment tools: food recordsand recalls, food frequency questionnaires,and diet histories.

Until more formal guidelines are sanc-tioned by an official body of nutrition sci-entists, we hope these checklists provideresearchers a structure for ensuring con-sistency and clarity when reporting di-etary data. We encourage editors of nutri-tion-related journals to incorporate theseor similar guidelines into their "guidelinesfor authors."

I. Marilyn Buzzard is a member of theorganizing committee for the SecondInternational Conference on DietaryAssessment Methods, which will beheld January 22-24, 1995, in Boston,Mass. Discussion topics include newdevelopments in dietary assessment,errors in interpreting data, andapplications for diverse cultures. Forregistration information, see Educa-tional Events on page 1251.

Lee RD and Nieman DC. NutritionalAssessment. Dubuque, Iowa: William C.Brown Publishers; 1993: chapters 1-3.

Buzzard IM and Willett WC, eds. Dietaryassessment methods. The AmericanJournal of Clinical Nutrition. 1994;59(supplement): 143S-306S.

Cameron ME and Van Staveren WA.Manual on Methodologyfor FoodConsumption Studies. New York, NY:Oxford University Press; 1988.

Gibson RS. Principles of NutritionalAssessment. New York, NY: OxfordUniversity Press; 1990: chapters 3-4.

Hankin JH. Dietary intake methodology.In: Monsen ER, ed. Research: Success-ful Approaches. Chicago, ll: AmericanDietetic Association; 1992: 173-194.

Pennington JAT. Development and use offood composition data and databases.In: Monsen ER, ed. Research: Success-ful Approaches. Chicago, l: AmericanDietetic Association; 1992: 195-203.

Willett W. Nutritional Epidemiology.New York, NY: Oxford University Press;1990: chapters 4-7.

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