In my opinion you can not. It should be two separate groups

Thanks! That is, what I assumed first. But then I found german articels, that recommend asking the same group of people and they call ist "Zero-Round" of the delphi...

If you have a sufficient number of participants to create a separate set of people for the second round I would do that, because otherwise you may get a criticism that the participants from the first round were simply repeating what they already told you.

I would also recommend going into the second round with different set of people to generate more ideas before reaching a conclusion.

Thanks to all of you for sharing your optinions with me! I decided to build two seperate groups of participants.

Best regards!