Dataset Information

Test-retest reproducibility of a food frequency questionnaire (FFQ) and estimated effects on disease risk in the Norwegian Women and Cancer Study (NOWAC).

ABSTRACT:

Background

The Norwegian Women and Cancer Study (NOWAC) is a national population-based cohort study with 102 443 women enrolled at age 30-70 y from 1991 to 1997. The present study was a methodological sub-study to assess the test-retest reproducibility of the NOWAC food frequency questionnaire (FFQ), and to study how measurement errors in the data can affect estimates of disease risk.

Methods

A random sample of 2000 women aged 46-75 y was drawn from the cohort in 2002. A self-instructive health and lifestyle questionnaire with a FFQ section was mailed to the same subjects twice (test-retest), about three months apart, with a response rate of 75%. The FFQ was designed to assess habitual diet over the past year. We assess the reproducibility of single questions, food groups, energy, and nutrients with several statistical measures. We also demonstrate the method of regression calibration to correct disease risk estimates for measurement error. Alcohol intake (g/day) and high blood pressure (yes/no) is used in the example.

Results

For single foods there were some indications of seasonal reporting bias. For food groups and nutrients the reliability coefficients ranged from 0.5-0.8, and Pearson's r, Spearman's rs, and two intraclass correlation coefficients gave similar results. Although alcohol intake had relatively high reproducibility (r = 0.72), odds ratio estimates for the association with blood pressure were attenuated towards the null value compared to estimates corrected by regression calibration.

Conclusion

The level of reproducibility observed for the FFQ used in the NOWAC study is within the range reported for similar instruments, but may attenuate estimates of disease risk.

SUBMITTER: Parr CL

PROVIDER: S-EPMC1434764 | biostudies-literature | 2006 Jan

REPOSITORIES: biostudies-literature

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Publications

Test-retest reproducibility of a food frequency questionnaire (FFQ) and estimated effects on disease risk in the Norwegian Women and Cancer Study (NOWAC).

Parr Christine L CL Veierød Marit B MB Laake Petter P Lund Eiliv E Hjartåker Anette A

Nutrition journal 20060131

<h4>Background</h4>The Norwegian Women and Cancer Study (NOWAC) is a national population-based cohort study with 102 443 women enrolled at age 30-70 y from 1991 to 1997. The present study was a methodological sub-study to assess the test-retest reproducibility of the NOWAC food frequency questionnaire (FFQ), and to study how measurement errors in the data can affect estimates of disease risk.<h4>Methods</h4>A random sample of 2000 women aged 46-75 y was drawn from the cohort in 2002. A self-inst ...[more]

PMID: 16448553

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Project description:The food frequency questionnaires (FFQs) are the most common tools used in dietary research. Each newly developed, modified, or adapted FFQ should be validated in the target population. The aim of this study was to assess the reproducibility and relative validity of the 72-item semi-quantitative food frequency questionnaire (72-item SQ-FFQ) for Polish adults. The 72-item SQ-FFQ was developed based on a non-quantitative FFQ covering 62 food items (62-item FFQ-6®). The study was conducted among 186 university students aged 19-26 years (47.8% of females). The FFQ was administered on two occasions (FFQcrude and FFQretest) to assess the test-retest reproducibility, and the FFQcrude was compared with the estimated food record (FRcrude) to evaluate the relative validity of the FFQ in assessing the intake of energy, 38 nutrients, and alcohol. The energy intake obtained with both methods was standardized to 2000 kcal/day (FFQstand, FRstand). The dietary intake obtained with FFQcrude was adjusted using linear regression analysis (FFQreg). The reproducibility and relative validity of the FFQ were assessed by comparing the mean values of energy and nutrient intake and using Spearman's correlation coefficient, the cross-classification analysis, and the Bland-Altman method. Spearman's correlation coefficient between both administrations of the FFQ ranged from 0.631 to 0.878 (the intraclass correlation coefficient: 0.583-0.935), for FFQcrude and FRcrude ranged from -0.025 to 0.390, for FFQstand and FRstand ranged from 0.021 to 0.546, and for FFQreg and FRcrude ranged from 0.028 to 0.391. The percentage of respondents classified into the same or adjacent quartiles of nutrient intake obtained from two administrations of the FFQ ranged from 84.9% to 97.8%, for FFQcrude and FRcrude ranged from 61.3% to 76.9%, for FFQstand and FRstand ranged from 63.4% to 83.9%, and for FFQreg and FRcrude ranged from 60.2% to 76.9%. In conclusion, our findings showed good reproducibility and acceptable relative validity of the 72-item SQ-FFQ. This tool can be recommended for assessing dietary intake among Polish young adults. However, the intake of certain nutrients should be interpreted with caution.

