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Surrogate Sources of Dietary Information . Nutritional epidemiology WALTER WILLETT. Introduction. Surrogate sources of information on diet are needed for investigating diseases that are immediately or rapidly fatal—ex. Lung cancer, stomach cancer. Index subject---
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Surrogate Sources of Dietary Information Nutritional epidemiology WALTER WILLETT
Introduction • Surrogate sources of information on diet are needed for investigating diseases that are immediately or rapidly fatal—ex. Lung cancer, stomach cancer. Index subject--- 1. may be deceased or too ill 2. currently may alter dietary pattern 3. may be in poor cognitive level — too young or too old
Exclusion of subjects who cannot provide dietary information directly —if diets affect prognosis, bias may result ex. beta-carotene and small cell lung cancer malnutrition and cognitive impairment —may lengthen the duration of a study — may be impracticable for some diseases such as fatal myocardial infarction
a surrogate measure----dietary information may be obtained from spouse, sibling, child, or other information, or using spouse’s diet, or biochemical measurements from a healthy spouse --measurement error (but may be less biased) --random misclassification might be increased --differential misclassification might be reduced—has not been evaluated
Chapter Contents literature review on surrogate sources of dietary information, including: • The availability of dietary information from surrogates • The validity of such information • The implications of using surrogates on study design and data analysis
Availability of information from surrogate respondents • Pickle and colleagues (1983)-cigarette smoking early life—siblings adult life—spouses and children • Nelson and colleagues (1994) -cigarette smoking and alcohol drinking—the degree of nonresponse the completeness of the data--- 1. Spouses 2. first degree relatives 3. friends or others • Rocca et al. (1986) -cigarette smoking and alcohol drinking 60%--spouses, 40% first degree relatives
Availability of information from surrogate respondents • Samet et al. (1985) -cigarette smoking The next of kin of those who had died 2 to 6 years earlier • Samet et al. (1985) –vitamine A and its carotenoid precursors and lung cancer The (Table 8-1)
Comparability of information from surrogate respondents • Kolonel and coworkers (1977) (Table 8-2): --The level of agreement between the two interviews varied with the frequently consumed foods --The extent of agreement for the foods was comparable with that for age started to smoke and for the number of cigarettes smoked.
Marshall et al(1980) (Table 8-3) • Humble et al (1984) (Table 8-4,8-5) agreement of index subject-based and spouse-based indices of total consumption—spearman rank order correlation and by comparison of quantile groupings • Metzner et al(1989) (Table8-6) • Herrmann (1985) (Table8-7) • Lerchen and Samet (1986) • Hislop et al (1992) • --food frequescy questionnaire • Moore et al (1970)--7-day food record
Using surrogate reports on food consumption --for studies that aim to compare group means—cross-cultural or international comparisons • The extent of agreement depends on the frequency with which a food is consumed, the sex of the index subject, the relationship of the surrogate to the index subject, and the method of data collection.
Use of spouse diet as a surrogate • Assumption: Married couples share similar diets for a long period of time. Nomura et al.(1978) Jensen et al.(1980) • The correlation of husbands and wives diets Kolonel and Lee(1981,1982) --the diet of a spouse may serve as a surrogate when another source of information is unavailable. further methodologic interest:Comparisons of associations estimated from a typical case-control study in which subjects themselves are interviewed with those from interviews of spouses of the same cases and controls.
Parents as surrogates for children • Dietary patterns adopted early in life may influence the risk of chronic disease in later years.—assessing the diets of young children • Uncertain quality—children’s unfamilar with food names, the ability to recall details from the past, not accurate sense of time , shot attention spans—using parents as surrogate reporters of their children’s diet.
(Table 8-8)—independent comparison data to validate surrogate reports of the children’s diet by parents. --shows random but non-trivial differences between reports of mothers and those of trained observers. • (Fig 8-1)—differences between the two sources were larger and tended to be in the direction of overreporting by the mother. • (Fig 8-2)—the correlations between mothers’ and objective observer’s reports
Whether the accuracy of surrogate information differs between mothers and fathers---(Table 8-9)—surrrogate: the one who had primary responsibility for food preparation. • (Table 8-10)—mothers may report what children ate during meals much better than what children ate during between-meal snacks. • Parents appear to be able to give a moderately valid indication of what their children ate in the previous 24 hours. Factors that lesson the time parents spend with the index child, such as employment outside of the home, larger family size—less accurate.
Study design and data analysis • The potential for bias appears to be greatest when data for one group, such as cases, are obained from surrogates, whereas data for another, such as controls, are obtained from the index subjects. • The direction of information bias has not been documented. • Wilkens et al. (1992)–differential misclassification appears not to have been a major problem.
Study design and data analysis • Even if unbiased mean values for cases and controlsare provided by surrogate sources, random misclassification in estimate of individual intake mayy bias neasures of association toward null values.(Lyon et al.,1992) • Sample size must be inflated. (Nelson et al.,1992)—more cases, more missing expected from surrogate,nondofferential missclassification of exposure status diminishes the statistical power.
Analytic stratigies for using data from surrogate respondents: • 1.the extent of missing data for the various respondent groups should be assessed and a determination made concerning the extent of missing information that is acceptable. • To stratify by respondent type to asses its potential role as a confounding or modifying variable. • Not to pool the study data.
Conclusions • Reliance on surrogate sources of information may be unavoidable in investigating illness that are rapidly fatal or impair cognition significantly.(2% of the medline abstract) • Proxy information concerning diet may introduce measurement error in analytical investigations of dietary hypothesis. • The measurement error may be random or may be differential with respect to respondent type. • For dietary hypothesis, where the effects of interest are often either unknown or anticipated to be relatively small. • Use of surrogate sources of dietary information should be minimized in studies of diet and disease.
