A semiquantitative dietary history questionnaire for Chinese Americans

A Semiquantitative Dietary History Questionnaire for Chinese Americans

MARION M. LEE, PHD, FLORENCE AND REI MIIKE, MPH

LEE, MPH, SOPHIE WANG LADENLA, BS,

An 84&m, semiquantitative dietary history questionnaire was developed for epidemiologic studies of diet and diseases in Chinese Americans. The questionnaire is a 30-minute, face-to-face administered instrument designed especially for assessing mixed dishes; it consists of a food list and requires information on frequency of consumption and portion estimation. A nutrient database wa.s compiled from many sources, but mostly from US Department of Agriculture publications. The relative validity of this food frequency questionnaire was tested among 74 Chinese wOrnen between the ages of 30 and 60 years living in the San Francisco Bay area against a l-day recall deemed a typical day’s diet. Correlation coefficients of nutrients from both methods ranged from 0.2 for total fat to 0.7 for calcium and were all statistically significunt at less than the 0.001 level. Ag reement between these two methods was assessed by the percentage of misclassification of quartile distributions. Around 10% were grossly misclassified and 50% were correct estimates of intake in the same highest quartile, while.73% were correctly placed in the two highest quartiles. This food frequency questionnaire can reasonably estimate the usual dietary intakes among Chinese Americans for epidemiologic studies, bur further validation would be needed. Ann Epidemiol 1994;4: 188-l 97.

KEY WORDS: Diet, mixed dishes, questionnaire, frequency, Chinese Americans.

INTRODUCTION

A semiquantitative dietary history questionnaire was employed in a recent case-control study of dietary factors associated with colorectal cancer among Chinese in China and in North America (1, 2). In a subsequent study, a modified version of this semiquantitative dietary history questionnaire was used with Chinese in Taiwan (3) and concurrently validated for the study of Chinese populations. We describe the procedure used to develop this questionnaire and the development of the database for analyzing nutrient values. The relative validity of the instrument was established by comparing nutrient intakes in the semiquantitative dietary history questionnaire with a typical day’s diet.

MATERIAL AND METHODS

Development of the Semiquantitative Dietary History Questionnaire

Needed was an instrument that could (a) capture the usual dietary intake of Chinese Americans including the fre-

From the Department of Epidemiology and Biostatistics, University of California, San Francisco (M.M.L., F.L., R.M.), and the Department of Health Policy and Research, Stanford University, Stanford (S.W.L), CA.

Address reprint requests to: Marion M. Lee, PhD, Department of Epide- miology and Biostatistics, University of California, San Francisco, CA 94143-0560.

Received May 24, 1993.

quency and quantity of consumption of mixed dishes and (b) enable the ranking of individuals into quartiles of intake for use in epidemiologic studies.

The instrument, to be used in a face-to-face interview lasting not more than 30 minutes on average, consists of a list of 84 food items. Information relating to the frequency of consumption, and quantitative estimate of portion size are requested for each food item. Interviewers can be easily trained to reduce interviewer bias.

Food List

A comprehensive list of 130 food items was compiled, mod- eled after Willett’s semiquantitative food frequency questionnaire (4). Food items contributing to the food list were gathered from the following sources: informal interviews with 20 Chinese men and women about their actual food intake of the preceding day, and direct observation of specific meats, fruits, and vegetables available in the Chinese supermarkets. The food items were selected by the following criteria: The food item must be available and commonly consumed by Chinese Americans, and must contribute an appreciable amount of calories and nutrients of interest with respect to the colon cancer hypothesis (i.e., total fat, vitamin A, beta carotene, and fiber). To limit the instrument to a 30-minute personal interview, through several pilot testings, the food list was shortened to 84 items by compressing a group of foods into one food item because either the foods

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Lee et al. 189 DIETARY HISTORY QUESTIONNAIRE

