Although reasons are critical to supporting a claim, without evidence they carry little weight. An audience is unlikely to be persuaded to accept a claim on the basis of reasons alone, particularly if that audience holds a drastically different position than you/the author(s). Evidence can be defined as information that supports the reasons, demonstrating why they are sound ideas (that support the claim).
We tend to think of evidence in terms of statistics (or quantitative data) since people find truth in numbers. Be aware, though, that evidence does not have to be numerical; instead, evidence can take the form of an anecdote (a brief account or story), excerpts from a conversation or an interview, a quotation from a published source, an image or graphic, etc. Also keep in mind that a statistic is not necessarily accurate; just as a quotation can be taken out of context, numbers can also be manipulated. As an audience member, you must be skeptical of the evidence someone presents to you, but, likewise as a writer, you must be diligent in evaluating the credibility and applicability of any information you come across that you intend to present in support of your argument.