Dietary Assessment in Epidemiology: Comparison of a Food Frequency and a Diet History Questionnaire with a 7-Day Food Record

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1 Ameican Jounal of Epidemiology Copyight O 996 by The Johns Hopkins Univesity School of Hygiene and Public Health All ights eseved Vol. 4, No. 9 Pinted In U.SJU. Dietay Assessment in Epidemiology: Compaison of a Food Fequency and a Diet Histoy Questionnaie with a 7-Day Food Recod Meea Jain, Geoffey R. Howe, and Thomas Rohan The validity of two types of diet assessment methods, a setf-administeed food fequency questionnaie and an inteviewe-administeed detailed diet histoy, was assessed elative to a 7-day food ecod on a population-based sample of 95 men and 8 women in Toonto, Canada, between May 989 and July 99. Each study subject completed both questionnaie methods, a food fequency questionnaie and an intevieweadministeed diet histoy, as well as a 7-day food ecod in a cossove design. Data wee analyzed fo both unadjusted and enegy-adjusted nutients to estimate Peason's and intaclass coelations and ageement within categoies. Mean values fo the intake of most nutients assessed by the two questionnaie methods wee simila. Aveage, enegy-adjusted Peason's coelation coefficients fo men between a food fequency questionnaie and a 7-day food ecod wee.55 fo maconutients and.48 fo mlconutients compaed with.47 fo maco- and.48 fo miconutients between an inteviewe-administeed diet histoy and a 7-day food ecod. Fo women, they wee.48 fo maco-and.54 fo miconutients between a food fequency questionnaie and a 7-day food ecod and.46 and.49, espectively, between an inteviewe-administeed diet histoy and a 7-day food ecod. The enegy-adjusted Peason coelations wee geneally highe than wee the enegy-unadjusted Peason coelations and the intaclass coelations. The pesent study suggests that a food fequency questionnaie is compaable with an inteviewe-administeed diet histoy as a pedicto of nutients as estimated fom a 7-day food ecod. Am J Epidemiol 996;4:95-6. diet; diet suveys; epidemiologic methods; questionnaies In epidemiologic investigations designed to assess the elation between diet and disease, thee is a citical need fo valid and pecise methods fo assessing longtem dietay intakes. The diet histoy (i.e., questioning espondents on the fequency and amount of thei consumption of egulaly eaten foods on a usual basis as opposed to methods based on an exact ecall of diets o a ecod of diets) has been the method most commonly used in such eseach in the past two decades. Othe methods of dietay assessment (e.g., food ecods with o without weighing and duplicate samples of meals) ae often not suitable fo epidemiologic investigations. Such methods ae intusive, and they may cause an individual to change his/he diet, ae expensive, and, when applied to a lage numbe of study subjects, may esult in a lowe esponse ate (, ). Two appoaches to the diet histoy method have geneally been used. In the fist method, an inteviewe administes the questionnaie, wheeas in the Received fo publication May,995, and in final fom Febuay 4, 998. Fom the National Cance Institute of Canada (NCIC) Epidemiology Unit, Depatment of Peventive Medicine and BiostatistJcs, Univesity of Toonto, Toonto, ON, Canada. second, the questionnaie is completed by the subjects themselves. The fome method geneally allows fo assessment of moe individual food items than the latte, since an excessive numbe of food items on a self-administeed questionnaie can make this less acceptable to study subjects. Potentially, theefoe, the inteviewe-administeed diet questionnaie might be expected to be moe pecise in estimating nutient intakes; howeve, the self-administeed diet questionnaie is geneally the only method that is logistically feasible fo lage numbes of study subjects as, fo example, in a cohot study. To the best of ou knowledge, only one