If one assumes (i) that individual economic units predict the values of random variables within a model by use of adaptive expectations functions of the type due to Koyck, (ii) that the parameters of these functions differ among individual economic units, and (iii) that "market expectations" are a weighted combination of individual expectations, then the function representing aggregate behavior is not a Koyck function, but rather some other function belonging to the general class of Pascal distributed lag functions.