The central objective of Naerde, Ogden, Janson & Zacharisson’s 2014 study, Normative Development of Physical Aggression (PA), was to expand the amount of research in the literature on physical aggression in infants and toddlers. The major research question was, “What is the normative development of physical aggression in children ranging from 8-26 months?” However, in addition to the key question, they also asked the following: “How does PA develop across this age period?”, “Do children vary in terms of level and developmental change of PA and are there gender differences?”, and “Do family, parental, and child characteristics predict level of PA and/or developmental change over time?” (Naerde, Ogden, Janson & Zacharisson, 2014)
In the study, the authors hypothesized numerous things. First, they assumed that as age increases (up to two), so does physical aggression. They also expected variability among the children when looking for their degrees of change. In addition, non-substantial gender-differences were anticipated to be present in boy and girl infants, but as boys become older, the differences were expected to become more substantial. Furthermore, based on other’s findings in the literature, physical aggression was predicted to escalate when children are of a higher sociodemographic risk or have mentally-distressed parents. Finally, the researchers looked at if certain combinations of these factors resulted in higher rates of physical aggression. (Naerde et al., 2014)
The participants in this study were 559 girls and 600 boys for a total of 1159 children. These kids were all from five municipalities in the southeast region on Norway. The data in this study was originally from a longitudinal study based on population called the Behavioral Outlook Norwegian Development Study (BONDS) which was directed by the Norwegian Center for Child Behavioral Development. The participants were found at their five-month checkups in the years 2006-2008. In order for a child to participate, he or she must have been of the correct age and had at least one parent willing to cooperate with reporting the results. (Naerde et al., 2014)
The research was conducted through the use of personal interviews at 6, 12, and 24 months. Both the mother and father were asked to be involved in the first interview, but mainly fathers were invited to the 12-month interview and mothers to the 24-month interview. These interviews not only had a speaking part, but a questionnaire on a computer as well. In order to maximize information pertaining to the children, shorter, less-extensive phone interviews were also given 2 and 1 month prior, 8, 10, 12, 14, 16, 18, 20, and 22 months, and 1, 2, and 3 months after children were placed in center-based child-care. (Naerde et al., 2014)
The designs of measurement used were the multiple measurements per child over time, the maximum number of PA items, and Rach scaling. Both telephone and personal interviews were comprised of a range of 2-9 PA items when dealing with kids 10 months or older. Many clinicians consider ‘Hits you’, ‘hits sibling’, and ‘pushes someone to get his/her will’ to be the three PA items to only be pertinent to infants 12 months and older. However, in this study, they were completed at all ages. “Bites someone”, when unrelated to breastfeeding, was also completed from 12 months on. The next two things were completed from 18 months onward, “throws things at others” and “kicks someone.” Finally, the last three items, “hits other adults”, “pulls hair” and “pinches someone” were completed in the questionnaire at 24 months exclusively. The reason this list of items on PA is so unique is that it isn’t an alteration of a previously used set. Rather, it is an original tool with fluent wording that a parent can understand enough to report accurately. (Naerde et al., 2014)
The results of this study confirm the idea that the development of physical aggression is not linear. Instead, they point to an increase in PA at 20-26 months and a decrease in PA around 26 months. Most of the authors’ hypotheses were supported. Same-age-siblings, maternal and paternal mental distress, and problematic child temperament all were related to higher levels of physical aggression. Gender was only trend-significant. (Naerde et al., 2014)
Limitations of this study, as mentioned by the authors, did exist like in most every study. First, the fact that parents were reporting the information is an extremely non-objective and biased way to collect information. Second, physical aggression is only reported up until the age of twenty-six months which is denying the possibility of discovery in later months. Third, all of the predictors used at the six-month mark were time-invariant. This denied the possibility of finding time-varying predictors as the child grows past six months. The authors did not describe any future research suggestions. (Naerde et al., 2014)
The study was conducted somewhat effectively. The sample was slightly biased towards moms who had more education, less parents who immigrated, more firstborn children, and a lesser number of single mothers. So, overall, the sample was only slightly representative of most 8-26 month olds. The study didn’t really mention any confounding variables so, in turn, they didn’t need to control any of them. (Naerde et al., 2014)
The measures were not the most reliable due to their parent-reported nature. The measurement of the list of items that was used was quite unique and was a completely original system because it had not been modified from another system. (Naerde et al., 2014) An extraneous confounding variable that may have influenced the findings is the bias of the parents. If the mother, for example, wanted her child to be thought of as having better behavior than they actually do, she may report incorrect information in order to influence or improve the reputation of the child and/or the parenting skills of she and her spouse. The author’s conclusions did make sense based on the data. The in-depth and numerous reports about each specific child helped to further and concrete the evidence supporting their hypotheses. (Naerde et al., 2014)
One limitation that the author failed to mention is that mothers only were invited to the interviews at 24 months and fathers only were invited to the interviews at 12 months. The reason that this limits the study is this: Oftentimes, men and women have different perspectives on situations, especially concerning children, and only utilizing one parent at the 12 and 24 months interviews could have easily skewed or even damaged the data. (Naerde et al., 2014)
The findings are actually very generalizable because of the size of the sample and the general parallels in most infants. Most babies hit developmental milestones at very similar time frames. This means they would experience physical aggression typically around the same times.
A future research study that could build on these current findings and be a beneficial addition to the literature would be a study investigating if a causation exists between maternal habits such as smoking and increased physical aggression in toddlers. Is there a genetic component to physical aggression? Could it be improved by refining the mother’s behavior into better habits?
This article was such an advantageous add-on to the literature regarding infant and toddler physical aggression because of the fact that little to no research existed on this particular age group (8-26 months). It would certainly be beneficial for parents to look into this research in order to understand and teach their kids more effectively. Overall, this study was highly informative, significant, and a great steeping stone for much of the research to come regarding physical aggression in children.
