The survey was carried out by the GFS Bern research institute on behalf of SRG SSR between 23 and 31 May 2023. Overall, the answers of 12,655 voters were taken into account for the evaluation.
1,204 eligible voters residing in Switzerland were surveyed by telephone. The interviews were conducted via landline and mobile phones.
This sample is weighted according to language region and is representative of Swiss voters. The statistical error is ± 2.8 percentage points. With 1204 respondents and a result of 50 percent, the effective value is between 47.2 and 52.8 percent with a 95 percent probability. Smaller deviations are more likely, larger ones less likely.
online survey
In addition, several thousand people were surveyed online. After cleaning and checking the data, the information from 11,451 voters could be used for the evaluation. The online survey was implemented via the web portals of the SRG media as a so-called opt-in (participatory survey).
This online sampling was not random and the resulting sample is not representative. For example, fewer older people than younger people took part in the online survey and more men than women.
For this reason, the Institute GFS Bern weighted the answers: The distortions in the sample were counteracted using statistical weighting methods, thus optimizing the representativeness.
The breakdown of the respondents by language region is as follows: 10,334 in German-speaking Switzerland, 2,011 in French-speaking Switzerland and 310 in Italian-speaking Switzerland.
How is the question asked?
The voters surveyed each had five possible answers: “definitely in favor”, “rather for”, “don’t know/no answer”, “definitely against” and “rather against”.
For a simplified presentation in the article, the answers “definitely for” and “rather for” were added together in most cases – the answers “definitely against” and “rather against” were dealt with in the same way.
Specifically, the question was asked: “Regardless of how certain you are that you will take part in this referendum: If the bill were voted on tomorrow, would you be in favor, more in favor, more against or definitely against?”
Polls are snapshots
The research institute JRC Bern conducted two surveys on the vote of June 18, 2023. The authors of the study emphasize that the results are not an anticipated result of the vote, but a snapshot at the time of the survey. However, statements about trends are possible in two surveys.
Detailed information on the type of survey and the interpretation of the results can be found on the institute’s website JRC Bern.