The four signatories to this letter recently met with Plastics News on this subject, and we emphasized how important it is to carefully distinguish studies that purport to find "links" to harm from those which actually find causes. We thought your readers would benefit from the points we discussed, and from taking a closer look at how researchers look at risk to help put this study and others like it in perspective.

Scientists who study human health effects conduct many different types of research. Some research (like the study that was the subject of your article) is specifically designed to look for potential associations. Importantly, these associations don't provide answers, but they can provide clues for further research. In other words, this type of research helps scientists to ask new — and sometimes better — questions for further study.

Other types of research are designed to provide answers, and sometimes those answers can pinpoint the cause of a disease or

other health outcome. When scientists identify and evaluate potential causes, they look at many different factors to help evaluate the strength of their findings. Some of these include: consistency of findings (across multiple studies, different populations, and under different conditions), strength of association, biological mechanism and corresponding dose-response data, sample size and many other factors.

When it comes to determining whether or not a chemical exposure can cause disease, scientists also look at exposures (how much and how often a person comes into contact with a substance) and hazard (the properties of a substance that can trigger a negative health outcome) to determine a person's level of risk.

Identifying causal relationships is critical because it allows industry to take preventive actions. For example, where a potential risk has been established for chemical exposures, employees are required to wear personal protective equipment or take other actions to minimize risk. And where a risk of injury has been determined, corrective actions are promptly put in place.

Importantly, the study covered in your Nov. 26 article contained a number of critical limitations that precluded a determination of causality, some of which were clearly noted by the study's own authors. Perhaps most importantly, the study only examined occupations and did not look at exposures to any substances or potential agents.

While we wholeheartedly agree that investigations that help protect workers are a worthy and important area of research, it would be inappropriate to use the findings of this study to assert a causal relationship as it contained no information about the substances or agents present, actual exposures, or how large or frequent those exposures might have been.

The plastics industry is fully committed to protecting the health and safety of its workers. We invest significant time and resources in employee safety training and compliance with all applicable Occupational Safety and Health Administration standards, and we're proud of our record.

Through the industry's Responsible Care program, resin producers have some of the best safety records in all American manufacturing. And the plastics industry as a whole has a safety incidence rate that is 27 percent safer than all manufacturing. In addition, our industry is safer than passenger air transportation, urban bus travel, utilities, hospitals, and state and local government. And we are striving to do even better.

Just as our employees deserve the industry's commitment to safety, they also deserve safety information they can rely on. We hope Plastics News will continue to cover worker safety news in a scientific context that includes established risk factors and the limitations of a study — those stated by the authors and from other relevant voices. We also hope that your headlines and ledes will better capture some of these nuances to help your readers avoid any undue alarm.

And we hope that Plastics News readers will become more critical of what they read and understand that any study that claims to have found "links" should be viewed with a healthy dose of skepticism.

Steve Russell, vice president, plastics, American Chemistry Council

Bill Carteaux, president and CEO, Society of the Plastics Industry Inc.

Carol Hochu, president and CEO, Canadian Plastics Industry Association

Troy Nix, executive director, Manufacturers Association for Plastics Processors