Six million "lost" days cost small businesses an estimated €757 million last year, with stress the main reason listed on medical certificates for workers taking the day off, according to the Small Firms Association (SFA).

But the business lobby group's survey of small firms found that workers in small companies are less likely to miss work through illness than their counterparts in larger businesses.

Workers in small firms missed an average of seven days last year, compared to a national average of nine days, the SFA said.

The estimated €757 million per annum cost of absenteeism is based on the amount paid out by firms with sick pay schemes based on average earnings of €120 per day or €30,800 a year.

SFA assistant director Avine McNally said the figure didn't take into account the costs small businesses incurred when hiring replacement workers, making overtime payments and seeking medical referrals, as well as indirect costs such as the effect on productivity and the administration time spent on managing a worker's absence. "The overall cost in reality could be in excess of €1 billion," Ms McNally said.

Stress has replaced back pain as the most commonly cited problem on medical certificates, which the SFA described as "particularly concerning".

Ms McNally said employers should ensure that they were fulfilling their duty of care to their employees by assessing their stress risks as part of their review of health and safety procedures.

"They should also ensure that their employers' liability insurance will protect them against any compensation awards that may arise from this area," she said.

The SFA survey showed that absenteeism was most frequent in the electronics industry, where workers missed an average of 16 days a year.

This was followed by the engineering sector, where the average number of sick days was 11 days.

The SFA said the higher absence rates in those industries could be explained by the repetitive nature of the work involved.

Over half of the companies surveyed by the SFA said they recorded the causes of short-term absence.

Minor illnesses are the most common cause for short-term uncertified absences, while secondary causes include home responsibilities and personal problems.