One way in which you can identify an author's claim is by identifying the author's purpose. An author writes an essay or some other type of text because he wants to communicate something specific. The idea he wants to communicate is his claim. The rest of the text, therefore, will be designed to persuade the readers to support his point of view.
I don't know this for sure but if an author has something to declare and they can't back it up it's just an idea. So if you want to identify the claim you have to have statistics and facts to prove what you're saying. But remember I am not am expert so whatever you think the answer is go with it. Hope this helps ;)
