The present study was conducted to examine if the cognitive representation
of subjective probability could be better objectified. Subjects were requir
ed to play a commercial slot machine and afterwards make an estimation as t
o the machine's percentage of payback. A linear regression analysis indicat
ed that such a subjective probability estimation is developed by a combinat
ion of the number of coins played, the number of coins won, and the number
of winning games. These findings suggest that examining such environmental
variables may provide an explanation for the development of subjective prob
abilities.