Project description:BackgroundIodized salt is not mandatory in Norway, and the permitted level of iodine in table salt is low (5 μg/g). Thus, milk and dairy products, fish and eggs are the main dietary sources of iodine in Norway. Mild-to-moderate iodine deficiency in pregnant women has been described in several European countries, including Norway. There are few validated tools available to assess iodine intake in an efficient manner. The aim of the current study was to assess the validity and reproducibility of a new iodine-specific food frequency questionnaire (I-FFQ) in Norwegian pregnant women.MethodsAn I-FFQ consisting of a total of 60 food items and the use of supplements was developed to assess iodine intake and was administrated to 137 pregnant women at gestational week 18-19. Reference methods were a structured 6-days iodine specific food diary, urinary iodine concentration (UIC) (pooled sample of spot UIC from six consecutive days), and thyroid function tests. Correlation analyses, Cohen's weighted kappa, Bland-Altman plots, and linear regression analyses were used to assess validity. Reproducibility of the I-FFQ was assessed in a subgroup (n = 47) at gestational week 35-36.ResultsThere was a strong correlation between estimated iodine intake from the I-FFQ and food diary (r = 0.62, P < 0.001) and an acceptable correlation between the I-FFQ and UIC (r = 0.21, P = 0.018). There was no significant association between the I-FFQ and thyroid function tests. The I-FFQ estimated higher iodine intake compared to the food diary with a mean absolute difference 33 μg/day. The limits of agreement from the Bland-Altman plots were large, however few participants fell outside the limits of agreement (5.2-6.5%). There was no difference between the estimated iodine intake from the I-FFQ assessed at gestational week 18-19, and gestational week 35-36 (P = 0.866), and there was a strong correlation between the two time points (r = 0.63, P < 0.001).ConclusionIn summary, this study suggests that the I-FFQ can be used as a valid tool to estimate and rank iodine intake among Norwegian pregnant women. We further suggest that this I-FFQ may also be valid in other populations with similarly dietary patterns and where salt is not iodized.Trial registrationThe study is registered in ClinicalTrials.gov (NCT02610959).

Project description:The aim of this study was to evaluate the test-retest reproducibility of a non-quantitative food frequency questionnaire (acronym: 62-item FFQ-6) and the possibility of identifying dietary patterns (DPs) in 13-21-year-old females. The study involved 97 females within three age groups: 13-15, 16-18, and 19-21 years, including 31, 38, and 28 subjects, respectively. The questionnaire was completed twice with a two-week interval (test and retest). For the total sample, using a principal component analysis (PCA), two similar PCA-driven DPs (DP1 and DP2) were identified separately from test data and retest data, considering two sets of input variables. 60-item-DP1 and 60-item-DP2 were identified after excluding two items-vegetables and fruits in general-due to including single items of various kinds of vegetables and fruits. After an aggregation of some items of the questionnaire, 25-item-DP1 and 25-item-DP2 were identified. The kappa statistic (test vs. retest) in the total sample averaged at 0.52 (0.32-0.72 for food items), while within age groups, it averaged at 0.41, 0.53, and 0.65, respectively. The percentage of subjects classified into the same food frequency category (test vs. retest) in the total sample averaged at 68% (51%-89% for food items), while within age groups, it averaged at 60%, 68%, and 77%, respectively. The Spearman correlations between dietary pattern scores (test vs. retest) in the total sample were: 0.84 (within age groups 0.83, 0.81, and 0.78, respectively) for 60-item-DP1, 0.68 (within age groups 0.24, 0.79, and 0.76, respectively) for 60-item-DP2, 0.76 (within age groups 0.56, 0.82, and 0.89, respectively) for 25-item-DP1, and 0.48 (within age groups 0.40, 0.57, and 0.53, respectively) for 25-item-DP2 (p < 0.05 for all). In conclusion, the test-retest reproducibility of the 62-item FFQ-6 was good or very good for most food items, with a tendency to be higher in older age groups of females under study. Due to the acceptable-to-good reproducibility of dietary pattern identification, the use of a 62-item FFQ-6 to describe the overall diet of young Polish females can be recommended.

Project description:BackgroundStatistical methods to model the usual dietary intake of foods in a population generally ignore the additional information on the never-consumers. The objective of this study is to determine the added value of Food Frequency Questionnaire (FFQ) data allowing distinguishing the never-consumers from the non-consumers while modeling the usual intake distribution.MethodsThree food items with a different proportion of never-consumers were selected from the database of the Belgian food consumption survey of 2004 (N = 3200). The usual intake distribution for these food items was modeled with the Statistical Program for Analysis of Dietary Exposure (SPADE) and modeling parameters were extracted. These parameters were used to simulate (a) a new database with two 24-h recalls per respondent and (b) a "true" usual intake distribution. The usual intake distribution from the new database was obtained by modeling the 24-h recalls with SPADE, once without and once with the inclusion of the FFQ data on the never-consumers. Ratios were calculated for the different percentiles of the usual intake distribution: the modeled usual intake (g/day) (for both SPADE with and without the inclusion of FFQ data on never-consumers) was divided by the corresponding percentile of the simulated "true" usual intake (g/day). The closer the ratio is to one, the better the model fits the data.ResultsInclusion of the FFQ information to identify the never-consumers did not improve the estimation of the higher percentiles of the usual intake distribution. However, taking into account this FFQ information improved the estimation of the lower percentiles of the usual intake distribution even when the proportion of never-consumers was low.ConclusionsThe inclusion of FFQ information to identify the never-consumers is beneficial when interested in the whole usual intake distribution or in the lower percentiles only, no matter how low the proportion of never-consumers for that food item may be. However, when interest is only in the higher percentiles of the usual intake distribution, inclusion of FFQ information to identify the never-consumers will have no benefit.

Dataset Information

Test-retest reproducibility of a food frequency questionnaire (FFQ) and estimated effects on disease risk in the Norwegian Women and Cancer Study (NOWAC).

Background

Methods

Results

Conclusion

Publications

Test-retest reproducibility of a food frequency questionnaire (FFQ) and estimated effects on disease risk in the Norwegian Women and Cancer Study (NOWAC).

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