In a study released Tuesday, researchers determined that children who were spanked as 1-year-olds were more likely to behave aggressively at age 2. How do you measure the aggression of a 2-year-old?
Ask the parents. Psychologists send out a standard questionnaire, called the Child Behavior Checklist (PDF), which uses 100 descriptive phrases to rate a toddler's actions over the past two months. These include acts of violence—like "Hits others" and "Cruel to animals"—and more inwardly focused behaviors—like "Uncooperative" and "Plays with own sex parts too much." Parents mark down 0, 1, or 2 for each phrase, depending on how well it applies to their kid. Then researchers add up the values for a specific subset of the items—usually 15 or 20—to create an index of toddler aggression. The most peaceful tot would score a zero; the most feisty, a 30 or 40.
There's some controversy over which behaviors on the checklist should be counted toward "aggression." For example, the standard set counts temper tantrums—which may or may not include acts of violence—alongside, say, throwing a cat against the wall. Since there's no weighting of one item against another, these two behaviors would contribute equally to a toddler's measured aggression. Opponents of the index say it may invite laypeople to assume that poor and Hispanic toddlers—who tend to score higher in aggression than other kids—are especially violent.
The checklist can be used to measure large groups of children quickly and without too much expense. (There were 2,573 child subjects in the study published Tuesday.) It also allows toddlers to be observed and assessed at home, rather than in the unnatural environment of a behavior laboratory. But not every parent will respond to the questionnaire in the same way. Parents who spank, for example, may be more likely to view their child as being aggressive (and thus deserving of corporal punishment).
For smaller studies of toddler aggression, researchers often try to observe the child directly and videotape the session for later review. They'll put the child in a room with a parent or some peers and then create a provocative situation—a limited number of toys, perhaps, or an inattentive parent. Then the observers make a note whenever the child engages in an aggressive behavior—like screaming at someone, throwing a punch, or kicking the wall. Each session is broken down into time intervals of about 10 seconds each, and the acts of aggression are divided up according to the times when they occurred. Then overall scores are tallied in two ways—as the amount of time that elapsed before the child's first aggressive act and as the percentage of time intervals during which the child was riled up.
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Explainer thanks Lisa Berlin of Duke University and Daniel S. Shaw of the University of Pittsburgh.