Life Span and Developmental Psychology Scientists use three main research designs to study human lifespan development; longitudinal, cross sectional and sequential designs. The longitudinal design involves the study of selected participants repeatedly over a given span of time. This can be over a short time ranging from a few months to a few years, or can be over a long period of time spanning to a decade or more. The advantage that the researchers have in using this approach is that they are able to observe common patterns among the participants as well as differing trends among them in the early as well as late events in their lives. On the other hand, the weaknesses that it has are that there is possibility of distortion of the age related changes occasioned by participants dropping out, the cohort effects and practice effects in the process of the research.

Cross-sectional design is when the researcher engages in studying different groups of participants who are of different ages at the same given point in time. Since the study is done once at the chosen time, it is not affected by the participant dropouts and also not subject to the practice effect. The challenge with this approach however is one cannot study the individual participant's developmental...

The advantage of this approach is that it allows for the longitudinal and cross-sectional comparisons as well as gives the researcher that easy time in identifying and eliminating the cohort effects. The challenges that may be experienced may be similar to those in the longitudinal and cross sectional above, though this approach will help identify these challenges.
Methods of human behavior observation and reporting

The systemic observation involves the researcher set out to study human behavior going to the natural environment of the subject and observing their behavior as they interact with their environment as naturally as it was before the research began. This method provides critical data as the researcher observes the participants, however, it cannot give the researcher the insight into why the children or elders behave as they do. This then calls for the self-report method which involves asking…