Randomization

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There are different types of randomization, the technical implementation of which differs in some cases considerably:

1. Randomization: Single-factorial design (Contains the introduction - please read first!)
   Participants are assigned to different experimental groups and are presented with a random stimulus (image, video, audio). Conceptually, it is a division into different groups.
2. Randomization with PHP-Code
   If the display options of the above solution are not sufficient or if questions or texts (also together) are to be randomized, the interaction of random generator and PHP code is explained here. However, this chapter is only about the integration of the stimulus into the questionnaire. Therefore, it is recommended to read the first chapter before.
3. Randomisation: Multi-factorial design
   Participants are divided into different experimental groups and are presented with several random stimuli (questions, pictures, videos, texts ect.).
4. Randomization within-subject (Measurement repetition)
   Participants are shown several stimuli, and these stimuli can be combined in different ways, always asking the same thing.

Tip: To understand the more complex code examples, read the chapters Introduction to PHP Code and Introduction to Arrays.

Tip: Also check out the https://cast.itunes.uni-muenchen.de/clips/H2qJPn0rX8/vod/online.html on randomization for a better understanding and using a concrete example.

Note: In distinction to randomization there is also Rotation. Here, the order in which the stimuli are presented is randomized.

• Block-Randomization
  Block randomization ensures equal distribution within (e.g. demographic) subgroups.
• Random Selection for Questionnaires
  In individual cases, it may be useful to work with separate questionnaires.