TABLE 1. Food list of semiquantitative dietary history questionnaire

Food items

No. of times per

d, wk. mo, or v Serving

unit

No. of serving pkg. in dish

(if applicable) Fraction

or multiple

Pork in mixed dishes Pork in unmixed dishes such as pork chop, roast,

charsui, meatballs, meat patty, braised Beef in mixed dishes Beef, veal or lamb in unmixed dishes, including

steak, roast, hamburger, braised Chicken in mixed dishes Chicken in unmixed dishes such as roast, steamed,

braised

Other meat, fish, and eggs Other fowl, any kind ifneeded, such as duck, goose,

turkey, squab Liver, any kind if needed, such as chicken, pork,

beef Other organ meats, any kind if needed, such as

heart, tongue, brains, kidney, tripe Ham, any kind if needed, such as bacon, Canadian

bacon, Chinese ham Cold cuts, any kind if needed, such as salami,

pastrami, bologna, corned beef Pork skin, pigs feet, pigs knuckles Sausages, any kind if needed, such as frankfurters,

hot dogs, Chinese sausage (laap Cheung) Salmon, mackerel, or swordfish Other fish, any kind if needed, such as saltwater

or freshwater fish Shellfish if needed, such as clams, shrimp, lobster,

oyster, crab Omelet, fried/scrambled eggs Other eggs, any kind if needed, such as preserved

eggs, eggs used in baking or cooking Bean curd, any kind if needed, such as soft, dried,

fried, fermented

Dairy products and fats Whole milk if needed, evaporated and condensed

milk Skim or low-fat milk if needed, powdered and

malted milk Ice cream Sherbert, ice milk, or yogurt Cream, any kind if needed, whipping cream, half

and half Cottage cheese Other cheese, any kind if needed, such as cream

cheese used in cooking or eaten alone Vegetable cooking oil Other fat, such as lard, butter, margarine, sesame

oil Low-calorie dressings Mayonnaise and other salad dressings

Starches and sweets Rice Noodles, other pasta, any kind Dark bread, rolls Bran or wheat cereal if needed, unsweetened and

dark brown in color Other cereal (dry or cooked) White bread, rolls Salted Chinese pastry if needed, dumplings, charsui

buns, spring rolls

1 pkg 1 whole or 1 piece

(2 chunks) 1 &g 1 whole or 1 piece

(2 chunks) 1 pkg 1 cut-up piece

Omitted

Omitted

Omitted

Omitted

Omitted

Omitted

Omitted

Omitted

Omitted

1-0~ slice

1-0~ slice

1 piece (2 chunks) 1 link (no model)

4-0~ piece 4-02 piece

Omitted Omitted

1 egg (no model) Omitted Omitted

Omitted Omitted

1 cup

1 cup

‘/z cup = 1 scoop Omitted 1 tablespoon

Omitted

Omitted l-02 slice

Omitted

Omitted Omitted

Omitted Omitted

Omitted Omitted

Omitted Omitted

8-02 bowl = 1 cup 8-0~ bowl = 1 cup 1 slice or roll 1 cup

Omitted Omitted Omitted


190 Lee et al. DIETARY HISTORY QUESTIONNAIRE

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TABLE 1. (Continued)

Food items

No. of times per

d, wk, mo, or y Serving

unit

No. of serving pkg. in dish

(if applicable) Fraction

or multiple

Waffles, pancakes Potato chips, corn chips, pretzels, popcorn, etc. Chinese sweet pastry if needed, bean paste

Omitted

cake/buns Cookies/cakes/pies Chocolate


Vegetables Green beans, peas, snow peas, and other beans Broccoli, any kind if needed, includes Chinese

‘/2 cup

broccoli ‘12 cup Cabbage, any kind and bok choy, if needed,

Chinese and other cabbage and coleslaw Spinach, and any kind of dark leafy greens if

% cup

needed, mustard greens, watercress, kale Asparagus Brussels sprouts Carrots Celery Corn

% cup ‘/z cup % cup % cup % cup ‘12 cup

Peppers, any kind if needed, green, red, sweet and hot

Onions, including green onions, scallions Tomatoes if needed, fresh or cooked, in sauce,

