Objectives

Examine trends in aggressive behavior from 1991 to 2015, investigate whether these trends apply equally to all individuals, and explore the extent to which differences in trends over time cluster within families.

Methods

Our study included 69,465 measures from 40,400 individuals, from 15,437 Dutch families. Aggression was measured between 1 and 4 times by self-report. We fitted a mixed effects model, modeling the effect of time, age, and gender on aggression, and considering the three levels of nesting in the data, i.e. repeated measures, individuals, and families. To investigate if individual differences in trends in aggression over time cluster within families, variance in aggression and in time and age effects was partitioned into within- and between family variance components.

Results

We found a steady decline in aggression over time, between 1991 and 2015, as well as over the life course. Across time and age, women had slightly higher levels of aggression than men. There was clear evidence for clustering within, and variation between families, both in overall aggression levels and in time effects.

Conclusions

We confirm earlier findings of a decline in aggression over the past decades. Not all individuals follow the downward trend over time for aggression to the same extent. Trends over time cluster within families, demonstrating that family factors are not only important to explain variation in aggression levels, but also in understanding differences between individuals in time trends.

中文翻译：

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侵略趋势的家族聚类

目标

检查 1991 年至 2015 年攻击行为的趋势，调查这些趋势是否同样适用于所有个人，并探索随时间推移的趋势差异在家庭内聚集的程度。

方法

我们的研究包括来自 15,437 个荷兰家庭的 40,400 个人的 69,465 项措施。通过自我报告测量了 1 到 4 次攻击性。我们拟合了一个混合效应模型，模拟了时间、年龄和性别对攻击性的影响，并考虑了数据中嵌套的三个层次，即重复测量、个人和家庭。为了调查攻击性趋势随时间的个体差异是否在家庭内聚集，攻击性的差异以及时间和年龄效应被划分为家庭内部和家庭之间的差异分量。

结果

我们发现，从 1991 年到 2015 年，以及在整个生命过程中，攻击性都在稳步下降。随着时间和年龄的变化，女性的攻击性水平略高于男性。有明确的证据表明家庭内部的聚集和家庭之间的差异，无论是在总体攻击水平还是时间效应方面。

结论

我们证实了过去几十年侵略性下降的早期发现。并非所有个体的攻击性都随着时间的推移而呈下降趋势。家庭内随时间推移的趋势聚集，表明家庭因素不仅对于解释攻击水平的变化很重要，而且对于理解时间趋势中个体之间的差异也很重要。