Reliability and validity of digital imaging as a measure of schoolchildren's fruit and vegetable consumption

As more and more interventions aim to increase schoolchildren's fruit and vegetable (FV) consumption, less resource-intensive yet valid alternatives to weighed plate waste (WPW) are needed for assessing dietary intake.

We aimed to test the reliability and validity of digital imaging (DI) and digital imaging with observation (DI+O) in assessing children's FV consumption during school lunch.

FV consumption (in grams) was assessed on lunch trays from third- to fifth-grade children over eight visits (31 to 68 trays collected per visit) to compare WPW with DI and DI+O.

Two elementary schools (327 and 631 students enrolled, respectively).

Interobserver reliability of DI. Validity of DI and DI+O compared against WPW.

Reliability was assessed by percent agreement and intraclass correlation coefficients (ICCs). Validity was assessed by Pearson correlations, paired t tests, and Bland-Altman plots.

Reliability was acceptable for DI; percent agreement was 96% and the ICC was 0.92. FV consumption assessments by DI and WPW (n=159) were highly correlated (r=0.96; P<0.001). Mean FV consumption using DI (96.7 g) was within 1.0 g of WPW and not significantly different from WPW (P=0.56), and Bland-Altman limits of agreement for individual-tray FV consumption were -32.9 to 31.3 g. FV consumption assessments by DI+O and WPW were highly correlated (r=0.98; P<0.001). Mean FV consumption using DI+O (99.3 g) was within 1.0 g of WPW and not significantly different from WPW (P=0.38), and limits of agreement for individual-tray FV consumption were -25.0 to 26.8 g.

DI was reliable for assessing children's FV consumption during school lunch. DI and DI+O were valid for assessing mean consumption but less precise for estimating individual-tray consumption. Valid estimations of mean FV consumption were achieved using DI without cafeteria observations, thereby reducing labor and time. Thus, DI is especially promising for assessing children's mean FV consumption during school lunch.