A pattern probability (302) is determined for each of a number of target
patterns (301) achievable in a bingo-type game. Each pattern probability
(302) comprises a probability of achieving the respective target pattern
(301) in the bingo-type game. Different pattern sets are then associated
with each different prize level in a desired prize distribution. The
target patterns (301) and their respective pattern probabilities (302)
are assigned or mapped to the different pattern sets so that the
probability of achieving any target pattern included in a pattern set
comprises a value approximating the desired probability of the prize
level with which the pattern set is associated.