How important is the interview?

Along with the resume the interview is the tool of choice in selecting the person for the job.  However if not done correctly it is a very poor indicator of proper selection.
Studies have shown that interviews have no correlation or a very weak bias to successful selection in most cases.   

The reasons are all related to human behaviour.  There is a range of effects that occur during the interview process and some of these include:

• Likeability Effect
  The person appears to be just like me.  Same social economic group, same school, culture, religion, same friends etc so we like them more.  All these things are unrelated to performance but it distorts our judgement.  We are more likely to make a bad decision.
• The Halo and Horns Effect
  This is where we attribute skills and abilities to people when we like them even though they have not demonstrated these skills and abilities – Halo Effect.  The opposite is true for the Horns Effect.  
• The Expectancy Effect
  This is where too much weight is given to the information in the resume and creates a bias in asking questions and perceiving the responses.
• Negative Information Bias
  Too much weight is given to negative information that may not be all that important or relevant.
• The Self-fulfilling Prophecy Effect
  This where all the questioning is around what has been stated in the resume.  It is the same as the effect of leading questioning where the answers are embedded in the question.
• The Information Overload Effect
  When people are overloaded with information they make judgement based on little information that leads to error.

There are many more effects than those described above but these are the more common.

The interview process is important but if not applied well a very blunt tool.

The best approach is to have a very structured interview process that suspends emotion and focuses on facts.  It should be objective and focused only on the criteria that must be observed and can be demonstrated.  

Once this has been done and the candidate has qualified then, and only then, can one bring into play factors around suitability for the team and the culture of the group.