The selection is not exhaustive.
    Below is an explanation of practical terms and expressions.

Methodology
[ How?  ]

     The Internet presents a problem to compare.
    Since there is no registry of all Internet banner exchanges, completing a chart, is very time consuming. This survey attempt to answer questions about all North America banner exchanges by selecting a set of features common to participants in that group.
     This process will determinate a set of points that we use to compare different services.
      Each feature will give a banner company one points for a total of seven.
     The exchange ratio as such does not gives any more or less points to the company and is only for information purpose

Sampling
[ one kind   ]

     Given that the sample was selected by hand , and each exchange had an equal chance of being selected for the sampling, results obtained from comparing the features be can generalized to the all companies.
    After all, the whole purpose of a comparison is to collect data on a group and choose THE banner exchange.