% cup % cup

soup or pasta Lettuce such as leafy and head Turnips, daikon, radishes Cauliflower Bamboo shoots Green squash if needed, zucchini, bitter melon,

Omitted Omitted Omitted Omitted Omitted

winter melon, bottled squash Sweet potatoes, yams, yellow squash, pumpkin as

Omitted

used in pies, soup or cooked White potatoes such as baked, boiled, mashed Fried potatoes/french fries

Fruits and nuts Apples Bananas Pears


Citrus, such as oranges, tangerines, grapefruit Melon, any kind if needed, watermelon,

Omitted Omitted Omitted Omitted

cantaloupe, honeydew Peaches, plums, apricots, nectarines Strawberry, grapes, cherries Papayas or mangoes Avocados Nuts such as peanuts, almonds, walnuts, pecans,

cashews, etc. Peanut butter


Omitted Omitted

Beverages Beer Wine or sherry Liquors, including Chinese and other hard liquors

and liqueurs Tap water Mineral water Tea Decaffeinated coffee such as Sanka, DeCaf Regular coffee Fruit juices, any kind Soft drink Soup, any kind

12-02 glass 4-0~ glass

2 oz (‘/4 cup) Omitted Omitted Omitted Omitted Omitted Omitted Omitted Omitted

Omitted Omitted



Omitted


Omitted Omitted Omitted Omitted


Omitted Omitted

Omitted Omitted Omitted Omitted Omitted Omitted Omitted Omitted

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have similar nutrient values or they are often eaten inter- changeably. For example, ham of any kind includes ham, Canadian bacon, and Chinese ham; sweet potatoes, yams, yellow squash, and pumpkin were combined as one item. The comprehensive food list of 84 items is shown in Table 1.

Frequency Format

Participants had to specify one of the following categories to assess the frequency of intake: number of times per day, week, month, year, or not at all in the past year.

Portion Size

For each food item, a commonly used portion size was specified and participants were asked to describe the usual portion size as a multiple or fraction of the specified portion. Portion size was asked only for food items frequently consumed (more than once a week). Typical Chinese food preparation mixes meat of different cuts (cubes, strips, slices, or chunks) with other foods such as vegetables and noodles. To help respondents describe more precisely their usual portion size, specifically designed three-dimensional, actual-size food models representing the mixed dishes and single food items were used during the interview (Figure 1). For specific instructions for administering the three-dimensional models, see Table 2.

The questionnaire also asks about the type of fat used in cooking meat, fish, and vegetables, and the consumption of visible fat on meat and skin on chicken (Table 3). Al- though seasonal fruits and vegetables are not separated into “fresh in season,” “ canned,” or “frozen” categories, participants were instructed to state the frequency of consuming fruits and vegetables in season and not in season.

191

Development of a Nutrient Database for the Chinese American Diet

The nutrient database was mainly compiled from US De- partment of Agriculture (USDA) publications (5,6). Other sources included published and unpublished data and food tables (7-9). Some Chinese specialty foods such as meat dumplings and sweet bean dessert were incorporated by using recipes from a Chinese cookbook (10). The calories and nutrient values of protein, carbohydrates, and fat of these Chinese recipes were also obtained from this ethnic cookbook (IO).

The database provides 100% of energy and nutrient composition values for protein, lipid, carbohydrate, saturated and polyunsaturated fatty acids, cholesterol, calcium, phos- phates, and vitamin C. But for vitamin A and beta carotene, the database only provides about 80% and for dietary fiber, about 60%.

Each of the 84 food items was specified in a commonly consumed portion size, and most food items were represen- tative of a group of similar foods. We assigned the quantitative nutrient values to each of the 84 food items with the following steps: (a) Within each food item, those cuts or preparation methods commonly used by Chinese Ameri- cans were selected; (b) each selected food within a category was adjusted to the same portion size; and (c) the mean nutritive values of the selected foods were calculated. Thus, the nutritive values of a food item were represented by the mean nutritive values of all the specific foods included within that category. For example, to assign a nutritive value to the food item “pork in mixed dishes (2 02)” we used the nutritive values of different cuts of pork (2 oz each of pork blade, center loins, and top loins) and used specific commonly used preparation methods (lean and fat pan- fried, and lean pan-fried) and averaged them to represent the nutritive value of this food item.

