Philosophy as literature is not measurable.

Philosophy as logic doesn't need to be measured because you can prove things--that's even more reliable than gathering evidence.

Any other philosophy is measurable in the same way as you measure anything else: you make predictions about what should be the case and go measure things that, depending on how they come out, may illuminate flaws in your model.

Psychology is almost completely measurable.

It can be difficult to make measurements with enough precision and with enough control to be able to discern patterns of causality, so it's certainly challenging work. That doesn't mean it's impossible; you either accept the challenge and do tough experiments, making slow but real progress; or you decide that it's too tough and veer into non-science.