One of the main reasons that a lot of golf players do not spend more time developing a better mental strategy in their game is probably because it is quite difficult to measure this progress. In fact, you would not touch or see a mental game, while you would quickly notice the difference when changing your equipment or adjusting a swing. So how can you know whether you are getting a positive result on your time devoted to improve your golf mental skills?
In general, you need to learn the definition of mental skills before you can measure it. Being a mental coach for many years, I would talk about this topic for hours, but to put it simply, it is how well you are able to access a best game when playing under the pressure. In other words, it is all about how well you could block the negative distraction out distractions and pay attention to the element that is going to offer you the best opportunity to be successful in a golf game. If you can play well in practice, but find it challenging in competition, this would mean that you need to improve your mental skills more.