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BRIEF ABSTRACT
Journal Name: Cancer Causes Control (2008) 19:595–603
Title: Dietary assessment in the California Teachers Study:
reproducibility and validity
Authors: Horn-Ross PL, Lee VS, Collins C, Stewart SL, Canchola AJ, Lee MM, Reynolds P,
Clarke CA, Bernstein L, Stram DO. contact: Pamela.Horn-Ross@nccc.org
Abstract:
Objective: To evaluate the reproducibility and validity of
the food-frequency questionnaire (FFQ) used in the California
Teachers Study (CTS) cohort and to use this data to
quantify the effects of correcting nutrient-breast cancer
relative risks for measurement error.
Methods: One hundred and ninety five CTS cohort members
participated in a 10-month dietary validation study that
included four 24-h dietary recalls and pre- and post-study
FFQs. Shrout–Fleiss intraclass correlations for reproducibility
were computed. Under several standard assumptions
concerning the correlations of errors in the FFQs and 24-h
recalls, we calculated energy-adjusted deattenuated Pearson
correlations for validity and tested for differences in validity
according to a number of demographic and other risk factors.
For each nutrient, we compared the performance of the
FFQ versus the 24-h recalls, estimating the number of days
of recalls that give equivalent information about true intake
as does a single FFQ. Finally, the effects of adjustment for
measurement error on risk estimates were evaluated in
44,423 postmenopausal cohort members, 1,544 of whom
developed breast cancer during seven years of follow-up.
Relative risks (RR) and confidence intervals (CI) were
calculated using Cox proportional hazards with and without
correction for measurement error.
Results: Reproducibility correlations for the nutrients
ranged from 0.60 to 0.87. With a few exceptions, validity
correlations were reasonably high (range: 0.55–0.85),
including r = 0.74 for alcohol. Performance of the FFQ
differed by age for percent of calories from fat and by body
mass index and hormone therapy use for alcohol consumption.
For most nutrients examined, our FFQ is
comparable to two to six recalls for each subject in capturing
true intake. In the measurement error-adjusted risk
analyses, corrected RRs were within 13% of uncorrected
values for all nutrients examined except for linoleic acid.
For alcohol consumption the corrected RR (per 20 g/
1,000 kcal/d) was 1.36 (95% CI: 1.03–1.51) compared to
the uncorrected estimate of 1.25 (95% CI: 1.10–1.42).
Conclusion: The FFQ dietary assessment used in the CTS
is reproducible and valid for all nutrients except the
unsaturated fatty acids. Correcting relative risk estimates
for measurement error resulted in relatively small changes
in the associations between the majority of nutrients and
the risk of postmenopausal breast cancer.
For more information via the journal's Website CLICK HERE.
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