The letter arrives from the potential employer. Yes! You’ve been short-listed. But how do you respond to the rest of the letter? You’ve been invited to attend an assessment centre… Do you groan, or take it in your stride?

We’ve just had privileged access to the responses of over 200 senior people in the NHS who have been through one of our assessment centres. They were competing for jobs as chief executives in the new Primary Care Trusts (PCTs) and later (different cohorts) for jobs as directors of PCTs and Strategic Health Authorities.

Others have been competing for jobs as planning managers in workforce confederations. Interestingly, at the same time, we have been helping a media client, The Telegraph Group, appoint salespeople – an apparently very different field – through an assessment centre approach.

First, of course, there is apprehension, especially for people who have never been through an assessment centre before. "What I am going to be asked to do? How should I behave?". This figures largely in our candidates’ initial responses.

Some people believed that they were going to be asked to lie on the floor holding hands, or that they were going to be asked to do some kind of team-building activity. Building a raft seems to have been a popular fantasy here, though quite how we would have accomplished this within the somewhat limited environment and sober atmosphere of the Lloyds Building in the City of London, where we held the centres, is a bit of a conundrum.

Underlying this feeling was a common concern. Many of our candidates had sailed through their careers previously. The recent root and branch reform of the NHS has meant that for some, the smooth escalator of their careers has come to an abrupt halt. Now they are having to be judged, often for the first time, against objective criteria that were very tough indeed.

In subsequent coaching sessions, many of these clients have confessed to what we might call impostor syndrome – "Oh no, someone’s going to find me out!"

"I’m awful at tests", "I hate feeling judged", "I’m terrified it’s going to shatter my confidence". These feelings are admitted by senior, highly competent people.

If these seem like all-too-human fears about what the process might reveal, the majority of our client-candidates have reported strongly positive responses to the basic proposition of the assessment centre process.

A good assessment centre simulates a day in the life of a successful person doing the job for which you are competing. The appointing panel gets an objectively written report about how you have done against these criteria. By doing this, they can access more information about you than they could get in any other way.

Panel interviews are a notoriously unreliable way of predicting future success in the job. By adding an assessment centre, the panel’s decision will be based on real data rather than prejudice and assumption. Also, the perceived fairness of the process is greatly increased.

Similarly, from the candidate’s point of view, the assessment centre may help you see that this is not really the job for you – or, gloriously, that it is. As one such candidate said, "I was very twitchy about coming here, but actually, if this is what the job is – I want it!". We are glad to report that she got the job.

"It was very realistic ... In a weird way it was fun".

In doing this work, we have been interested to hear about our client’s wider experiences of assessment centres. How do you judge whether the one you have been through is any good? Here is a list of elements you should look for: