Doing what you're doing will probably work, in that you'll get decent candidates. But this approach only works for one kind of good developer -- the kind who can survive this kind of interview. Silicon Valley's diversity problem is made worse by interview styles that give false negatives for excellent candidates who lack confidence or just don't think the same way. My thesis is that this test, by giving frequent false negatives, is resulting in a worse pool of final hires than a broader process.