Diet History Questionnaire: Frequently Asked Questions

General

Administering the Questionnaire

Validation

Scanning Equipment

Nutrient Estimates

Calculations

Modifying the DHQ

Data Quality Issues

HHHQ and DietSys


General

Must the DHQ be scanned to be usable? Can't I just key the data into a file myself?

Diet*Calc requires an ASCII text file containing the DHQ data. If using paper questionnaire forms, it is recommended that you create the data file by scanning the forms. However, the questionnaire data file can be created using any data entry system available to you. Information that we receive regarding specific data entry systems being used to enter DHQ data will be posted as it becomes available.


Is there a suggested citation for Diet*Calc and the DHQ?

Citations for Diet*Calc, the DHQ, and the nutrient database, indicating the version, are recommended. See Suggested Citations for examples.


What costs are associated with the DHQ and Diet*Calc?

The Diet*Calc software is free, but there may be costs associated with printing the DHQ and scanning or entering the data. View the DHQ Forms section for options for obtaining the forms and capturing the data. If you make many changes to the questionnaire, this requires some sophistication with respect to modifying the Diet*Calc software so that the modified questionnaire is properly analyzed -- a good computer savvy person would be helpful.

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Administering the Questionnaire

How long does the questionnaire take to complete?

Based on pilot study research from about 400 individuals, the questionnaire takes about 1 hour to complete.

Subar AF, Ziegler RG, Thompson FE, Johnson CC, Weissfeld JL, Reding D, Kavounis KH, Hayes RB for the Prostate, Lung, Colorectal, and Ovarian Cancer Screen Trial Investigators. Is shorter always better? Relative importance of questionnaire length and cognitive ease on response rates and data quality for two dietary questionnairesExternal Web Site Policy. Am J Epidemiol 2001;153(4):404-9.

Subar AF, Thompson FE, Kipnis V, Midthune D, Hurwitz P, McNutt S, McIntosh A, Rosenfeld S. Comparative Validation of the Block, Willett, and National Cancer Institute Food Frequency Questionnaires: The Eating at America's Table StudyExternal Web Site Policy. Am J Epidemiol 2001;154:1089-99.


What information do you have on response rates for the DHQ?

Based on pilot study research from about 400 individuals in one study and about 1000 in another, the response rates for the DHQ varied from 70-85%. In both these studies, the DHQ response rates were not statistically different than those from shorter FFQs.

Subar AF, Ziegler RG, Thompson FE, Johnson CC, Weissfeld JL, Reding D, Kavounis KH, Hayes RB for the Prostate, Lung, Colorectal, and Ovarian Cancer Screen Trial Investigators. Is shorter always better? Relative importance of questionnaire length and cognitive ease on response rates and data quality for two dietary questionnairesExternal Web Site Policy. Am J Epidemiol 2001;153(4):404-9.

Subar AF, Thompson FE, Kipnis V, Midthune D, Hurwitz P, McNutt S, McIntosh A, Rosenfeld S. Comparative Validation of the Block, Willett, and National Cancer Institute Food Frequency Questionnaires: The Eating at America's Table StudyExternal Web Site Policy. Am J Epidemiol 2001;154:1089-99.


How is the questionnaire best administered?

We designed the DHQ to be self-administered. There is no reason, however, why an interviewer could not administer it. If possible, we recommend that a staff person review the instrument to check for missing pages or other missing data.


Can the DHQ be administered to children?

The DHQ was developed using national dietary data from adults in USDA's Continuing Survey of Food Intake by Individuals 1994-96 to specify food items and portion sizes. It is not appropriate for administration to children in its current form.


Are there translated versions of the questionnaire?

The DHQ has been translated into Spanish, but there are no other versions translated from English.

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Validation

Has the DHQ been validated?

See the Validation Studies page for information regarding the validation of the instrument.


Is the DHQ considered "validated" if you make changes?

There is no accurate answer to this. It all depends on how much you modify the questionnaire. Small changes are unlikely to affect validation substantially, but if you make many changes to the DHQ, the published validation research may not apply to your new instrument. This may also be true if you are administering the DHQ in specific populations.


Has the DHQ been validated or used in any special population groups?

The DHQ was designed from a general population national dietary survey. These reference data are representative of the entire U.S. adult population. Therefore, you may need to modify the DHQ for use in specific population groups.

Was the DHQ validated for vitamin D intake?

The validation studies do not include vitamin D because vitamin D values were not included in the DHQ Nutrient Database when the studies were conducted. They were subsequently added to the database on January 17, 2003. Given that the DHQ did as well as or better than other widely used questionnaires with respect to validation of other nutrients, there is no reason to think that validation of vitamin D would have been any different.


Has the DHQ been validated for the Hispanic and Asian populations?

