Replication is performing the same treatment combination more than once to increase confidence in those findings; repetition of the same research procedures (usually by a second researcher) for the purpose of determining if earlier results can be duplicated; the collection of two or more observations under a set of identical experimental conditions. Repeating the creation of a phenomenon, so that the variability associated with the phenomenon can be estimated. If affordable, replication should be part of every design. Replication allows us to compute a model-independent estimate of the process standard deviation. Such an estimate may then be used as a criterion in an objective goodness of fit test to assess whether a given model is adequate. Such an objective test can be employed only if the design has built-in replication. Some replication is essential; replication at every point is ideal.