mean the same thing for all individuals, even if the item is worded the same way or has been harmonized to have an equivalent metric. Study DIF could arise due to differences in the harmonized items or simply due to differences in how the sampled populations interpreted and responded to items.3 Figure 2 highlights that one item, “over tired”, shows an atypical developmental trend relative to other items and exclusively in the AFDP study. Given this aberrant pattern, we removed the item from further consideration.
