As everyone knows, 'filtering' is a system used by most employers in order to get the best person for the job. Interviews, assessment centres, CVs, and, increasingly, psychometric tests are all included in the selection process

Employers like the tests as they help make the process easier. But what are they exactly?

Psychometric literally means 'to measure the brain' - but don't let that intimidate you! The tests are formed of aptitude tests and personality questionnaires and are used to determine a person's competence, skill, sensitivity, memory, intelligence and personality. There are no specific rules. For example, tests for management consultancy roles will be different to those for a sales manager.

Personality questionnaires, usually un-timed, help to work out how people are likely to behave in different situations, their social skills and work style. They are also used for self-assessment purposes to help people understand their strengths and weaknesses.

While it's easy to give what you think is the right answer, it's better to be yourself as the employer may be looking for a range of personalities rather than the one you think they want. Also, sophisticated testing methods mean it's easier to spot any inconsistent answers while not answering honestly means you may get a job that might make you miserable.

Unlike personality tests, which have no right or wrong answers, aptitude tests, which look at verbal, numerical and abstract reasoning, definitely do. They don't test general knowledge or intelligence but rather your potential, logic and thinking performance.

For example, the numerical test won't ask about algebra or trigonometry but will test your mental agility to determine how quickly you understand numbers. It may be worth freshening up on your times tables, percentages, fractions and long multiplication. You may be asked to complete a sequence of numbers, state the largest fraction or interpret date tables.

By the same token, verbal tests do not question your spelling skills but rather how you respond to written text. For example, you may be presented with a paragraph of text and asked to interpret the information. Logical reasoning usually involves spotting patterns in diagrams.

The tests are timed with multiple choice answers so working quickly and precisely is key. Like personality tests, they are also used for self-assessment as an aid to career development. The way the tests are conducted varies from employer to employer. You may be invited to do it online or at their offices and typically, there may be 30 questions to answer in about 30 minutes. Scores are generally compared to those of other candidates for employers to compare potential.

Dr Mark Parkinson, business psychologist and author of the bestselling How to Master Psychometric Tests, explains: 'Tests are measuring 'maximum' performance (how good you are at something); whereas questionnaires are measuring 'typical' performance (what you're usually like). Of course, questionnaires do not have right or wrong answers, but they tell us something about how you might behave or act, or what your values, attitudes or interests might be.'

Some employers use the tests before interviews as a way of screening the best applicants while others employ them at the final stages when only a handful of candidates remain.

As Mark Parkinson says: 'Tests represent an impartial way of finding out about somebody. But, like exams, some people dislike doing them and interestingly, if an employer announces that tests are to be used as part of a selection process, up to 40 per cent of applicants will not turn up - a startling figure which shows just how many people fear formal assessments.

'Employers should bear exam nerves in mind when viewing results and because the tests are timed, any condition that slows a person down (dyslexia, poor shoulder/hand movement and eyesight problems) is likely to lead to lower scores.'

Of course, tests are only part of the process. 'Tests are applicable in most situations, but they are just tools,' emphasises Mark Parkinson. 'Employers shouldn't slavishly adhere to test results as sometimes the more creative individual, or indeed, some high-flyers, do not necessary get good results. Tests should be used as part of a more rounded selection process. The most common mistake is to select tests/questionnaires that don't assess the right things. Naturally, this isn't fair and could even lead to recruiting the wrong person.'

If you're about to go for a psychometric test, you can certainly prepare for aptitude questions. See if your local careers centre offers practice sessions or on the daily commute, try maths teasers, crosswords, word games and puzzles to give your brain cells a workout.

Speed and accuracy are both of the essence so bear that in mind too. If you Google 'psychometric tests', you will find numerous free tests which provide great practice material.

Lisa McGann, who recently sat psychometric tests for her current job, says: 'While it's not something you can revise, you can prepare yourself on what to expect and get a feeling of how the questions are structured and phrased.

'Also, you may find you're better at some things than you imagined. For example, you may not think you can do logical thinking but I could. And, because it's timed, just trust your intuition when the answer is not obvious!'