10. A method comprising: receiving a plurality of posts of content from users of an online system; receiving a request from a viewing user of the online system for posts associated with a plurality of other users of the online system; selecting at least two candidate posts for the viewing user, the at least two candidate posts associated with one or more other users of the online system; receiving, for each of a plurality of types of interaction that the viewing user may have with each candidate story, a value to the social networking system of the viewing user performing the type of interaction on a candidate story; for each of the plurality of types of interaction, determining a probability of the viewing user performing the type of interaction on a candidate story; computing an expected value score for each of the selected at least two candidate stories, the expected value score based on: for each of the plurality of types of interaction, (1) the probability of the viewing user performing the type of interaction on a candidate story, and (2) the value to the social networking system of the viewing user performing the type of interaction on a candidate story; ranking the selected at least two candidate posts based at least in part on the expected value scores; selecting a set of the candidate posts based at least in part on the ranking; and sending the selected candidate posts for display to the viewing user.
10. A method comprising: receiving a plurality of posts of content from users of an online system; receiving a request from a viewing user of the online system for posts associated with a plurality of other users of the online system; selecting at least two candidate posts for the viewing user, the at least two candidate posts associated with one or more other users of the online system; receiving, for each of a plurality of types of interaction that the viewing user may have with each candidate story, a value to the social networking system of the viewing user performing the type of interaction on a candidate story; for each of the plurality of types of interaction, determining a probability of the viewing user performing the type of interaction on a candidate story; computing an expected value score for each of the selected at least two candidate stories, the expected value score based on: for each of the plurality of types of interaction, (1) the probability of the viewing user performing the type of interaction on a candidate story, and (2) the value to the social networking system of the viewing user performing the type of interaction on a candidate story; ranking the selected at least two candidate posts based at least in part on the expected value scores; selecting a set of the candidate posts based at least in part on the ranking; and sending the selected candidate posts for display to the viewing user. 14. The method of claim 10 , wherein computing the expected value score for each of the selected at least two candidate posts comprises: for each of the plurality of types of interaction, calculating a product of a value for a type of interaction and a probability that the viewing user will perform the type of interaction on the candidate post; and calculating a sum of the products.