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. 2018 Aug;118(8):1482-1489.
doi: 10.1016/j.jand.2018.02.002. Epub 2018 Apr 12.

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

Melanie K Bean, Hollie A Raynor, Laura M Thornton, Alexandra Sova, Mary Dunne Stewart, Suzanne E Mazzeo

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

Melanie K Bean et al. J Acad Nutr Diet. 2018 Aug.

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.

Keywords: Elementary school; Nutrition policy; Plate waste; Salad bars; School lunch.

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Conflict of interest statement

Conflicts of interest: none to report

Figures

Figure 1
Figure 1
Column 1 presents samples of three reference portions of spinach in: a) ¼ cup; b) ½ cup; c) ¾ cup portions. Column 2 provides a sample mock salad at: d) pre-consumption; e) post-consumption without dressing; and f) post-consumption with salad dressing. Mock salads and reference portions were created for use in a simulated laboratory-based study to establish the reliability and validity of digital imagery for determining starting portion size and waste from elementary school self-serve salad bars.
Figure 2
Figure 2
Bland-Altman plots comparing digital imagery-estimated measurements with measured weights of A) starting portions and B) plate waste of vegetables from salad bars in a simulated laboratory-based study. The difference between methods was plotted as weighed method minus digital imagery estimation method. The center line represents the mean difference between weighed and digital imagery methods. The upper and lower boundaries represent the 95% limits of agreement between methods.
See this image and copyright information in PMC

References

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