A lot of research on interviews has shown they basically don't work. You just can't grill someone for a few hours and know how they're going to do on the job.
For unemployed candidates, we should do away with interviews altogether and do paid 2-week trials instead. After the first 2-3 PRs it's pretty clear if someone has the skills you need and to what degree. It would also help the candidate decide if they like the company.
Employed candidates are harder to evaluate and I don't think there's a single formula that will work for every company.