study () has diectly compaed the validity of the two appoaches on the same individuals, i.e., an inteviewe-administeed and a self-administeed diet questionnaie against a standad method (multiple 4-day food ecods), and concluded that the self-administeed method has a easonably good ability to place individuals along the distibution of enegy and nutient intake, the basic citeion of validity fo studies of diet-disease elations. The cuent investigation was designed to compae the two questionnaie methods (an inteviewe-administeed diet histoy and a setf-administeed food fequency questionnaie) against a 7-day food ecod, Downloaded fom by guest on 6 Octobe 8 95

2 954 Jain et al. teating the latte as the "gold standad." The pimay objective of the study was to assess whethe the moe expensive and time-consuming inteviewe-administeed questionnaie is justified in tems of inceased validity and pecision as compaed with the less expensive self-administeed questionnaie. MATERIALS AND METHODS Study subjects The study included paticipants aged 5-79 yeas who wee inteviewed between May 989 and July 99. The paticipants wee dawn andomly fom a population-based listing of men and women in metopolitan Toonto, and the sample was selected so that the age distibution of the paticipants was faily typical of that of subjects who might be included in a case-contol study of diet and some chonic disease, such as cance. The initial appoach to study subjects was by telephone. A minimum of six phone calls, at diffeent times and on diffeent days, was made befoe a failue to contact was accepted. A total of 6 potentially eligible subjects who wee still esident in the study aea wee initially contacted, of whom 6 ageed to paticipate. Howeve, of these individuals did not complete the full set of inteviews, so subjects (95 men and 8 women) wee included in the analysis. Questionnaies Each individual in this study was asked to complete the following thee dietay methods in a peestablished design sequence, descibed late. Self-administeed food fequency questionnaie. This questionnaie elicits infomation about food items in tems of the fequency and amount of consumption of each food item, on aveage, duing the past months. Respondents ae asked to indicate thei fequency of consumption of items pe day, pe week, o pe month, and the questionnaie contains a specific column in which the espondent can indicate that a food item is eaten less fequently than once a month. Potions fo a standad size seving ae given next to each item listed. The questionnaie also contains thee sets of pictues, one each fo ice, meats, and chicken. Each set contains thee diffeent potion sizes of the item as a small, medium, o lage seving. These wee measued in elation to a 9-inch-diamete ( cm) dish holding the item. All potions wee standadized by the study nutitionist, and the aw and cooked weights of these items wee taken into account duing coding and nutient analysis. An open-ended section at the end of the questionnaie allows individuals to epot any othe fequently eaten foods not listed on the questionnaie. In addition, thee ae sections with questions on vitamin and mineal supplement use; the type of fat o oil used in cooking, baking, and fying; the timming of visible fat on meats and chicken; cuent and past height and weight; and physical activity at wok and at leisue. An inteviewe-administeed diet histoy. This questionnaie has been descibed in detail elsewhee (4, 5). It elicits the usual fequency of consumption of ove food items pe day, week, o month, ove the past months; diei method of pepaation; and all additions, such as suga in coffee, and amount. Quantitation is based on geometic food models made of papie-mjlche\ wood, and plastics in the fom of cups, bowls, mounds, balls, spoons, etc., of vaious sizes and shapes. Seven-day food ecod. A booklet was given to the paticipants to ecod eveything they ate