The way schools, libraries, and parents apply filtering software to block pornographic and controversial web sites can have a “large impact” on students’ access to health-related information, according to a new study by health researchers.

The study found that filtering software set to a “moderately restrictive” blocking level—commonly found in schools and libraries—blocked three times as many health sites as the least restrictive setting.

While only 5 percent of more than 3,000 health sites were blocked in the study, the software blocked on average 27 percent of sites about condoms and 20 percent of sites about safe sex, an impact on web surfers that researchers described as “modest.”

“A teenager whose access to a particular health information site is inadvertently blocked will probably be able to … find an unblocked site with similar information,” said the study, which was published in the Dec. 11 issue of The Journal of the American Medical Association.

The study also found that software filters, which can be adjusted in intensity, can be fooled: They commonly block more internet sites associated with terms like “safe sex” or “condoms” than web pages a person might find while searching for information about “birth control” or “herpes.”

Researchers set out to determine whether internet filters inadvertently block access to useful health information, because teenagers increasingly rely on the internet for answers to health-related questions.

More than 70 percent of 15- to 17-year-olds say they have used the internet to look up health information such as cancer, diabetes, pregnancy, birth control, sexually transmitted diseases, or sexual assault. Teenagers without computers at home tend to rely on school and library computers for internet access, the study said.

Researchers tested software from six different companies—SmartFilter, 8e6 Technologies, Websense, SurfControl, Symantec, and N2H2—along with AOL Parental Controls. At least-aggressive levels, filtering software prevented researchers from viewing 1.4 percent of health sites surveyed and 9 percent of sites specifically about sexual health. The study’s supporters said that as the level of blocking increased, more health sites were blocked than additional pornography sites.

“The message is, a little filtering is probably OK,” said Victoria Rideout, a vice president at the Henry J. Kaiser Family Foundation, a philanthropic group that publishes some sexual health information on the web and sought to find out how much of its work was inaccessible to students and library patrons. Kaiser paid $200,000 for the study.

Congress in 2000 required internet filters in schools and libraries that accept federal funding, but a U.S. appeals panel in Philadelphia last year ruled that part of the Children’s Internet Protection Act (CIPA) violates the First Amendment because filters also can block sites on politics, health, and science. The appeals-panel ruling applied only to public libraries. CIPA would remain in force for schools, unless the ruling were expanded. The Supreme Court has said it will decide the issue by next summer.

While the study seems to say filters are doing an OK job, critics point out that it also found that filters aren’t foolproof.

“The Kaiser study demonstrates the reasons why it is both unwise and inappropriate to place reliance on filtering software to protect young people when they are using the internet,” said Nancy Willard, a research associate at the University of Oregon’s Center for Advanced Technology in Education.

“In those categories where the subject area is controversial or the sites themselves may contain controversial information, the rate of overblocking was significantly higher. The categories that stood out included safe sex, homosexuality, and drugs,” Willard said.

At most-restrictive levels, designed to block access to racism, hateful speech, or sites about violence or gambling, filtering software blocked 24 percent of health sites and 50 percent of sites specifically about sexual health, the study found.

In the least restrictive category, Websense was least likely to block health information, and N2H2 was a close second, the researchers said.

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Henry J. Kaiser Family Foundation http://www.kff.org