FIGURE 1. Three-dimensional, actual-size food models. (A) Different cuts of meats (clockwise: chunks, strips, slices, and cubes). (B) Mixed dishes.

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TABLE 2. Snecific instructions for administering three-dimensional models

I am going to ask you a few questions regarding the foods you usually ate during 19_ (last year). As I read each food item, please tell me how often you ate it. You may answer in terms of number of times per day, per week, per month, or per year that you ate the food, or that you never ate the food.

Meat Mixed dishes: Record answers on chart on page 13. a. During 19_, how often did you eat -! Refer to food item; record number of times per d, wk, mo, or y.

Ask (b-d) only if food item was eaten once a week or more.

b. Show cubes, strips, slices, chunks. Did you most frequently eat _ that was cut in cubes, in strips, in slices, or in chunks? Do not record answer.

Mix 1 cup of green beans and 1 pkg of meat on plate (1 pkg = 20 cubes, or 10 strips, or 8 slices, or 2 chunks), and say

c. The green beans represent whatever you ate with pork/beef/chicken, such as vegetables, noodles, etc. Is this a large enough proportion of pork/ beef/chicken to other foods in the mixed dish that was usually served?

If yes, record one serving package. Go to I‘d.” If no, add 1 pkg of meat at a time until proportion is satisfactory, or excessive, then record number of serving packages.

d. How much of the pork/beef/chicken in this dish did you yourself eat each time? Record fraction or multiple of meat eaten. Clear plate.

The following describes samples of the selections repre- sentative of a particular food item: (a) Meat (pork, beef, veal, or lamb) in mixed dishes included different cuts (lean, lean and fat) pan-fried, sauteed, stewed, or braised; (b) meat in unmixed dishes included two types of fat content and the cooking methods roasted, braised, fried, or broiled; (c) chicken included light and dark meats, with or without skin, fried, roasted or stewed; (d) fowl included ducks, goose, and turkey roasted with and without skin; (e) other organ

TABLE 3. Questionnaire on fat consumed

meats included pork brain, ears, kidney, chitterlings, and beef tongue; (f) fish included bass, halibut, flounder, tuna, and sturgeon oven-fried, baked, boiled, canned, and steamed; (g) other eggs included one medium boiled chicken egg, one salted duck egg, and one preserved duck egg; and (h) cheeses with a range of 6 to 9 g of fat content per ounce, such as cheddar, cream cheese, Gouda, mozzarella, Parme- san, processed American, and Swiss.

For some particular foods such as meat, fish, and vegeta-

Seldom Often Food not Do not Never (< % the time) (2 r/z the time) Always eaten recall

a. When you ate meat, how often did you trim the fat off 1 2 3 4 5 9 the meat?

b. When you ate meat, how often was it cooked in oil, butter, 1 2 3 4 5 9 lard, bacon fat, or margarine?

c. When you ate chicken, how often did you eat it with the 1 2 3 4 5 9 skin on it?

d. When you ate chicken, how often was it cooked in oil, 1 2 3 4 5 9

butter, lard, bacon fat, or margarine? e. When you ate fish, how often was it cooked in oil, butter, 1 2 3 4 5 9

lard, bacon fat, or margarine? This includes adding oil to steamed fish.

f. When you ate vegetables, how often did you add butter/ 1 2 3 4 5 9

margarine to them? g. When you ate vegetables, how often did you eat them 1 2 3 4 5 9

stir fried? h. When you ate beef, how was it usually cooked?

