Generating characteristics of users of an online system presented with content in a context relative to other content

A computer program product comprising a non-transitory computer-readable storage medium having instructions encoded thereon that, when executed by a processor, cause the processor to:

• maintain a plurality of content items at an online system for presentation to users of the online system;
• maintain information at the online system describing contexts in which the content items are presented to users of the online system identified by the online system relative to other content presented to the users of the online system;
• select a context in which one or more content items are presented relative to other content;
• identify users of the online system to whom one or more content items were presented in the selected context relative to other content from the information maintained at the online system;
• obtain characteristics of each of the identified users based information associated with the identified users by the online system;
• generate characteristics of users presented with one or more content items in the selected context from the obtained characteristics;
• store the generated characteristics in association with the selected context;
• receive a request to provide content to a client device for presentation, the request identifying the selected context;
• responsive to the online system being unable to identify a user associated with the client device associated with the request, retrieve the generated characteristics associated with the selected context;
• and
• include content items having at least a threshold number of targeting criteria satisfied by the generated characteristics associated with the selected contexts in one or more selection processes that select the content to provide to the client device.