o dank ove a peiod of 7 consecutive days. Detailed instuctions wee given by the inteviewe to the paticipant to ecod all additions, no matte how small, method of cooking, type, and band names of vaious foods and supplements. Illustations wee povided on metic to impeial convesions and vice vesa, use of household measuing cups and spoons, ules, etc., to help the ecoding pocess and quantitation. Paticipants wee not equied to weigh foods but wee asked to measue the volume of the bowls, cups, etc., that they nomally used to help assess potion sizes. In addition to the dietay assessments, a shot pesonal and medical histoy questionnaie was administeed to all espondents by the inteviewe afte they had completed the inteviewe-administeed diet histoy. This contained questions on the date of bith, education, occupation (cuent and usual), smoking, ethnicity, and pesonal and family histoy of heat disease, cance, and diabetes. Pocedues All inteviews wee conducted by tained inteviewes in the paticipants' homes at a time convenient to them. Regula quality assuance checks wee made to ensue that standad methods wee being pacticed by all inteviewes at all times. Paticipants wee andomized into two goups of equal numbes of men and women in a cossove design to enable measuement of any bias esulting fom the "taining" effect of one method on anothe. In the fist goup, the inteviewe-administeed diet histoy was administeed fist, and the 7-day food ecod was then initiated. The food fequency questionnaie was then completed month late. An inteval of month was chosen to educe any taining effect and memoy influence of one method on anothe. In the Am J Epidemiol Vol. 4, No. 9, 996 Downloaded fom by guest on 6 Octobe 8

3 Compaison of Diet Assessment Methods 955 second goup, the food fequency questionnaie was completed fist, and the 7-day food ecod was then initiated. The inteviewe-administeed diet histoy was completed month late. cs CD * Analysis Individual nutient intakes fo each dietay method wee calculated by using a data bank based on Handbook No. 8 of the US Depatment of Agicultue (6), modified and expanded fo Canadian foods. Nutients analyzed included enegy, potein, cabohydates, fats and fatty acids, mineals, and vitamins. Intake fom vitamin and mineal supplements was not included in the pesent analysis since this analysis focused on dietay nutients only. Most nutient distibutions wee skewed towad highe values; theefoe, all vaiables wee log tansfomed befoe analysis. In addition to compaisons based on absolute nutient intake, compaisons wee also made using enegy-adjusted nutient intakes (, 7). Enegy adjustment was caied out by egessing the nutient (dependent vaiable) and the enegy intake (independent vaiable), as measued by the same instument. The esiduals fom the model wee then added to the log of the sample mean of that nutient, i.e., the nutient intake at mean caloic intake, and the sum was then exponentiated. This total was taken as the enegy-adjusted nutient intake. Aveage daily intakes of nutients wee computed fom the 7-day food ecods befoe calculating the enegy-adjusted values. Peason's coelations and intaclass coelations wee computed to compae any two dietay assessment methods fo both unadjusted and enegy-adjusted nutients. In analysis of vaiance, blocks of two methods wee consideed as betweeninstuments (o within individual) vaiation, while blocks of subjects wee consideed as betweenindividuals vaiation. In addition to the compaisons based on continuous vaiables, nutient intakes wee categoized by quatiles to assess ageement within categoies between any two methods. RESULTS The chaacteistics of the study subjects including age, height, weight, smoking, and disease status ae shown in table. The means and standad deviations fo the vaious nutients fo the thee dietay methods ae shown in table fo men and in table fo women. Thee wee no significant diffeences in the mean nutient intakes between the two goups defined by the cossove design. Neithe was thee evidence that coelations between the two questionnaie methods and the 7-day food ecod diffeed between the i I XI to f "o 8 s. CNI -? si 9 P AA A q CNI CNJ CNI ffl i co q If) co 8 S A^ 8 (O O * CO AJ, Downloaded fom by guest on 6 Octobe 8 Am J Epidemiol Vol. 4, No. 9, 996