(Read choices l-5)

1 = Rare 2 = Medium rare 3 = Medium 4 = Medium well 5 = Well done 6 = Variable 7 = Did not eat red meat 9 = Do not recall

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bles, appropriate calories and nutrient values (total fat, saturated fat, monosaturated and polyunsaturated fat) were adjusted based on the frequency of adding fat (always, often, or seldom) and the type of fat used in cooking these foods and the frequency of consuming marbled fat in meat and skin on chicken (see Table 3). For example, the amount of fat added to a specific item in one serving size (2 oz of chicken) was based on the frequency of adding fat to cooking (“always” [ 15 g], “often” [lo g], or “seldom” [3 g]), the type of fat used in cooking (adding butter or margarine or stir- fried with oil), and the frequency of consuming chicken with skin (always, often, seldom, or never). The calories and fat values of the particular food item were subsequently adjusted.

Methods for Validating the Semiquantitative Dietary History Questionnaire

Subjects were 81 middle-aged Chinese women who partici- pated in the University of California Breast Disease and Breast Fluid Study (11) from 1989 to 1990. They either were recruited from the original 102 study subjects at the San Francisco Chinatown Health Fair or were employees at the University.

The semiquantitative dietary history questionnaire was administered to each participant for their usual frequency consumption of 84 food items over the past year. The participants also reported their average portions of items consumed more than once per week. To facilitate estimating portion sizes, food models of Chinese-style and Western- style meals as they appear when served were displayed. Parti- cipants described their customary meat/vegetable ratio of the simulated foods by showing their usual portion size of the mixed food items. It was assumed that I-oz volume of simulated food equals 1 oz of cooked food. The interview took 25 to 30 minutes to complete. Participants were also asked to recall a typical day’s diet during the past month. Interviewers were instructed to say, “We would like to know about your usual food intake. Think about a typical day during last month; it could be a workday or a nonworking day. Please tell us everything you ate from the time you got up in the morning until the time you went to bed. You need to include everything you ate away from home, at work, or other places and don’t forget foods eaten in between meals.” The sequential administration of the two dietary assessment methods to the same individual raises concern that one method may influence responses to the other. Therefore, the typical day’s diet was randomly asked either before or after administration of the dietary history questionnaire. The typical day’s diet recall took about 5 to 10 minutes. The method of quantifying portion sizes used for the semiquantitative dietary history questionnaire was also used for the typical day’s diet. The same food models and measuring cups were displayed at the interviews.

Nutrient Intake

Both data from the dietary history questionnaire and the typical day’s diet were coded and analyzed using the nutrient database developed for this study. The nutrient values of the 84 food items were obtained by multiplying the frequency by the serving size of each food consumed and summing all quantities to yield a single value for each nutrient. Values of total food energy and intake of fat and its components (saturated, monosaturated, and polyunsaturated fatty acids) were adjusted to reflect reported frequency and type of fat(s) used in cooking.

Statistical Analyses

Descriptive statistics, means, and standard deviations of each nutrient measured by the two methods were calculated and tested by the two-tailed t test. Spearman and Pearson correlation coefficients were used to compare nutrient intakes for individual subjects as calculated from the questionnaire and from the typical day’s diet. Spearman nonpara- metric correlation coefficients were found to be similar to Pearson coefficients; thus, only the latter are presented. To evaluate the agreement between the two methods, the population was cross-classified by quartiles and the extreme quartiles from each method were compared: the highest according to the questionnaire with the highest according to typical day’s diet. The extreme highest two quartiles for the two methods were also compared. The percentages of exact matches and within-quartile matches were calculated.

RESULTS

Out of the original 102 Chinese American subjects who were in the breast fluid study, 81 women agreed to partici- pate in this study and 74 (91%) completed both dietary assessment instruments. The women were middle-aged, middle-income Chinese (Table 4). Eighty-two percent were foreign born, the majority were high school graduates, and their average body mass index was 22 kg/m*.

