1. A computer-executed method comprising: detecting first activity, of a user associated with a particular entity, said first activity related to a first topic of a set of topics; in response to detecting the first activity, modifying a first subset of bits, of a first set of bits associated with the particular entity, to reflect the first activity related to the first topic; detecting second activity of the user, said second activity related to a second topic of the set of topics; in response to detecting the second activity, modifying a second subset of bits, of the first set of bits, to reflect the second activity related to the second topic; wherein the first subset of bits is distinct from the second subset of bits; wherein the position of each bit of the first subset of bits indicates which topic of the set of topics that the first subset of bits reflects; wherein the position of each bit of the second subset of bits indicates which topic of the set of topics that the second subset of bits reflects; wherein a quantity of the first subset of bits is different than a quantity of the second subset of bits; determining a value for the first topic based, at least in part, on the first subset of bits: dividing the value for the first topic by a range of values that can be represented by the first subset of bits, to produce a normalized value for the first topic; selecting a particular content item from a plurality of available content items based at least in part on the first set of bits; and wherein the step of selecting the particular content item from the plurality of available content items further comprises selecting the particular content item based, at least in part, on the normalized value for the first topic; displaying the particular content item; and wherein the method is performed by one or more computing devices.