Popper argued that observation is selective and theory-laden and that there can be no pure or theory-free observations. He further argued that it is possible to select amongst observable data in such a way as to support personally favoured yet invalid theories.
(So-called creation 'science' and intelligent [sick] design theory are not science, and provide clear examples of the misinterpretation and misrepresentation of facts to fit a prior insistence on the existence of a creator. Here, I use prior to indicate that belief in a creator comes prior to the manipulation of the data to support the belief. Creation myths are the invention of humans in almost every culture and are initially invented because of a psychological need for an a posteriori explanation of the natural world. Continuation of such creation mythologies are ensured by post-invention indoctrination.)
Regarding Karl Popper on the topic of the demarcation of science from non-science:
"Formally, then, Popper's theory of demarcation may be articulated as follows: where a ‘basic statement’ is to be understood as a particular observation-report, then we may say that a theory is scientific if and only if it divides the class of basic statements into the following two non-empty sub-classes: (a) the class of all those basic statements with which it is inconsistent, or which it prohibits — this is the class of its potential falsifiers (i.e., those statements which, if true, falsify the whole theory), and (b) the class of those basic statements with which it is consistent, or which it permits (i.e., those statements which, if true, corroborate it, or bear it out)."
Thornton, Stephen, "Karl Popper", The Stanford Encyclopedia of Philosophy (Winter 2006 Edition), Edward N. Zalta (ed.), URL