On psychological data collection methods

Organizational Methods
The knowledge of the patterns of mental development can be approached through two main types of research: the so-called transverse sections and longitudinal (longitudinal). Both types have a number of advantages and disadvantages.
Cross-sectional studies of mental development consist in studying the same psychological characteristics in groups of children of different ages, different levels of development, with different personality traits, clinical reactions, etc. The cross-sectional method also has its advantages and disadvantages. The main advantage of this method is the comparative speed of the study - the possibility of acquiring results within a short time.
However, studies in purely transverse sections are static and do not show the dynamics of the development process, its continuity, and many patterns of development obtained in this way are very approximate.
Modern longitudinal studies aim to record the somatic and mental development of the child. Many specialists, children's doctors and psychologists (Stern, Buhler, Menchinskaya, and others) devoted themselves to long-term observation of their own children. The 1930s brought significant progress in the study of development. Valuable are the observations of young children carried out by Gesell's laboratory (carried out for a whole day). Gesell also studied a group of children month by month, and on the basis of his observations he deduced "norms for the development of behavior" for different age levels, ranging from 0 to 16 years.
In our country, ontogenetic research has a long tradition (V.M.Bekhterev, N.M. Shchelovanov, L.S.Vygotsky, A.N.Leontiev, D.B.Elkonin, A.A. Lyublinskaya, N.D. Levitov and others). Particularly well-known are studies of the development of speech and its influence on the ability to learn and develop the personality of children, conducted in the laboratory of A.R. Luria (1959, 1961).
R. Gotgshaldt (1960) conducted longitudinal psychological research on twins for more than 20 years. In France, René Zazzo dealt with the same problem. Gemini is a particularly suitable model for studying the influence of constitutional and social factors. This problem directly requires the use of a longitudinal study of twins, called the twin method.
The longitudinal method, in comparison with the method of transverse sections, has many advantages:

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  a longitudinal study allows processing data for individual age periods;
  
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  it makes it possible to determine the dynamics of the development of each child;
  
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  only a longitudinal study makes it possible to resolve the issue of the so-called critical periods in development.
  

However, it is obvious that even objective observation of one child does not allow us to come to a conclusion with universal significance. The main disadvantage of longitudinal studies is the significant time required to organize and conduct them.
The comparative method consists in considering individual mechanisms of behavior and psychological acts in comparison with similar phenomena in other organisms. This method is most widely used in zoopsychology and child psychology. This method is called "comparative genetic". The most productive use of this method in the field of comparative psychology (zoopsychology) belonged to V.A. Wagner. In his works, he was the first to substantiate and use the evolutionary method, the essence of which is to compare the psyche of the studied animal with representatives of the previous and subsequent stages of evolution of the animal world. For example, using the comparative method, it was found that chickens are not capable of extrapolation thinking, but dogs are.