For example, one may be able to study seven factors using just eight experimental trials. Randomize the experimental run, if possible For industrial experiments, randomization is a process of performing experimental trials in a random order in which they are logically listed. It is generally recommended because an experimenter cannot always be certain that all important process variables affecting a response has been included and considered in the experiment. The purpose of randomization is to safeguard the experiment from the influence of lurking variables or noise, such as change of relative humidity, change of ambient temperature and so on. These changes, which often are time-related, can significantly influence the response.
Replication is a process of running the experimental trials in a random manner.
In contrast, repetition is a process of running the experimental trials under the same set up of machine parameters. In other words, the variation due to machine set up cannot be captured using repetition. Replication requires resetting of each trial condition and therefore the cost of the experiment and also the time taken to complete the experiment may be increased to some extent. The blocks can be batches of different shifts, different machines, raw materials and so on. More information on the blocking strategy can be obtained from Box, et al.