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Original Research: Brief
Reliability and Validity of Digital Imagery Methodology for Measuring Starting Portions and Plate Waste from School Salad Bars

https://doi.org/10.1016/j.jand.2018.02.002Get rights and content

Abstract

Background

Scientifically sound methods for investigating dietary consumption patterns from self-serve salad bars are needed to inform school policies and programs.

Objective

To examine the reliability and validity of digital imagery for determining starting portions and plate waste of self-serve salad bar vegetables (which have variable starting portions) compared with manual weights.

Design/methods

In a laboratory setting, 30 mock salads with 73 vegetables were made, and consumption was simulated. Each component (initial and removed portion) was weighed; photographs of weighed reference portions and pre- and post-consumption mock salads were taken. Seven trained independent raters visually assessed images to estimate starting portions to the nearest ¼ cup and percentage consumed in 20% increments. These values were converted to grams for comparison with weighed values.

Statistical analyses

Intraclass correlations between weighed and digital imagery–assessed portions and plate waste were used to assess interrater reliability and validity. Pearson’s correlations between weights and digital imagery assessments were also examined. Paired samples t tests were used to evaluate mean differences (in grams) between digital imagery–assessed portions and measured weights.

Results

Interrater reliabilities were excellent for starting portions and plate waste with digital imagery. For accuracy, intraclass correlations were moderate, with lower accuracy for determining starting portions of leafy greens compared with other vegetables. However, accuracy of digital imagery–assessed plate waste was excellent. Digital imagery assessments were not significantly different from measured weights for estimating overall vegetable starting portions or waste; however, digital imagery assessments slightly underestimated starting portions (by 3.5 g) and waste (by 2.1 g) of leafy greens.

Conclusions

This investigation provides preliminary support for use of digital imagery in estimating starting portions and plate waste from school salad bars. Results might inform methods used in empirical investigations of dietary intake in schools with self-serve salad bars.

Section snippets

Methods

This study was conducted by trained research staff at Virginia Commonwealth University in preparation for a larger investigation of the impact of school salad bars on dietary consumption patterns among Title I elementary school students. The current validation study was conducted in the laboratory setting and did not involve human subjects; thus it was not subject to institutional review board approval.

Results

IRRs were 0.91 for determining starting portions of vegetables and 0.99 for determining percentage plate waste among the seven raters, indicating excellent agreement. When examined by category, ICCs for determining starting portion estimates were lower for other vegetables (0.89) compared with leafy greens (0.92), yet both demonstrated excellent rater agreement. IRRs for determining plate waste were excellent for both leafy greens (0.99) and other vegetables (0.99; Table 1). IRRs for plate

Discussion

The main findings from this study were that digital imagery was both reliable and valid for estimating consumption (starting portion and waste) of salad bar vegetables and did not differ significantly from weighed methods overall. IRRs when digital imagery was used were excellent for determining consumption and comparable to those reported previously with other foods.7, 9 Although digital imagery has been used with salad bars in a handful of prior investigations,9, 21 this study is the first to

Conclusions

This investigation builds on prior digital imagery validation studies by specifically investigating use of digital imagery for assessment of variable starting portions of vegetables from self-serve salad bars and use of a weighed reference portion and statistical approach with a measure of agreement (ICC).20 Results suggest that use of digital imagery with photographs of measured reference portions to aid in assessment of starting portions might be a reliable and valid method for estimation of

Acknowledgements

The authors would like to thank April Williams, MS, LDN, for her assistance with this study.

Author Contributions

M. K. Bean designed the study, conducted data collection and analyses, and drafted the manuscript; H. A. Raynor contributed to study design and methods; L. M. Thornton informed study analyses and interpretation of results; A. Sova collected the data and oversaw data management; M. Dunne Stewart coordinated school salad bar information with Eat Fresh RPS; S. E. Mazzeo contributed to study design and

M. K. Bean is an associate professor, Department of Pediatrics, Children’s Hospital of Richmond at Virginia Commonwealth University, Richmond.

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  • Cited by (11)

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      This study was approved by [Virginia Commonwealth University's] Institutional Review Board. Validated digital imagery plate waste methods were implemented (Taylor et al., 2014; Bean et al., 2018). Each school pair was rated once, with pairs rated on the same day to match menu and day.

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      Weights were obtained using a calibrated food scale (Ozeri Pronto Digital Food Scale [Model ZK14-S; Ozeri Kitchen]), and the average was used as the reference weight for one portion of that item. For self-serve fruits and vegetables, reference portions (1/4 cup, 1/2 cup, 3/4 cup, and 1 cup) were prepared in triplicate, weighed, averaged, and photographed by lab dietitians as described elsewhere (Bean et al., 2018). Product information on each food and beverage was provided by the school district dietitian and entered into Nutrition Data Systems for Research (Nutrition Data Systems for Research, 2018) to obtain nutrient information.

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    M. K. Bean is an associate professor, Department of Pediatrics, Children’s Hospital of Richmond at Virginia Commonwealth University, Richmond.

    A. Sova is a research assistant, Department of Pediatrics, Children’s Hospital of Richmond at Virginia Commonwealth University, Richmond.

    H. A. Raynor is a professor, Department of Nutrition, University of Tennessee, Knoxville.

    L. M. Thornton is an associate research professor, Department of Psychiatry, University of North Carolina, Chapel Hill.

    M. Dunne Stewart is CEO, Greater Richmond Fit4Kids, Richmond, Virginia.

    S. E. Mazzeo is a professor, Department of Psychology, Virginia Commonwealth University, Richmond.

    STATEMENT OF POTENTIAL CONFLICT OF INTEREST No potential conflict of interest was reported by the authors.

    FUNDING/SUPPORT This work was supported in part by Impact 100 to Greater Richmond Fit4Kids (PI: Mary Dunne Stewart) and NICHD 1R03HD088985-01 to Virginia Commonwealth University (PI: Melanie K. Bean).

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