The study of development is that of changes in physical, cognitive, social and emotional capabilities over time. The study is usually carried out on infants and children as their changes are faster and more dramatic than adults. These time based studies reveal that the data collected shows the abilities of subjects and the ages they appear. The data is collected through interviews, observations, tests and desk research of older studies. These interviews, observations and tests are usually carried out one of two ways.
The cross-sectional approach to research entails the study of two or more groups of similar ages. The groups are tested and their capabilities compared to evaluate development (the difference of skills). In the longitudinal approach there is one study group, or one main age group which is studied for a certain amount of time or until they develop appropriately, and their progress is then interpreted and noted.
Cross-sectional studies are preferred for short term studies that may have immediate social effects and need to be proven as soon as possible. For example the effect of day cares as opposed to parent supervision of the child. The short term nature of the study is because the information can be taken from several study groups at once and there is no need to wait for the members of any group to reach the tested age. Information collected in one session could take years to collect in a longitudinal study.
This brevity also means the studies are relatively cheap to carry out, thus people will more likely fund cheaper studies and so theorists will be more able to test their hypothesises, that is, easier funding means the possibility of carrying out more tests!
From the subject's point of view most people are less likely to mind a brief or "one-off" interruption in their or their children's life. This means that bigger pools of...