In general, nutrient intakes estimated by the frequency method were consistently higher than those estimated by the typical day’s method, with the exception of vitamin C (Table 5). The nutrients that differed significantly by the two methods were total calories, total fat, saturated fat, cholesterol, vitamin A, and beta carotene. Other nutrients such as protein, carbohydrate, calcium, fiber, and vitamin C and percentage of fat did not significantly differ by the two assessment methods. We did not request information about subjects’ supplemental use of vitamin C, vitamin A, beta carotene, or multiple vitamins.

Although the correlation coefficients comparing nutrient intakes by the two methods were all statistically signifi- cant from zero, the intent was not to test statistical sig

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TABLE 4. Characteristics of Chinese women completing the dietary history questionnaire and the typical day’s diet record

Characteristic

Sample total (n)

Age (Y) Education (y) Foreign born (%) Income (%)

< $10,000 $lO,OOO-$29,000 $30,000-$69,000 2 $70,000

Weight (lb)” Height (in) Body mass index (kg/m’)”

’ Mean e standard deviation.

74 40.7 & 11.9 13.0 f 5.4 81.9

19.7 31.9 31.8 12.1

115.8 + 15.9 61.7 + 2.1 21.7 f 3.3

nificance but to compare quantitatively the two dietary methods. The coefficient was lowest for total fat and highest for calcium, ranging from 0.21 to 0.66 with an average of 0.45 (Table 6).

Another approach to examine the agreement between the two dietary methods is to cross-classify the population distribution by quartiles; see Table 7 for a summary of such joint classification. Overall, 50% of subjects in the highest quartile of absolute nutrient intake computed from the diet history method were also in the highest quartile based on the typical day’s method, and 73% were in the highest one or two quartiles. On average, only 10% were misclassified into extreme quartiles. Total fat was the nutrient with the least agreement on the highest quartile comparison, while cholesterol demonstrated the most agreement. It is notewor- thy that there was 93% agreement of estimated total calories using the highest two quartiles and that 0% was misclassified by the lowest extreme quartile.

TABLE 5. Mean absolute nutrient intakes (5 standard deviation) estimated by dietary history questionnaires and by typical day’s diet record (n = 74) and P value from paired t test

Dietary history questionnaire Typical day diet P

Total calories (kcal) 1772 2 550.4 1570 !z 346.3 0.01 Total fat (g) 71.4 2 30.0 52.4 r 17.5 0.00 Saturated fat (9) 18.5 f 9.5 14.4 f 6.5 0.00 Cholesterol (mg) 226.4 f 172.1 176.8 2 116.7 0.04 Protein (g) 82.9 f 44.1 76.6 f 28.2 0.30 Total carbohydrate (g) 203.4 + 62.2 197.8 5 59.1 0.58 Crude fiber (g) 4.0 f 1.7 3.5 f 1.8 0.08 Calcium (mg) 566.9 2 250.7 541.3 2 274.7 0.56 Phosphorus (mg) 1114 f 402.1 1010 2 315.8 0.08 Vitamin C (me) 121.5 f 53.1 133.5 * 88.7 0.32 Vitamin A (IU) 7996 + 4173 6153 + 4572 0.01 Beta carotene (mg) 5483 f 3215 4211 2 3660 0.03 % Fat 36.2 f 4.9 30.1 * 4.5 0.35

TABLE 6. Pearson correlation coefficients comparing nutrient intakes from the dietary history questionnaire with a typical day’s diet record (n = 74)

Nutrient Correlation coefficient

Total calories 0.50 Total fat 0.21 Saturated fat 0.37 Cholesterol 0.51 Protein 0.56 Total carbohydrate 0.37 Crude fiber 0.28 Calcium 0.66 Phosphorus 0.53 Vitamin C 0.50 Vitamin A 0.46 Beta carotene 0.40 % Fat 0.45

DISCUSSION

An instrument developed for one population may not be applicable to another, especially for ethnic groups that ex- hibit culturally influenced dietary habits. Our semiquantitative dietary history questionnaire was developed for Chinese Americans. Several limitations should be considered. A database like the Second National Health and Nutrition Ex- amination Survey (NHANES II) (12-14) does not supply a food list specific to Chinese or Asian Americans. The USDA nutrient database values (5) were derived by food preparation methods not commonly used by Chinese, therefore raising some concern about the accuracy of nutrient composition. Furthermore, the nutrient composition table of Asian foods has not been updated (8) recently, and data on fiber and vitamin A components were incomplete.

