Industry observers are questioning a recent National Institute of Occupational Safety and Health (NIOSH) study critical of back supports that appeared in the Journal of the American Medical Association.
Ergodyne, a Minnesota-based company that develops ergonomics products and programs is pointing to conclusions contradicted by the data, careless research methodology, and other deficiencies in the study.
The article, "A Prospective Study of Back Belts for Prevention of Back Pain and Injury," reported the findings of a two-year study by NIOSH of workers at selected Wal-Mart stores.
Some stores were designated for "mandatory" belt use while other stores were designated for "voluntary" belt use.
Ergodyne pointed out that 9,377 employees provided base interviews, but only 6,311 completed the follow-up interviews performed by phone approximately six months after the baseline.
"The validity of the research is less than exceptional and can only be described as ''quasi-experimental,''" said Howard Huber with Ergodyne. "NIOSH made significant mistakes in organizing their data and the combining of data sets, selection bias, recall bias and lack of any control group make the conclusions drawn by NIOSH faulty and far from conclusive."
In the stores requiring mandatory belt usage, only 58 percent of employees reported wearing the belt "usually every day."
Meanwhile, in the stores designated for voluntary belt usage, fully 33 percent of employees reported using the belts "usually every day."
Since belt usage was so similar across stores, it is virtually impossible to distinguish the difference statistically, said Huber.
Ergodyne said this distinction is compounded by the fact that confirmation of belt usage was performed by phone during the six month follow-up interview.
"The interviewer asked only about the previous month of belt use, not the previous six months of the study," said Huber. "NIOSH can only assume belt usage and therefore can only offer opinions rather than scientific conclusions."
Ergodyne also pointed out that the study includes some lost data.
Employees were assigned to one of four different categories of belt usage based on their phone interview: "usually every day", "once or twice a week," "once or twice a month" or "never."
"For some unexplained reason, NIOSH combined the ''once or twice a month'' with the ''never'' group," said Huber. "This can only distort the ultimate findings. There were also 3,155 employees of the baseline group that were not followed up with an interview. This raises multiple questions. Why? Who were these workers? What was their back belt wearing status? What was their lifting status? This represents lost data that NIOSH does not explain."
Ergodyne noted that selection bias is one of the most devastating problems in the back belt study.
"Employees who reported wearing a belt ''usually every day'' were more likely to be receivers/unloaders or stockers and also more likely to report lifting more than 20 pounds at work usually every day," said Huber.
"These job classifications were the ones most ''at risk'' for back pain and injury," continued Huber. "It would be similar to reporting that, of several hospitals, the only one in town that accepts seriously ill or critically injured people provides poor service because a greater proportion of patients die there. This is just not a fair comparison. If some correction for this bias is not introduced, and it was not, then the deck is stacked against finding that back belts are protective."
Ergodyne noted that "OSHA says evidence supporting back belts is ''voluminous.''"
OSHA recently reviewed all of the current research on this topic including more than 26 epidemiological and clinical studies supporting the effectiveness of back supports.
OSHA stated in its final version of the ergonomic standard that, "OSHA''s review of the voluminous record on the back belt issue shows that back belt may have protective effects in certain industrial settings, such as sudden unexpected loading of the spine. The Agency is persuaded that the evidence for the effectiveness of back belts, although limited, exceeds that available for other types of equipment workers wear that is classified as PPE (e.g., palms pads, kneepads). OSHA has therefore decided not to prohibit the classification of back belts as PPE for the purposes of this standard."
"OSHA has made it abundantly clear that they believe, based on a rigorous review of the science, that back belts are effective in reducing back injuries," said Huber. "Millions of back belt users would agree."
by Virginia Sutcliffe