You can’t very well treat core instability if you can’t diagnose it as a problem in the first place. This test of the reliability of core strength testing was a clear failure: “6 clinical core stability tests are not reliable when a 4-point visual scoring assessment is used.” Even if core strength is important (a separate question), this evidence clearly shows that no one should be claiming to be able to detect a problem with core weakness in the first place. A bit problematic for core dogma.
Just added this citation to my article about reliability studies—it's a really good example of poor reliability. Later I will add it to a half dozen more articles.