The nutrient intake by the participants in this study was similar to that of Chinese female control subjects reported in a previous study that employed the same dietary assessment method (1).

Assuming our participants were moderately active and their body weight (116 lb) was stable, the estimated energy requirement to maintain their body weight was 1740 kcal (15). This energy requirement was found to be similar to the actual caloric intake estimated by our semiquantitative dietary history method, 1772 kcal.

Validation by comparing the questionnaire method to a “gold standard” would be ideal. This would involve comparison of the semiquantitative dietary history questionnaire with several food records taken over a period of 1 year, as suggested by Willett and colleagues (3) and Hankin and coworkers (16). However, due to the limitation of our resources, the use of multiple records or recalls as compara- tive measures was not feasible. To assess the relative validity of the semiquantitative dietary history questionnaire in our study, we chose the typical day’s diet during the last month as a comparison method. Since the semiquantitative dietary

ASP Vol. 4, No. 3 Lee et al. 195 May 1994: 188-197 DIETARY HISTORY QUESTIONNAIRE

TABLE 7. Comparison of absolute nutrient intake from the dietary history questionnaire and typical day’s diet record based on joint classification by quartiles

Highest quartile on dietary history questionnaire

Nutrient

Highest quartile on typical day record

11 %

Highest 2 quartiles on typical day record

11 %

Lowest quartile on typical day record

II %

Total calories Total fat Saturated fat Cholesterol Protein Total carbohydrate Crude fiber Calcium Phosphorus Vitamin C Vitamin A Beta carotene Mean

8/14 5/15

10/15 11/16 8/17 8/18 6/15

lo/l8 7/16 7115 7116 7/16

57.0 33.3 66.6 68.7 47.0 44.4 40.0 55.5 43.7 46.7 43.7 43.7

49.8

13/14 9/15

11/15 14/16 12/17 13/18 9/15

16/18 13/16 l1/15 IO/16 9/16

92.8 o/14 0 60.0 2/15 13.3 73.3 l/15 6.7 87.5 l/16 6.2 70.6 2/17 11.7 72.2 3/18 16.6 60.0 3/15 20.0 88.8 l/18 5.5 81.2 O/16 0 73.3 l/15 6.7 62.5 3/16 18.7 56.2 3/16 18.7

‘3.2 10.3

history questionnaire estimated the usual diet during the past 12 months, the typical day’s diet during the past month was chosen to represent a similar time frame. A typical day’s diet may present a more usual dietary pattern than a single 24-hour recall. In fact, due to measurement errors, several multiple 24-hour diet records are needed to represent a “true” usual intake (17, 18). The moderate correlation that resulted in our study can also be partially explained by the limitations of a typical day’s diet.

Measurement Errors

Major sources of error associated with the semiquantitative dietary history questionnaire include recall, perceptions of usual portion size, and possibly the restrictions imposed by a fixed list of food items.

When a dietary method is chosen as a reference for comparison in a validation study, dependent errors associated with both methods can falsely elevate correlations, because both methods have the same type of error in requiring recall ability. Multiple diet records over time are often used for validating a food frequency questionnaire (3, 16, 19), because they are the least likely to involve dependent errors. Unlike the food frequency method, they do not depend on memory; that is, foods are recorded on a daily basis rather than reported or recalled. However, independent errors associated with diet records and food frequency questionnaires tend to underestimate the validity of the food frequency questionnaires (low correlations), because food records might only represent diets assessed at a few points during the study period. Therefore, the selection or design of a dietary standard reference remains a challenge.

