Saylor URL: http://www.saylor.org/books Saylor.org
measures) predicts many childhood and adult behaviors. Securely attached infants have closer, more harmonious
relationship with peers, are less anxious and aggressive, and are better able to understand others’ emotions than are
those who were categorized as insecure as infants (Lucas-Thompson & Clarke-Stewart, (2007). [35] And securely
attached adolescents also have more positive peer and romantic relationships than their less securely attached
counterparts (Carlson, Sroufe, & Egeland, 2004). [36]
Conducting longitudinal research is a very difficult task, but one that has substantial rewards. When the sample is
large enough and the time frame long enough, the potential findings of such a study can provide rich and important
information about how people change over time and the causes of those changes. The drawbacks of longitudinal
studies include the cost and the difficulty of finding a large sample that can be tracked accurately over time and the
time (many years) that it takes to get the data. In addition, because the results are delayed over an extended period,
the research questions posed at the beginning of the study may become less relevant over time as the research
continues.
Cross-sectional research designs represent an alternative to longitudinal designs. In a cross-
sectional research design, age comparisons are made between samples of different people at different ages at one
time. In one example, Jang, Livesley, and Vernon (1996) [37] studied two groups of identical and nonidentical
(fraternal) twins, one group in their 20s and the other group in their 50s, to determine the influence of genetics on
personality. They found that genetics played a more significant role in the older group of twins, suggesting that
genetics became more significant for personality in later adulthood.
Cross-sectional studies have a major advantage in that the scientist does not have to wait for years to pass to get
results. On the other hand, the interpretation of the results in a cross-sectional study is not as clear as those from a
longitudinal study, in which the same individuals are studied over time. Most important, the interpretations drawn
from cross-sectional studies may be confounded by cohort effects. Cohort effects refer to the possibility that
differences in cognition or behavior at two points in time may be caused by differences that are unrelated to the
changes in age. The differences might instead be due to environmental factors that affect an entire age group. For
instance, in the study by Jang, Livesley, and Vernon (1996) [38] that compared younger and older twins, cohort effects
might be a problem. The two groups of adults necessarily grew up in different time periods, and they may have been
differentially influenced by societal experiences, such as economic hardship, the presence of wars, or the introduction
of new technology. As a result, it is difficult in cross-sectional studies such as this one to determine whether the