Methods and systems for determining the effect of a host on network latency while delivering online ads are disclosed. Observational test data relating to one or more network latency tests conducted on a plurality of hosts may be obtained. A first group and a second group of hosts may be created, wherein the first group includes the host and the second group doesn't include the host. At least one predetermined metric for each of the first group and the second group is computed based on the test data. A ratio of the at least one predetermined metric for the first group to the at least one predetermined metric for the second group is computed. The host may then be ranked based at least in part on the ratio.