4 Dietay fbe (fl).7 (8.5) 5. (9.7) 9.5(4.) Vitamin C. (59.) 96.9 (.) 5.4(.7) vitamin C. (68.8) 5.6(6.) 95.9 (88.7) Cholesteol (mfl) 5.7 (5.8) 45. (7.5). (6.).5. VSamlnE.(.) 5.7(.) 9.(.5) Cholesteol 74. (.).6 (8.4) 5.5(5.).8. TABLE. Mean dally nutient Intakes of 95 men based on thee dietay assessment methods, Toonto, Canada, * FFQ* IDH* Enegy (teal),76 (647)f,6 (96),55 Total fat 9.(.4) 9.6 (47.6) 94.(47.) Satuated tat (fl) 4.(5.) 4.6(8.8).7(7.9) Olete add (fl) 7. (.9) 4.8 (8.5) 6.(8.) Unotelc add (8). (6. 5. (8.) 4.5 (.9) Potetn (a) 87.6 (6.5) 99.9 (6.6) 88.8 (5.9) Cabohydate (fl) 55.4(8.) 8Z8 (.).8(.5) FFQ as % of IDH as % of Z Calcium Ion TNamln Ftbodavf) Nladn Vitamin A Retlnol Beta caotene FFQ IDH 8.9 (66.7) (499.8),.7(749.).9 (4.) 7. (6.) 5.7(5.4).8(.7).6(.).(.).8(.7). (.).(.).7(7.4) 4.7(9.).9 (8.9) 6,648(4,7) 9,7 (6,5) 8,4 (,58),954(,99),47 (4,56),679(,44),5(,7) 5,69 (,67) 4,979 (,5) FFQ as % of IDH as % of *, 7-day food ecod; FFQ, self-administeed food fequency questionnaie; IDH, inteviewe-administeed diet histoy, t Numbes in paentheses, standad deviation. TABLE. Mean dally nutient intakes of 8 women based on thee dietay assessment methods, Toonto, Canada, * FFQ* IDH* Enegy (kcal),744 (55)t,7(675),5(,) Total fat 7.4 (.7) 9.4(.5) 7.8 (9.7) Satuated tat (a).(4.7).5(.9) 4.(.5) Olelc acid (g) 8. (.5) 4. (.) 6. (.) Unotelc acid (a) 8.5 (4.6).5 (6.).8(9.9) Potein 7.9 (.) 89.5 (.4) 8. (4.8) Cabohydate 6. (66.7) 49.4 (8.5) 78.(.) FFQ as % of IDH as % of Dietay fbe 8.5 (7.4) 4.7 (.4) 7. (5.7) Vol. 4. No. 9. FFQ IDH FFQ as % of IDH as % of Calcium 7. (54.7) 95.5 (458.),6.4(69.) Ion.5(.) 5.(4.8).9(6.) TNamln. (.4).4(.5).5(.8) FBboflavIn.5(.6).9(.8).(.) (4.9).7 (6.7). (.4).4 8. Vlamtn A 6,46 (4,89),654 (5,87) 8,97 (7,777) Retlnol,569(,747),8 (,),8(84) Beta caotene,666 (,5) 6,87 (4,) 5,958(6,) *, 7-day food ecod; FFQ, self-administeed food fequency questionnaie; IDH, inteviewe-administeed diet histoy. t Numbes in paentheses, standad deviation. VRamlnE 7.8 (8.).9 (.7). (9.6)

5 Compaison of Diet Assessment Methods 957 two goups (data not shown). Theefoe, data fom both goups wee combined fo all analyses. In geneal, the mean nutient intakes as assessed by the two questionnaie methods ae highe than the means based on the 7-day food ecods. Nutient means based on the two questionnaie methods ae geneally within ±5 pecent of each othe. Howeve, estimates fo fat, potein, and cholesteol ae somewhat lowe when based on the inteviewe-administeed diet histoy as compaed with the food fequency questionnaie, wheeas estimates fo seveal nutients associated with fuit, vegetable, and ceeal intakes, such as vitamin C and fibe, ae somewhat highe when based on the inteviewe-administeed diet histoy. Thee was no consistent patten in tems of which questionnaie method compaed bette with the food ecods. Peason's coelation coefficients and intaciass coelation coefficients ae shown fo enegyunadjusted and enegy-adjusted nutients fo men in table 4 and fo women in table 5. Among men (table 4), the enegy-adjusted Peason coelations between a 7-day food ecod and a food fequency questionnaie anged fom.8 to.7, with easonably good coelations of above.5 fo total fat, satuated fat, oleic acid, linoleic acid, total cabohydates, dietay fibe, cholesteol, calcium, iboflavin, niacin, etinol, vitamin C, and vitamin E. The coelations fo potein, ion, thiamin, total vitamin A, and beta caotene wee somewhat lowe. An aveage coelation of.55 fo maconutients and.48 fo miconutients was obseved. The enegy-adjusted Peason