"creationists presuppose creation"

And that's just the problem. Creationists (think they) know the answer already (so why bother with data?) and then they manipulate the data to give them the answer they (think they) know already! Manipulating the data to give you the answer you want is called 'fiddling' or 'fudging' or 'cheating' or 'downright dishonest' or however you want to phrase it. If a real scientist tried that he/she wouldn't get past the peer review process ... but then a real scientist doesn't (almost by definition) know the answer already ... which is why she/he does science!