The language used in consent forms for people volunteering to take part in medical experiments is too difficult for most people to understand, a survey has found.

Legally and ethically, participants in medical research trials must understand the nature of the procedure, its risks, benefits and alternatives. The information in the documents can be highly complex.

Researchers surveyed sample consent forms from 114 medical schools in the United States.

They found the average form was written at a Grade 10 reading level, while it is estimated that half of Americans read at or below an eighth-grade level.

Estimates of reading levels are based on the average number of syllables per word and the average number of words per sentence.

The medical schools' institutional review boards are responsible for safeguarding potential subjects. But the researchers found the forms provided by the boards generally failed to meet their own standards for reading comprehension.

Average readability scores for the sample texts provided by the boards exceeded the stated standards by almost three grade levels, the researchers found.

The U.S. Office for Human Research Protections oversees 52 of the medical schools. Forms from these schools tended to be easier to read.

Dr. Michael Paasche-Orlow of the department of medicine at Johns Hopkins University led the study, which appears in Thursday's issue of The New England Journal of Medicine.

"Our study suggests that a fourth- to sixth-grade reading level is a suitable target, because text at this level can best convey key concepts simply and directly," said Paasche-Orlow.

He also suggested using alternative ways of presenting the information, such as multimedia presentations.

Paasche-Orlow plans to revise some of the forms at his university and ask focus groups to test the improved language.