What is the central idea of the passage?

Directions: Answer the given question based on the following passage:

Data of educational psychology are obtained in various methods. These methods range in reliability from extremely low to very high. In addition to the questionable validity of the information obtained by research, there are certain risks of inference involved when the results of laboratory investigations are extrapolated to classroom applications. Every classroom is unique in many ways and there are certain risks in generalising from the laboratory to the classroom as well as from one type of classroom to another.
Educational psychologists and educators in the field would do a service to the profession if they would cross-validate laboratory studies in the classroom and pool the results from such studies in several schools to determine the generality of their findings.
Conventional textbooks are quite unsatisfactory for the student who wishes to critically evaluate the reliability of the methods used in obtaining the information presented. The book, which presents enough of the methodology of the studies from which all of the data presented are derived, would be able to cover a very limited area of subject matter and a small number of studies. It is necessary, therefore, for textbooks to become authoritarian in tenor and subject-matter oriented if they are to be useful to the student who is largely a consumer of research data. Data presented in textbook fashion must be accepted largely on faith—faith in the veracity of the presentations and in the reliability of the research methods used.
The student who is critical will want to go back to the original studies to check on the original methods and data on issues which are crucial for him. There are books of readings available in which selected studies are presented in their complete forms. These constitute useful supplements to the subject-matter oriented textbook. A textbook should be perceived by the student as a presentation of the best available information to date, organised and interpreted within a limited frame of reference.