coelations wee geneally highe than wee the unadjusted Peason coelations and the intaciass coelations. This esults because the eduction of coelated measuement eo fo total enegy and the maconutients exceeds the eduction in between-individual vaiation fo nutient intake caused by contolling fo total enegy intake (7). Similaly, when compaisons wee made between an inteviewe-administeed diet histoy and a 7-day food ecod fo men (table 4), the enegyadjusted Peason coelations anged fom. to.7, with easonably good coelations fo total cabohydates, dietay fibe, cholesteol, calcium, etinol, vitamin C, and vitamin E. The aveage coelations wee.47 fo maco- and.48 fo miconutients. The unadjusted Peason coelations and intaciass coelations in this case wee not much lowe than wee the enegy-adjusted Peason coelations. In fact, the unadjusted Peason coelations wee highe fo all fat nutients, etinol, and vitamin E. Among women (table 5), the enegy-adjusted Peason coelations between the food fequency questionnaie and the 7-day food ecod anged fom.8 to.67, with values of.5 o geate fo satuated fat, dietay fibe, calcium, ion, iboflavin, niacin, total vitamin A, beta caotene, vitamin C, and vitamin E. A TABLE 4. Peason's coelation coefficients () and intaciass coelations ( { ) between two questionnaie methods and 7-day food ecods fo men (n = 95), Toonto, Canada, Nutient Enegy (kcal) Total fat (g) Satuated fat (g) Oleic acid (g) Unoletc acid (g) Potein (g) Cabohydate (g) Dietay fibe (g) Cholesteol Calcium Ion Thiamin Riboflavin Niacin Vitamin A Retinol Beta caotene vitamin C Vitamin E Unadjusted FFQ» vesus * Enegy adjusted.6 (.46-.7)t.6(.45-.7).5 (.-.6).55 (.9-.68).8(.9-.54).64 (.5-.75).57 (.4-.69).6 (.47-.7).7 (.6-.8).8 (.8-.45).6 (.6-.44).5 (.-.64).5 (.7-.66).(.-.48) -.56 (.4-.68).9 (.-.55).5 (.5-.65).56 (.4-.68), Unadjusted IDH* vesus Enegy adjusted.47(.-.6).45 (.8-.6).4(.5-.5).49 (.-.6).(.-.48).56 (.4-.68).7 (.59-.8).54 (.8-.67).67 ( ).45 (.7-.6). (.-.48).47 (.4-.6).49 (.-.6).4(.5-.5).5 (.4-.64).44 (.6-.59).5 (.4-.64).55 (.9-.68) Downloaded fom by guest on 6 Octobe 8 * FFQ, self-administeed food fequency questionnaie;, 7-day food ecod; IDH, inteviewed-administeed diet histoy. t Numbes in paentheses, 95% confidence inteval. Am J Epidemiol Vol. 4, No. 9, 996

6 958 Jain et al. TABLE 5. Peason's coelation coefficients () and intadass coelations ( { ) between two questionnaie methods and 7-day food ecods fo women (n 8), Toonto, Canada, Nutient Enegy (kcaj) Total fat (g) Satuated fat (g) Oleic acid (g) Linoleic acid (g) Potein (g) Cabohydate (g) Dietay fibe (g) Cholesteol Calcium Ion Thiamin Riboflavin Niacin Vitamin A Retinol Beta caotene Vitamin C Vitamin E Unadjusted FFQ' vesus 4 Enegy adjusted.44 (.8-.58)f.6 (.47-.7).4 (.6-.57).4 (.-.54).4 (.5-.57).45 (.8-.59).6(.47-.7).48(.-.6).67 ( ).55(.4-.67).44 (.7-.58).58 (.44-.7).5 (.4-.6).59 (.45-.7).8 (.-.5).58 ( ).6(.47-.7).5 (.8-.66) Unadjusted IDH* vesus Enegy adjusted. (.-.47).5 (.5-.6).4(.6-.5).9 (.-.54).54 (.9-.66).44 (.8-.58).68 ( ).4 (.5-.56).67 ( ).6(.46-.7).48 (.-.6).69 ( ).4 (.-.55).45 (.9-.59).7 (.9-.44).48(.-.6).57 (.4-.69).4 (.4-.55) FFQ, self-administeed food fequency questionnaie;, 7-day food ecod; IDH, inteviewed-administeed det histoy. t Numbes in paentheses, 95% confidence inteval mean coelation of.48 fo maconutients and.54 fo miconutients was obseved. Simila to men, the intaclass and unadjusted Peason coelations wee lowe. The Peason coelations fo enegy-adjusted nutients compaing the inteviewe-administeed diet histoy and the 7-day food ecod anged fom.7 to.69, with an aveage of.46 fo maco- and.49 fo miconutients. Compaisons wee also made between the two questionnaie methods and the 7-day food ecod based on categoizing nutient intakes into quatiles. Sepaate quatile cutpoints wee established fo each of the instuments fom thei espective distibutions of nutient intake by sex and sepaately fo enegy-adjusted