More surprisingly, the results showed that scientists feel most affected by informal constraints.
"These are rules that are not written," Kempner said. "They may be ideas that researchers say that everyone kind of knows about."
Such constraints include the threat of social sanction. Scientists may stay away from research not because it's illegal, but because it breaches an unspoken rule about what is appropriate to study and what is not.
"There may be things that researchers think they can't do, because they anticipate some kind of threat," Kempner said.
Some scientists, though, may seek out controversial topics.
"Forbidden doesn't mean it's never done," Kempner said. "No matter what the topic, there will probably always be somebody who is willing to do the research."
Forty-two percent of the scientists interviewed said their own work had been targeted for censure.
Repressing Today's Kinseys?
One of the most controversial fields is sex research.
For example, activists accused one researcher in Kempner's study of "murderous behavior," because he did not report HIV-positive subjects who admitted to unsafe sex practices in an anonymous survey.
Sex researchers say they are feeling the heat of a politically conservative crusade mounting against them, making their work more difficult.
As a result, some people may choose not to get into sex research, said Bill Yarber. Yarber is a professor in applied health science and gender studies at Indiana University in Bloomington, where pioneering and controversial sexologist Alfred Kinsey practiced in the mid-20th century.
"If a person needs complete social approval for what they're doing in academics, this [field] is not it."
In 2003 the U.S. Congress threatened to withdraw government funding of several sex studies.
"We are continuously confronted with the controversy surrounding this type of research, and we are often the target of it," said Erick Janssen, a research scientist at Indiana University's Kinsey Institute for Research for Sex, Gender, and Reproduction.
Janssen's grant from the U.S. National Institutes of Health to study the role of mood and sexual arousal in people's sexual decision-making was one of the grants attacked in Congress.
Many researchers say they have to couch the language of their studies to avoid controversy and secure funding.
Kempner said the topics that are "forbidden" are strongly tied to culture and era.
"[Some] DNA research was controversial in the 1970s but is accepted now," she said. "The idea of what can and can't be done changes with time."
But while formal constraints, such as government laws may be relatively transparent and easy to change, informal constraints may be harder to define and may be culturally ingrained.
"This is affecting scientific agendas, and it's important to figure out whether there are things that aren't being studied that really should be studied," Kempner said.
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