A method and apparatus for determining what level of performance must be maintained by a second communication service (910) so as to be perceived as being of equal quality to a first communication service, especially where the second communication service (910) is subject to additional impairments (972) not experienced by the first communication service. In one example embodiment, the present invention is applied to determining what combinations of packet loss rate (968) and packet delay are tolerable where a packet switched telephony service is desired to be perceived to be substantially equivalent to a traditional toll-quality non-packet switched telephone service. Empirically derived models (940) are used to relate user perception to objectively measurable characteristics, such as packet loss rate (968).