I don't think interviews, even with technical components, can tell you even with 75% certainty how a candidate is going to perform at the actual job. There are considerations like work ethic and how well someone can grok the actual issues the company faces (as opposed to a toy problem) that you just can't really know until they're actually doing the work (or not). Some people are really smart but turn out to be lazy. How do you weed them out in an interview?