Workers who boast that they can multitask are actually the worst at doing several things at once and at focusing on single jobs, according to a new study.

Serial multitaskers end juggling two activities at once not because they are good at it but because they are easily distracted and cannot concentrate on the job at hand, researchers said.

Conversely, the people who are the most adept at multitasking are the least likely to do so because they are better at focusing on doing one thing at a time.

The study also found that 70 per cent of people believe they are better than average at multitasking, which is statistically impossible.

Prof David Strayer, senior author of the study, said: “The people who are most likely to multitask harbour the illusion they are better than average at it, when in fact they are no better than average and often worse.”

The researchers, from the University of Utah, subjected 310 volunteers to tests and questionnaires designed to measure their actual multitasking ability against their imagined multitasking ability.

They also recorded how likely the participants were to use their mobile phone while driving or use a wide array of electronic media, and personality traits like impulsivity.

People who scored highly on the multitasking test tended not to multitask as much as others because they were better at focusing on completing one job at a time, results showed.

In contrast those who scored poorly at multitasking were more likely to end up doing so because they were more impulsive and easily distracted, and had an inflated sense of their ability to carry out two jobs at once.

“If you have people multitasking a lot, you might come to the conclusion that they are good at multitasking. In fat, the more likely they are to do it, the more likely they are to be bad at it,” Prof Strayer said.

“The people who multitask the most tend to be impulsive, sensation-seeking, overconfident of their multitasking abilities, and they tend to be less capable of multitasking.”

Overestimating one’s own capacity to perform multiple jobs at once could lead to dangerous consequences, the researchers warned.

Prof David Sanbonmatsu, who co-wrote the paper published in thePublic Library of Science Journal,