The use of a typical day’s diet record for evaluating our semiquantitative dietary history questionnaire might be suboptimal because both methods are subjected to the same

errors (dependent error) such as relying on memory and perceptions of serving size. Another source of independent errors associated with the typical day’s diet record is the inability of the respondent to capture and to construct a typical day’s diet from variations of daily food intake cov- ering the past 30-day period. The moderate correlation that resulted in our study could be partially explained by this error. However, because the two instruments (food frequency questionnaire and typical day’s diet) were administered on the same day, the participant might become sensi- tized to her diet by having completed one instrument earlier, thus affecting her recall for the second method. As a result, our findings might have been biased in favor of higher correlations between the two. The magnitude of such errors needs to be further investigated.

Another source of measurement error is the limitation of the nutrient database. Both methods used in assessing nutrient intake may not be precise because the nutrient composition data were unrepresentative of the foods actu- ally consumed.

Since there is no perfect dietary assessment method that can be used as a reference for validation, and because we had limited resources to conduct repeated interviews, as well as varying levels of motivation and education among respondents, our selection of the typical day’s diet record for comparison with our semiquantitative dietary history questionnaire was considered the most practical in the situa- tion.

Adjustment for Total Calories

Use of calorie-adjusted intakes in the analysis can compen- sate for the effect of errors in energy intake, and can also help reduce between-person variation due to general over- reporting or underreporting (20, 21). The use of nutrient

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densities in the analysis of the diet tends to control biases resulting from inaccuracy in estimation of portion size or frequency of consumption (22). Discrepancies in results using calorie-adjusted nutrients values in validating studies have been reported (3, 19, 22, 23). Willett (3) showed that adjusting for calories for macronutrients resulted in improved correlations and relative ranking in validation studies, while Pietinen and coauthors (19) reported only slight improvement after adjustment for energy intake. Flegel and Larkin (23) found that respondents did not report macronutrients in similar proportions on the two instruments used in their validation study. Therefore, calorie-adjusted macronutrient values improved the correlations and relative ranking only slightly. Stein and associates (22) found that the correlation between Willett’s semiquantitative food frequency questionnaire and 240hour dietary recalls generally decreased when nutrient intakes were adjusted for calories; when data were expressed in nutrient densities, agreement was high for several nutrients only.

generally satisfactory and were fairly comparable with other investigations among other populations. Though this semiquantitative dietary history questionnaire may not provide precise absolute nutrient intake, it is capable of ranking individuals by relative levels of nutrient intake. Its advan- tages-ease of administration, light respondent burden, and the potential to be modified for telephone interview or for self-administered survey including mail survey-make this instrument feasible for large-scale studies. Our questionnaire can reasonably assess the usual dietary intakes of Chi- nese Americans who are either recent immigrants or US born (second or several generations). Further validation by other investigators would be most helpful, so that later it can be appropriately employed by other epidemiologic studies of diet and diseases of this ethnic population.

We did not use energy-adjusted values or nutrient densities for the following reasons: (a) Discrepancies in agreement between methods using calorie-adjusted values were found in previous studies (3,19,22,23). (b) The female respondents in our study were mostly middle-aged women, their body weight was in a tight range and had been quite stable during the study period (none had substantial weight gain or loss), and they did not alter their dietary intake during the study period. Therefore, their total energy and macronutrient intakes should be stable. (c) The nutrients of special interest in this study were micronutrients such as beta carotene, vitamin A, and fiber, which are not energy related. (d) The percent of calories from fat, protein, and carbohydrates reported between our two methods (dietary history questionnaire versus typical day’s diet) differed only slightly (fat, 36.35 versus 30%; protein, 18.7% versus 19.5%; carbohydrate, 45.5 versus 50.4%), so that adjustment of calories would not improve the correlations.

This research was supported by grant PO1 CA 13556-18 from the National Cancer Institute, Bethesda, MD. The authors thank Drs. Alice Whitte- more, Anna Wu-Williams, and Nicholas Petrakis and Ms. Christine Choy for their assistance.

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A semiquantitative dietary history questionnaire for Chinese Americans