Blocking

Blocking - Blocking neutralizes background variables that can not be eliminated by randomizing. It does so by spreading them across the experiment.

You can think of a block as an kind of uncontrolable factor that is added to the experiment. A block is ususally used when this uncontrolable factor cannot be avoided during the experiment, so it is incorporated into the experiment in a controlled way. The idea is to pull the variation due to the blocks out of the expermental error in order to reduce the experimental error and give the test more power.

Common examples of when blocking factors are used:

When you don't have enough units from one lot and are forced to use another lot, AND you suspect (maybe know) that there are important differences between lots. You then use (in a controlled manner) half of the units from one lot and half of the units from the other lot.

When you don't have enough test chambers for all the parts, AND you suspect (maybe know) that there are important differences in the effects between test chambers. You then assign (in a controlled manner) half of your units to one chamber and half to the other chamber.

The original use of blocking involved agricultural experiments. Researchers needed to use multiple fields or fields that has important intra-field variation. They would the potential fertility of a field as a block factor. Similar blocking might have been needed due to differences between edge-effects and center effects on crops grown.

[Category=Data Quality ]

Source: iSixSigma, 02 January 2011 09:56:44, https:web.archive.org/web/20111109014246/http:www.isixsigma.com/index.php?option=com_glossary

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Blocking - a technique used in classical DOE to remove the effects of unwanted noise or variability from the experimental response so that only the effects from the control factors are present in the response data.

[Category=Quality ]

Source: The Quality Portal, 02 April 2011 07:37:30, http://thequalityportal.com/glossary/b.htm

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Blocking  - Blocking means the freezing of data by the controller in a given moment for a specific period of time. Access to the data blocked is limited only to the competent people.

As provided by Article 15 of Regulation (EC) No 45/2001, the data subject shall have the right to obtain from the controller the blocking of data where:

* their accuracy is contested by the data subject, enabling though the controller to verify the accuracy, including the completeness of the data; or
* the controller no longer needs them for the accomplishment of its tasks but they have to be maintained for purposes of proof; or
* the processing is unlawful and the data subject opposes their erasure and demands their blocking instead.

Personal data blocked can only be processed for purposes of proof, or with the data subject's consent, or for the protection of the rights of a third party.

[Category=Data Security ]

Source: European Data Protection Supervisor, 25 July 2011 09:22:13, http://www.edps.europa.eu/EDPSWEB/edps/cache/off/EDPS/Dataprotection/Glossary