At my job we have fairly frequent meetings with either ill-defined agendas, or agendas that are a long list of subjects with no central theme - basically "the team should meet to talk about anything anyone feels should be brought up" meetings, with or without everyone emailing a list of what they want to talk about in advance. (I'm not in charge of organizing them, although I could suggest a different model if anyone has a good alternative.)
At some meetings, there turns out to be nothing that's relevant to my part of the job, or else we go over most of the points of the list quickly and then end up spending half an hour on something I can't contribute to. (Most of the team does hands-on science, I just do the data analysis). Is there any polite way for me to excuse myself from the meeting when it becomes clear there is no reason for me to be there? Or would it be a bad idea to try at all?