and unadjusted nutients. In table 6, we examined the exact ageement pecentage within quatile categoies as measued by two instuments at a time. Fo these analyses, esults wee simila between enegy-unadjusted and enegy-adjusted intakes, and fo men and women, theefoe, esults ae pesented fo all subjects combined and fo enegy-adjusted nutient intakes only. The pecentage of exact ageement among quatiles anged fom to 48 fo enegy-adjusted nutients when compaing the 7-day food ecod and the food fequency questionnaie. The goss misclassification by extemes of quatiles anged fom to 5 pecent, ion, etinol, and thiamin contibuting most to the highe values of misclassification obseved. Simila values wee obseved when compaing the 7-day food ecod with the inteviewe-administeed diet histoy. Appoximately 9 pecent of the subjects wee classified within one categoy of quatiles by diffeent methods (data not shown). DISCUSSION Diet histoies o food fequency questionnaies have been the method of choice used in the geat majoity of epidemiologic studies of diet and chonic disease epoted to date in the past two decades. Geneally, thei use is based on consideations of logistics and feasibility. The inteviewe-administeed diet histoy method potentially offes seveal advantages as compaed with the self-administeed food fequency method. Fist, it is geneally possible to include moe food items on an inteviewe-administeed diet histoy, because the pesence of an inteviewe is moe likely to maintain a espondent's inteest. Second, the pesence of an inteviewe can help claify aeas of potential misundestanding by a espondent as compaed with eliance on witten instuctions that ae, of couse, necessay in the self-administeed situation. Thid, with an inteviewe-administeed diet histoy, quantification of amounts may geneally be moe detailed (e.g., the use of physical food models in the pesent study) as compaed with the food fequency Downloaded fom by guest on 6 Octobe 8 Am J Epidemiol Vol. 4, No. 9, 996

7 Compaison of Diet Assessment Methods 959 TABLE 6. Pecentage of ageement within quatiles between the two questionnaie methods and 7-day food ecods fo all subjects (n = ), Toonto, Canada, Nutient Enegy (kcal) Total fat (g) Satuated fat (g) Oloic acid (g) Undeic acid (g) Potein (g) Cabohydate (g) Dietay fibe (g) Cholesteol Calcium Ion Thiamin Riboflavin Niacin Vitamin A Retinol Beta caotene Vitamin C Vitamin E Exact ageement * vesus FFQ* Lowest on, highest on FFQ 4 4 Highest on, lowest on FFQ Exact ageement I vesus IDH' Lowest on, highest on IDH 4 Honest on, lowest on IDH *, 7-day food ecod; FFQ, self-administeed food fequency questionnaie; IDH, inteviewed-administged diet histoy. questionnaie whee quantification has to be elatively simple. These potential advantages suggest that the inteviewe-administeed diet histoy could estimate tue nutient intakes bette than the food fequency questionnaie. The pesent study has demonstated that the inteviewe-administeed diet histoy does not appea to be a bette pedicto than the food fequency questionnaie of nutients as estimated fom a 7-day food ecod. If anything, the food fequency questionnaie appeaed to esult in somewhat highe coelations oveall fo vaious nutients. The 7-day ecod, of couse, does not epesent a pefect "gold standad," but geneally, food ecods have been used as a standad fo many of the peviously epoted studies of the validity of vaious diet histoies (, ). Because of logistic easons, it was not possible in the pesent study to administe a second 7-day food ecod, which is consideed desiable to captue the seasonal and week-to-week vaiations (7, 8). Although this may have impacted on the absolute value of the coelations between the questionnaie methods and the food ecod method, it seems unlikely to have had any meaningful impact in tems of the elative coelation between the questionnaies and the food ecods. The two questionnaie methods