To study this issue, participants
are typically asked to choose the larger out of two fractions.
As any fraction is represented by two natural numbers,
relying solely on the values of these two natural numbers rather
than on the values of the whole fractions can lead to correct answers
in some cases (such as 4/5 > 3/5 because 4 > 3) but to
incorrect answers in others (such as 1/4 < 1/3 even though 4 > 3).
Thus, fraction comparison problems can be congruent (in the first
cases) or incongruent (in the second cases) with the way natural
numbers are processed. Assuming that individuals are biased by
natural numbers, they should perform better on congruent than on
incongruent fraction comparison problems. This has been found in
students of different grade levels of primary and secondary schools