Discussion
CROSS
To explore the perceived portion size norm of discretionary foods in Australian adults, an image-based tool for 15 common discretionary foods was developed and validated against corresponding real foods. Agreement between the methods was found to be high based on cross-classification analysis and ICC. Cross classification showed over 90% of selections were matched to the same or adjacent portion size option out of a series of eight options. Similarly, ICC results demonstrated good to excellent agreements for most foods, although three foods had moderate agreement. Cooking confidence was positively associated with level of agreement; participants who reported higher cooking confidence tended to achieve higher percentage of correct matches across foods.These findings are consistent with other validation studies using a series of food images, with the proportion of correct and adjacent matches varying between 80–98% across studies [The displayed portion size options were carefully considered in the current study. A wide range of options were displayed to minimise potential social desirability bias and these options were pilot tested in the target population to ensure feasibility [Despite the overall good level of agreement, the images-series for a few foods including banana bread, muffin, and chocolate bar showed only moderate ICCs. For banana bread and muffin, one study noted similar results that the image-series for bread slice performed poorly [Several strengths of the methodology used to validate this newly developed tool can be noted. This online image-based tool has a low respondent burden as it is easily accessible with any electronic device [