Research ArticleManaging Outliers in Adolescent Food Frequency Questionnaire Data
Section snippets
INTRODUCTION
Childhood obesity is a serious public health problem in the US. The National Health and Nutrition Examination Survey indicates a steady increase in the prevalence of childhood overweight and obesity over the past 2 decades.1 Multiple interventions have been developed in response to this alarming trend. Studies evaluating the effects of these interventions have used a variety of different measures to assess key variables—primarily food intake.
The assessment of food intake has emerged as a major
METHODS
The present study was a secondary analysis of data from a broader behavioral intervention study to promote weight loss among African American adolescents with primary obesity. Full details of the trial methodology and enrollment/recruitment are reported elsewhere.17 In brief, the parent study was the Sequential Multiple Assignment Randomized Trial18 to develop an adaptive intervention for adolescent weight loss. Adolescents were first randomized to either home- or office-based weight-loss
RESULTS
Participants were 181 African American adolescents (Table 2). Summaries of energy intake at both baseline and follow-up, including outliers and under the 5 decision rules, are presented in Table 3. Compared with no removal of outliers, the number of cases removed ranged from 7 (3.9%) to 22 (12.2%) at baseline and 5 (3.2%) to 23 (14.6%) at follow-up. As expected, in all instances, the SD was reduced, and the range of values narrowed when outlier decision rules were applied (compared with no
DISCUSSION
Guidance for identifying outliers and the effect of outlier removal in child and adolescent FFQ data has received little attention in the literature. In this study, the application of outlier decision rules culled from the extant literature on outliers in adult FFQ data had notable effects (compared with no removal of outliers) on the results and the conclusions drawn from an adolescent sample. The use of outlier decision rules altered the number of cases available for analysis but also change
IMPLICATIONS FOR RESEARCH AND PRACTICE
This study suggests a process for the identification and removal of outliers. These results suggest that investigators examine different decision rules to understand how the removal of outliers affects study findings. Currently, there is insufficient information to suggest a single optimal outlier removal strategy. More research is needed to understand how the removal of dietary intake outliers affect weight and psychosocial outcomes. In the meantime, a good strategy is to carefully evaluate
ACKNOWLEDGMENTS
This work was supported by the National Heart, Lung, and Blood Institute and the Eunice Kennedy Shriver National Institute of Child Health and Human Development (grant no. U01HL097889; ClinicalTrials.gov Identifier no. NCT01350531. The National Institutes of Health had no role in the study design; data collection, analysis, or interpretation; writing of this manuscript; or the decision to submit the manuscript.
REFERENCES (38)
- et al.
Relative reliability and validity of the Block Kids Questionnaire among youth aged 10 to 17 years
J Am Diet Assoc
(2008) - et al.
How children remember what they have eaten
J Am Diet Assoc
(1994) - et al.
Recency affects reporting accuracy of children's dietary recalls
Ann Epidemiol
(2004) - et al.
Number of days of food intake records required to estimate individual and group nutrient intakes with defined confidence
J Nutr
(1987) - et al.
Relative validity of the Iowa Fluoride Study targeted nutrient semi-quantitative questionnaire and the block kids’ food questionnaire for estimating beverage, calcium, and vitamin D intakes by children
J Am Diet Assoc
(2008) - et al.
Overweight children find food more reinforcing and consume more energy than do nonoverweight children
Am J Clin Nutr
(2008) - et al.
Development of food intake patterns for the MyPyramid food guidance system
J Nutr Educ Behav
(2006) - et al.
A randomized pilot study of multisystemic therapy targeting obesity in African-American adolescents
J Adolesc Health
(2009) - et al.
Preliminary validation of the Yale food addiction scale
Appetite
(2009) - et al.
Comorbidity between depression and disordered eating in adolescents
Eat Behav
(2007)
African-American adolescents’ weight loss skills utilization: effects on weight change in a sequential multiple assignment randomized trial
J Adolesc Health
A questionnaire approach to measuring the relative reinforcing efficacy of snack foods
Eat Behav
Brief report: a randomized controlled trial examining peer support and behavioral weight loss treatment
J Adolesc
Prevalence of obesity and severe obesity in US children, 1999-2016
Pediatrics
Issues in dietary intake assessment of children and adolescents
Br J Nutr
Measurement issues related to studies of childhood obesity: assessment of body composition, body fat distribution, physical activity, and food intake
Pediatrics
Structure of dietary measurement error: results of the OPEN biomarker study
Am J Epidemiol
Reproducibility and validity of an expanded self-administered semiquantitative food frequency questionnaire among male health professionals
Am J Epidemiol
Comparative validation of the Block, Willett, and National Cancer Institute food frequency questionnaires: the Eating at America's Table Study
Am J Epidemiol
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Conflict of Interest Disclosure: The authors have not stated any conflicts of interest.