In psychology, correlational research determines if a relationship exists between two or more variables, and if so, to what degree the relationship occurs. There are three main types of correlational studies: natural observation, survey research, and archival research.
Descriptive research methods are pretty much as they sound — they describe situations. They do not make accurate predictions, and they do not determine cause and effect. There are three main types of descriptive methods: observational methods, case-study methods and survey methods.
Experimental psychology was introduced into the United States by George Trumbull Ladd, who founded Yale University's psychological laboratory in 1879. In 1887, Ladd published Elements of Physiological Psychology, the first American textbook that extensively discussed experimental psychology.
A key debate, is the one between the two research methods: nomothetic and idiographic. The debate concerns which method of enquiry is more important and which would allow greater and more valid investigation into the field of psychology. Nomothetic research is about attempting to establish general laws and generalisations.
From these examples we can see that the difference between a nomothetic and an idiographic approach is not just a question of what the psychologist wants to discover but also of the methods used. Experiments. correlation, psychometric testing and other quantitative methods are favoured from a nomothetic point of view.
Scientific research in psychology can be ethical only if its risks are outweighed by its benefits. Among the risks to research participants are that a treatment might fail to help or even be harmful, a procedure might result in physical or psychological harm, and their right to privacy might be violated.
Data from these questionnaire can be used to identify relationships between scores on the variable(s) that the questionnaire is assumed to measure and either performance on behavioural tasks, physiological measures taken during an experiment, or even scores obtained from other questionnaires (some studies just report on the correlations between batches of self-report measures!).
Psychological statistics is application of formulas, theorems, numbers and laws to psychology. Statistical Methods for psychology include development and application statistical theory and methods for modeling psychological data. These methods include psychometrics, Factor analysis, Experimental Designs, Multivariate Behavioral Research.