The instrument has not been validated in other ethnic populations. We look to the investigators to adapt and use the DHQ in other populations of interest.

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Scanning Equipment

We plan to purchase a scanner for in-house use. What type of scanner would you recommend to get high quality results?

Dozens of vendors offer potential solutions. The software aspect drives the decision process, not the scanner. They would need to find software that fits their profile, then pursue a recommended scanner.

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Nutrient Database

What nutrient database does the Diet*Calc software use?

The nutrient database for the DHQ was created using a data-driven method derived from national dietary data from USDA's 1994-96 Continuing Survey of Food Intakes by Individuals (CSFII). The method is documented in:

Subar AF, Midthune D, Kulldorff M, Brown CC, Thompson FE, Kipnis V, Schatzkin A. An evaluation of alternative approaches to assigning nutrient values to food groups in food frequency questionnairesExternal Web Site Policy. Am J Epidemiol 2000;152:279-86.

The file format required for Diet*Calc is detailed in the Diet*Calc Help System. The help system is installed with the Diet*Calc software (see Download the Diet*Calc Software).


What nutrients or food groups are provided with the Diet*Calc software?

See DHQ Food and Nutrient Database.


Are intakes for vitamin and mineral supplements added to individual nutrient estimates from foods in the outcome analysis? For example, is the value reported for Vitamin C food intake alone or food intake plus supplement intake?

Nutrient estimates from food sources are reported separately from the estimates for vitamins and supplements.

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Calculations

What assumptions does Diet*Calc make regarding foods asked, "in season" vs. "rest of year," or "in summer/winter" vs. "rest of year?"

Diet*Calc's default settings for when frequency questions are asked for "in season" vs. "rest of year," are 1/4 vs 3/4 of a calendar year. For frequency questions asked with the terminology "in summer/winter" vs. "rest of year" the settings are 1/3 vs 2/3 of the year.

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Modifying the DHQ

Can I modify the DHQ by adding or removing food questions?

The software for the DHQ is flexible enough to allow you to add and remove food questions and make other modifications. Keep in mind that you will need to provide nutrient values for any new food questions that you add.


Can I modify the DHQ by adding nutrients?

Yes, you can modify the Diet*Calc food and nutrient database to add or modify nutrients/dietary constituents. The Diet*Calc Database Utility allows you to import nutrient data into a Diet*Calc food database. The utility converts nutrient values expressed as nutrient per 100 grams into the nutrient per serving size format expected by Diet*Calc. The Diet*Calc Database Utility is available with the current version of the software (see Download the Diet*Calc Software).

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Data Quality Issues

How does Diet*Calc handle missing data?

If a respondent does not answer a frequency question (the most critical element in determining intake), the software assumes zero intake even if portion size information is available. Diet*Calc will provide you with summary information about missing values on all the items of the DHQ.


How does Diet*Calc handle inconsistent responses for skip pattern and frequency questions?

If the respondent answers "No" to the question "In the past 12 months, did you eat <food>?" then a zero frequency is given.

Example: The respondent answers "No" to the question "In the past 12 months, did you drink soda?" The respondent then answers "1-2 times per week" to the "soda in summer" question. Soda is assigned a frequency of zero.


How do I decide how to exclude respondents for poor quality data?

Users can decide, based on missing values, energy, or other considerations, which individuals to exclude from analyses. Diet*Calc has no built-in edit or exclusion programs. Future versions of the software will include options for excluding records based on various criteria.


Does Diet*Calc have a mechanism to identify questionnaires with unusual or repetitive response patterns (suggesting that the respondent is not reading the DHQ or taking it seriously)?

This is not built into the software. Different investigators want to do data cleaning different ways: some like calorie exclusions, some like exclusions based on percentile cutpoints of nutrients or missing data, some like to transform data and then exclude, others want to exclude those respondents who did not take the task seriously (however that is defined). By looking at the scanned data file, one can write a program to check issues related to whether an individual always checks the same frequency or portion size. It is our experience that it is difficult to discern these types of errors from kcal exclusions or from those who skip foods that they never consume to begin with. No matter how you look at it, FFQ data are always messy for a few people and prone to measurement error for all respondents. Often many hours are spent trying to develop exclusion criteria, and the conclusions vary. Ultimately, if you exclude extreme outliers based on your nutrient or food group of interest, you are probably in reasonable shape regarding hypotheses you are testing.

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HHHQ and DietSys

Is the DHQ an updated version of the NCI Health Habits and History Questionnaire (HHHQ) developed by Dr. Gladys Block and colleagues?

The HHHQ, previously distributed by the National Cancer Institute, is still available from Dr. Gladys Block who is now at the University of California at Berkeley. The DHQ is a food frequency questionnaire developed more recently by researchers at the NCI.

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