used in the pesent study ae quite compaable with those that have been used in a numbe of epidemiologic studies (, 7, 9). The study by Block et al. (), conducted on 85 subjects aged 5-5 yeas, epoted that the self-administeed food fequency questionnaie coelated moe highly with food ecods than did the patially self- and patially inteviewe-administeed one used in thei study. It seems easonable, theefoe, to infe that, in geneal, inteviewe-administeed diet histoies do not offe any paticula advantage as compaed with the self-administeed food fequency method in tems of the validity of estimated nutient intakes, when the validity assessment is based on food ecods as standads. A specific example of the application of this conclusion is to epidemiologic studies of fat intake and beast cance isk. In geneal, case-contol studies of this postulated association, pimaily based on inteviewe-administeed diet histoies, have been positive, wheeas cohot studies based on self-administeed food fequency methods have been much less positive o null (, ). If the self-administeed food fequency methods wee appeciably pooe estimatos of nutient intake than inteviewe-administeed diet histoies, measuement eo fo the cohot studies would be coespondingly geate than that fo case-contol studies, and hence the cohot studies could be subject to geate attenuation of the obseved isk. The pesent study suggests that this is not a tenable explanation fo the discepancy between the case-contol and cohot studies and that altenative explanations, fo example, in tems of selection bias, might be moe elevant (). The key advantage of the self-administeed food fe- 4 Downloaded fom by guest on 6 Octobe 8 Am J Epidemiol Vol. 4, No. 9, 996

8 96 Jain et aj. quency questionnaie is the feasibility of applying it to lage numbes of individuals as in dietay cohot studies. The pesent esults suggest that the validity of such studies is not theatened by the use of a selfadministeed food fequency questionnaie as compaed with an inteviewe-administeed diet histoy to estimate nutient intake. Possible exceptions to this may be populations whee the fomal education level is low and whee people ae unfamilia with sefadministeed questionnaies. ACKNOWLEDGMENTS The authos thank Andew White fo pocessing the data fo the study. REFERENCES. Gibson R. Pinciples of nutitional assessment New Yok: Oxfod Univesity Pess, 99.. Willett W. Nutitional epidemiology. New Yok: Oxfod Univesity Pess, 99.. Block G, Thompson FE, Hatman AM, et al. Compaison of two dietay questionnaies validated against multiple dietay ecods collected duing a -yea peiod. J Am Diet Assoc 99;9: Jain M, Howe GR, Johnson KC, et al. Evaluation of a diet histoy questionnaie fo epidemiologic studies. Am J Epidemiol 98;l : Jain M. Diet histoy: questionnaie and inteview techniques used in some etospective studies. J Am Diet Assoc 989;89: Watt BK, Meill AL. Composition of foods: aw, pocessed, pepaed. Washington, DC: Agicultue Reseach Sevice, US Depatment of Agicultue, 96, expansion Mach 97. (USDA handbook no. 8). 7. Rimm EB, Giovannucci EL, Stampfe MJ, et al. Repoducibility and validity of an expanded self-administeed semiquantitative food fequency questionnaie among male health pofessionals. Am J Epidemiol 99;5: Willett WC, Sampson L, Stampfe MJ, et al. Repoducibility and validity of a semiquantitative food fequency questionnaie. Am J Epidemiol 985;: Hankin JH, Wilkens LR, Kolonel LN, et al. Validation of a quantitative diet histoy method in Hawaii. Am J Epidemiol 99;: Howe GR. Dietay fat and beast cance two views. Pesented at the Confeence on Beast Cance Reseach: Cuent Issues- Futue Diections, Atlanta, Geogia, Apil 7, 99.. Willett WC. Dietay fat and beast cance two views. Pesented at the Confeence on Beast Cance Reseach: Cuent Issues-Futue Diections, Atlanta, Geogia, Apil 7, 99. Downloaded fom by guest on 6 Octobe 8 Am J Epidemiol Vol. 4, No. 9, 996