The concept of aptitude testing can be dated back to before 2000 BC, with the ancient Chinese using a rudimentary ability test to assess the abilities of prospective civil service workers. When western diplomats learned of this Chinese selection procedure, the British East India Company emulated this system in 1832, and thus, aptitude testing was introduced to the western world.

However, it wasn’t until the work of the Victorian polymath, Sir Francis Galton, did the first scientific ventures into psychometrics begin. Inventing and subsequently applying concepts such as correlation, normal distribution and regression allowed Galton to measure and correlate intelligence with other variables. Following the work of Francis Galton, other psychometricians have since made huge advances in the field of psychometrics, intelligence and personality testing, including Karl Pearson, L.L Thurstone, Raymond Cattell and Hans Eysenck.

Psychometrics for selection and assessment didn’t become big business, however, until the formation of the psychometric test publisher SHL, by eminent occupational psychologists Peter Saville and Roger Holdsworth. SHL quickly become the largest publisher of psychometric tests worldwide, spearheading the movement for the use of ability and personality testing in the workplace. Today, virtually all large UK organisations throughout the public, private and third sector use psychometric testing at some stage of their recruitment, selection and development programs.

How they work

Psychologists have correlated the results of psychometric tests with job performance, and found a moderate-strong correlation between high performance on these tests, and high performance at work. Academics, occupational psychology consultancies and psychometric test publishers have spent decades and millions of pounds on research and development in order to ensure the reliability and validity of these tests. It is worth noting however, that high performance on these tests does not correlate perfectly, and some individuals may score highly, but perform poorly at work, or vice versa.

Psychometricians and psychologists have to conduct research into the reliability and validity of psychometric tests before they can be used for selection procedures. Reliability is the consistency of a test's scores under consistent conditions. For example this may be tested by getting candidates to retake tests, comparing the scores against two groups of people and by assessing the consistency of the scores within the test itself. In order to be valid, it is necessary for a test to be reliable. Validity is the degree in which a measure is supported by the relevant theory and evidence. For example, a test which scores strongly correlate with job performance would be considered a valid test.

Once the candidate has completed the test, their results are compared against a norm group, a collection of hundreds, even thousands of previous results, in order to compare against the average score. These norm groups will be candidate specific, for example if the test candidate is a graduate, a norm group of graduates will be utilised etc. The scores are then expressed as a percentile rank, i.e. a score within the 50th percentile means the candidate scored better than 50% of the individuals within the norm group. The higher the percentile rank, the higher the candidate has scored compared to the norm group. Generally speaking, if psychometric testing is being used as a screening process, organisations will set a cut off rate at the 40th percentile, screening out candidates that achieve scores below that point.

Why they are used?

Well researched, highly reliable and valid psychometric ability tests have been found to be the single most effective predictor of job performance available. Psychometric tests have outperformed interviews, references, bio-data and every other commonly used assessment procedure in an occupational setting. Therefore, it is no surprise that organisations are increasingly turning to psychometric testing to assess prospective candidates, and to assess the abilities of their workforces. Similarly, the predictive power of psychometric testing, combined with other selection/assessment procedures such as competency based interviews, assessment centre exercises and other valid selection methods, is significantly higher than either measure on their own.

Research has also shown that other selection methods, such as interviews, are susceptible to subjective influences. Interviewers may be swayed to make selection decisions based on irrelevant factors, such as physical appearance. Psychometric testing is a fair and objective method of selection, which is free from subjective influences or bias. Psychometric ability testing is seen as a meritocratic method of selection, helping ensure that selection decisions are made based due to a candidate’s ability, using evidence based practices.

Psychometric testing provides an objective, scientific and highly accurate method of selection to employers around the world. Increasingly, employing organisations are turning to psychometric testing to meet their recruitment, selection and development needs. The more you understand about how psychometrics work and why they are used, the better prepared you will be to undertake one, helping ready you for any future psychometric test which an employer would ask you to take.