Where some but not all items display such DIF, it is possible to treat them as a different item in each country.
Of the 160 items included in the item bank, one was removed because it was worded differently in two different item sets.
Because most of our target misconceptions appeared in more than one item (between 1 and 5 items), for each student, we totaled the number of distractors they selected that included a given misconception and standardized the counts by dividing by the total possible selections (e.g., for a misconception that appeared as a distractor in 3 different items we divided by 3).
This misconception appeared as a distractor in three different items (one newly written item, one item revised from the study 1 instrument, and one item identical to the study 1 instrument; see Additional file 1: Table S11).
Gould, following Wimsatt, even goes so far as to argue that the causal agents in selection are the interactors, and that genes and other replicators are "important in evolution, but in a different role as items for bookkeeping.
Rasch analysis can assist in identifying differential item functioning (DIF), which occurs when different groups of people within the sample responded in a different way to an item despite equal levels of the construct that was measured.
In contrast, incongruent trials included displays in which a given participant's anchor points appeared in different items (e.g., incongruent trials for a participant biased toward tall-dark items included trials with [dark-short light-tall] and [light-tall dark-short] configurations).
"Firefly recognizes a hundred million different items in real-world situations," Bezos said.
