Longitudinal approach to the study of development implies repeated observations of phenomena during some time with the object of revealing constant aspects and changes, and also with the object of their explanation.
Longitudinal method is a special kind of observation. Its task is to determine causes of inward individual changes that happen to one person, or to different individuals or to various groups of people.
This approach is considered to be the ideal one for development psychology which can be defined as a science that studies changes that happen in human’ s behavior depending on his age.
The usage of the longitudinal method was closely connected with the growth of development psychology. Indeed, there are a lot of biographies and journals where children’s behavior is described in the process of their development. The longitudinal method was widely used from 1916, when testology appeared.
In order to receive data with the help of longitudinal approach some tests, questionnaires, observation method are used. Time distance between longitudinal measurements depends on the period of life that is investigated. For instance, for an adult person a week is a very short period of time, while for an infant a week is a very considerable period.
Advantages of longitudinal approach:
1. Longitudinal method explains changes that happen according to age. Longitudinal method consists in observation or measurement of the same examinees. They are conducted during certain time. That’s why attention is paid to changes that happen inside of the individual, but not to changes that occur between different individuals.
2. This approach admits the comparison with other examinees.
3. Longitudinal approach allows to compare changes that happen under various external circumstances.
4. Higher accuracy in prognosis of psychic development of a certain person and of future process of psychic evolution in general (in comparison with cross-sectional approach).
5. Longitudinal method gives the opportunity of defining genetic connections between phases of psychic development. It also allows to establish the diapason of fluctuations of age norms and the moments of transformation one phase into another.
6. Longitudinal method takes into account individual social, psychological and psychophysiological peculiarities of a person.
Using of longitudinal method gives the opportunity of defining the curve of child development and to determine whether his development correspond age norm. This method allows to reveal turning-points in this curve when sharp qualitative changes occur.
Longitudinal method is not free from shortcomings. It does not give the opportunity of penetrating into phenomena, of understanding the mechanism of psychic processes. The facts received by this method can be explained only by various hypotheses. There is no necessary accuracy of their interpretation.
Disadvantages of longitudinal method:
1. Time. It requires much time to finish the investigation.
2. Siftings. It can happen that some examinees will quit the instigation or it will not be possible to find them.
3. Repetition of trials. The matter is that something can happen that will bring down the validity of investigation. For example, examinees can learn the answers or can guess experimenter’s goals and they start to play “good” examinee.
4. Outdated theoretical and methodological base, that was used at the beginning of investigation.
5. Equivalence of tests that are used, if they are repeated several times.
6. Labor-intensiveness of organization and carrying out of longitudinal method. It is very important for receiving reliable data to determine definite duration of the whole investigation. Besides it is essential to define the quantity and periodicity of carrying out the control measurements. It is known that the longer longitudinal investigation is, the higher reliability of results is. But at the same time investigators want the longitudinal research does not exceed the bounds of their life.
7. There are some difficulties connected with the demands to methods. The matter is that for conducting longitudinal investigation the parallel series of methods are needed. But it takes mush time to work out them. Otherwise the results will be conditioned not by changes in person’s psychic organization, bur by person’s adaptation to tests and training.
8. There should be paid much attention to the quantity of examinees. From the one hand a small quantity of chosen examinees make it difficult to reveal age peculiarities. From the other hand long – term investigations are accompanied by reduction of participants because of their diseases, removals, death.
The hypothesis of longitudinal method consists of the suggestion that person’s development is determined by his age, by biological causes, individual and historical events and by conditions of the surroundings.
Cross-sectional approach is the alternative method to longitudinal method. This method implies the comparison of different groups of people according to their age, education, activity work and communication. The main task of cross-sectional approach is to compare examinees of different age. This comparison can be more useful in case that longitudinal comparison of a small quantity of examinees was already carried out.
Originally, cross-sectional approach was used for studying the phylogenesis of behavior and psychic activity. Nowadays it is widely used in development psychology and it covers a lot of grounds, namely:
• Various level of development, for example, comparison psychic organization of a human being and primates.
• Various periods of development, for instance the comparison children of pre – school age with children of school age.
• Different phases of the same period. For example, the comparison psychic organization of people of early and of late adulthood.
Besides this criterion of age, there are some other ones, such as: investigations revealing psychic peculiarities according to age, to professional belonging, state of health and so on.
There are some advantages of cross-sectional approach:
1. The usage of cross-sectional method to carry out quite extensive investigations for a short period.
2. It allows to cover various age categories and to reveal a lot of determinates.
3. Cross-sectional method gives the opportunity to retrace the dynamics of age development, succession of different phases and periods of formation of psyche.
4. Moreover it permits to reveal evolution characteristics of the dynamics of psychic formations that are studied under the identical social, cultural, historical and economic circumstances.
5. Cross-sectional method allows to conduct the comparison of people of different age for a short time.
There are also some disadvantages of cross-sectional approach, namely:
1. There are some limitations in application of cross-sectional method, that are connected with underestimation of the role of individual variability of psychic manifestations when studying general processes.
2. Cross-sectional method is characterized by levelling individual, social, psychic, physioligic peculiarities and be equalization of all examinees of the same age and belonging to one group.
3. The problem is that cross-sectional method presupposes the creation of equivalent groups according to many factors, such as sex, education, social level and others. But as a rule examinees belong to different cohorts, that’s way they undoubtedly have various experience.
The investigations with the help of cross-sectional method consist in the following:
• The groups for investigation are chosen. They should differ one from another according to the given criterion. It can be definite social, psychological, physical factors.
• Necessary psychodiagnostic methods are chosen.
• The same methods are proposed to the groups that take part in the investigation.
Sometimes these two methods are opposed to each other. But it is not quite correct. The comparison is used in both of them but in one case facts about different objects are compared, and in other case fact about one object are compared during all his development.
But nevertheless the opposition is quite rightful. As each method has its pros and cons. If cross-sectional method allows to cover more people, longitudinal method allows to discover different tinges of individual development, that are elusive for cross-sectional method. These methods practically are considered to be mutually complementary.
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