# Design of Experiments

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• #23923

klaus
Participant

what is the difference between repetition and replication – with respect to setting up a DOE ?

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#57269

Participant

A replication is a repeated run of the experiment at the same experimental conditions. It is used to provide an estimate of the pure trial to trial “experimental error” or “noise” in a process and allows for more precise estimates of the treatment effects.
Repetition could mean anything. If repetition were performed under the same experimental conditions,then repetition = replication.

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#57271

Stefan Szemkus
Participant

Klaus,
to replicate means to repeat the entire design. A 2**3 full factorial DOE contains 8 cornerpoints (=combinations). If you do 2 replicates you have to do 16 runs, so you repeat every treatment combination once. This allows, like mentioned in an earlier answer, the estimation of your experimental error.
Repeat is the repetiton of a single treatment combination. If your process does not allow fast changes (continues process like tube mill) replicates are very difficult so its adequate to take multiple sample at the same teatment combination.

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#57274

K.M.Date
Participant

Repetition: Repeated measurements/observations on the same item/unit produced/made/processed under a given set of conditions.Replication: Measurements/observations on different items/units produced/made/processed under the same set of conditions, but at different times.

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#57278

Tommy VanHorne
Member

The importance in knowing the difference between replication and repitition lies in the degrees of freedom allowed into the experiment for determination of significant effects.  In DOE, if you design an eight treatment combinations in your experiment and run a repeat of each treatment back to back, you have 8 degrees o freedom in the experiment.  If you randomize the 16 runs (8 treatment combinations repliacted somewhere in the experiment) and few if any are run consecutively, you have 16 degrees of freedom.  Subtle, but important.

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#57553

wilma
Member

which is better? repitition or replication

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#57585

Monica Suede
Participant

About the differences between REPLICATION and REPETITION, the answers that have been showed in this discussion still not enough. So, I would like know if replication is better than repetition, because this design technique can bring us aditional information, such as the effects of the some condition or machine or operator or raw material.

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#57743

HY
Participant

Replication is to repeat the whole set of combinations after all runs are done. Repetition is to repeat one experiment before doing another combination, which means doing the same combinations together before changing conditions. Replication is statistically better since it avoids systematic errors but more expensive.

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