To return to the question posed by the OP, "Evaluating a scientific claim," Karl Popper made some reached some conclusions about how to do that way back in 1920 He said the following:
- It is easy to obtain confirmations, or verifications, for nearly every theory--if we look for confirmations.
- Confirmations should count only if they are the result of risky predictions; that is to say, if, unenlightened by the theory in question, we should have expected an event which was incompatible with the theory--an event which would have refuted the theory.
- Every 'good' scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is.
- A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice.
- Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks.
- Confirming evidence should not count except when it is the result of a genuine test of the theory; and this means that it can be presented as a serious but unsuccessful attempt to falsify the theory.
- Some genuinely testable theories, when found to be false, are still upheld by their admirers--for example by introducing ad hoc some auxiliary assumption, or by re-interpreting the theory ad hoc in such a way that it escapes refutation. Such a procedure is always possible, but it rescues the theory from refutation only at the price of destroying, or at least lowering, its scientific status.
Popper summarizes by saying that "
...the criterion of the scientific status of a theory is its falsifiability, or
refutability, or
testability.
Other philosophers of science (Thomas Kuhn, Imre Lakatos, and Paul Thagard for example) have disagreed with Popper's requirement of falsifiability as a criterion of science. But I find it interesting that, even though each of these offer a different set of necessary conditions for genuine science, all reject 'creation science' as science.