It's a representative study, done by a major institute for opinion research[1][2], comissioned by a major newspaper[3][4].

[1]: https://en.wikipedia.org/wiki/Allensbach_Institute

[2]: https://www.ifd-allensbach.de/fileadmin/user_upload/FAZ_Mai2...

[3]: https://en.wikipedia.org/wiki/Frankfurter_Allgemeine_Zeitung

[4]: https://www.faz.net/aktuell/politik/inland/allensbach-umfrag...