填空题

Questions 47 to 51 are based on the following passage.
Recently a sociologist from the University of New Hampshire, Murray Straus, presented a paper suggesting that corporal punishment leaves a long-lasting mark—in the form of lower IQ. Straus found that kids who were physically punished had up to a five-point lower IQ score than kids who weren’t—the more children were spanked, the lower their IQ—and that the effect could be seen not only in individual children, but across entire nations. Straus found that countries with higher GDP tended to be those where corporal punishment was used less often. In the U. S., the tendency to hit also varies with income, geography and culture.
So how might getting spanked on the butt actually affect the workings of the brain Straus notes that being spanked or hit is associated with fright and stress; kids who experience that kind of trauma (创伤)have a harder time focusing and learning.
It’s not clear if spanking causes lower cognitive ability or if lower cognitive ability might somehow lead to more spanking. It’s quite possible that kids with poor reasoning skills misbehave more often and therefore elicit harsher punishment. "It could be that lower IQ causes parents to get angry and hit more," Straus says, "I believe the relationship is probably bidirectional," "There has to be something the kid is doing that’s wrong that leads to corporal punishment. The problem is, when the parent does that, it seems to have counterproductive results to cognitive ability in the long term." says Straus.
One problem with Straus’data is that some of the parents who tended to spank may also have been engaging in actual physical abuse of their children. Researchers define corporal punishment as physical force intended to cause pain—but not injury—for the purpose of correcting a child’s behavior, not simply hurting him. Studies have shown that very few parents who use corporal punishment also beat their kids, but Straus can’t rule out the possibility that his data is confounded by the presence of child abuse, which past research has shown to affect victims’ development.
The practice has its defenders. In the 1990s, the American Academy of Pediatrics underwent a bitter fight before finally declaring in 1998 that "corporal punishment is of limited effectiveness and has potentially deleterious side effects." Sometimes spanking seems like the only way to get through to an unruly toddler. But the price for fixing his poor short-term conduct might be an even more troublesome outcome in the future.
Straus believes that the relationship between punishment and IQ is probably ______.