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Random Selection for Questionnaires

Multiple questionnaires can be created in one survey project (Compose QuestionnaireFurther questionnaires tab). If the participant calls up the URL to the Questionnaire, it can be randomly assigned to one of the questionnaires. There are options explained at the bottom in Compose QuestionnaireFurther questionnaires tab → Random Selection for Questionnaires which can be selected in order to achieve this.

Note: Random selection of questionnaires has some restrictions (see notes below) and this option is only sensible in a few exceptional cases. As a rule, it makes much more sense to use normal randomization.


Selection or random selection takes place every time the project folder is selected without a specific questionnaire being specified (URL to the questionnaire). This address (URL) is found under Survey ProjectProject SettingsProject folder.

In an unrestricted random selection, the different conditions will usually usually drawn an unequal (!) number of times. If 100 people are spread across 5 groups, the groups could be distributed as follows: 32, 7, 13, 28, 20. The larger the subgroups, the more unlikely (not impossible!) there will be disproportional variations. If groups of the same size are required, a randomization with urns within a questionnaire is the method of choice.

The same goes for a weighted random selection: as a rule, approximation to the desired distribution only occurs in the region of larger numbers (n > 1000). Statistical outliers are therefore not possible either.

The questionnaire a participant fills in is always noted in the variable QUESTNNR (Additional Variables in the Data Set) in the data record. This applies to the explicit selection of the questionnaire in the link, just like the random selection of a questionnaire.

Set Questionnaire as Default

One of the questionnaires will be used as default if this option is chosen. The link to the survey project will then always lead to the same questionnaire - except when another questionnaire is explicitly specified in the link.

If only one questionnaires exists in the survey project then this questionnaire will always be used as default.

Random Selection from Selected Questionnaires

One or more questionnaires can be selected with this option. If the URL is called up without a questionnaire being specified (see above), this means one of the selected questionnaires will be chosen at random.

Note: As a rule, an unrestricted random selection results in questionnaires being called up different numbers of times. Therefore, please take the information above into consideration.

Weighted Random Selection

Weighted random selection represents an extension of a random selection. The principle is the same as a random selection: one of the questionnaires from those with specified weighting (i.e. not 0) will be selected at random.

Questionnaires with a higher weighting are therefore chosen with a correspondingly higher probability. The specific numbers that are input is not important, what matters is the relation: a questionnaire with a weighting of 2 will be (for example) selected twice as often as one with a weighting of 1. A questionnaire with a weighting off 66 will be selected twice as often as a questionnaire with a weighting of 33.

en/create/random_questionnaire.txt · Last modified: 05.02.2015 11:23 by alexander.ritter
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