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Psychology (Greek: ''Ψυχολογία'', lit. ''study of the mind'', from grc ''ψυχή'' psykhē ''breath, spirit, soul''; and grc -λογία, ''-logia'' ''study of'') is an academic and applied discipline involving the systematic, and often scientific, study of human mental functions and behavior. Occasionally, in addition or opposition to employing the scientific method, it also relies on symbolic interpretation and critical analysis, although it often does so less prominently than other social sciences such as sociology. Psychologists study such phenomena as perception, cognition, emotion, personality, behavior and interpersonal relationships. Some, especially depth psychologists, also study the unconscious mind.

Psychological knowledge is applied to various spheres of human activity, including issues related to everyday life—such as family, education and employment—and to the treatment of mental health problems. Psychologists attempt to understand the role of mental functions in individual and social behavior, while also exploring the underlying physiological and neurological processes. Psychology includes many sub-fields of study and applications concerned with such areas as human development, sports, health, industry, media and law. Psychology incorporates research from the natural sciences, social sciences and humanities. A professional theorist or practitioner of psychology is called a psychologist.

History

Philosophical and scientific roots

The study of psychology in philosophical context dates back to the ancient civilizations of Egypt, Greece, China, India, and Persia. Psychology began adopting a more clinical and experimental psychology as an independent experimental field of study began in 1879, when Wilhelm Wundt founded the first laboratory dedicated exclusively to psychological research at Leipzig University in Germany, for which Wundt is known as the ''father of psychology''. The year 1879 is thus sometimes regarded as the ''birthdate'' of psychology. The American philosopher William James published his seminal book, ''Principles of Psychology'' in 1890, laying the foundations for many of the questions on which psychologists would focus for years to come. Other important early contributors to the field include Hermann Ebbinghaus (1850–1909), a pioneer in the experimental study of memory at the University of Berlin; and the Russian physiologist Ivan Pavlov (1849–1936) who investigated the learning process now referred to as classical conditioning.

Psychoanalysis

From the 1890s until his death in 1939, the Austrian physician Sigmund Freud developed a method of psychotherapy known as psychoanalysis. Freud's understanding of the mind was largely based on interpretive methods, introspection and clinical observations, and was focused in particular on resolving unconscious conflict, mental distress and psychopathology. Freud's theories became very well-known, largely because they tackled subjects such as sexuality, repression, and the unconscious mind as general aspects of psychological development. These were largely considered taboo subjects at the time, and Freud provided a catalyst for them to be openly discussed in polite society. Clinically, he helped to pioneer the method of free association and a therapeutic interest in dreams.

Freud had a significant influence on Swiss psychiatrist Carl Jung, whose analytical psychology became an alternative form of depth psychology. Other well-known psychoanalytic thinkers of the mid-twentieth century included Sigmund Freud's daughter, psychoanalyst Anna Freud; German-American psychologist Erik Erickson, Austrian-British psychoanalyst Melanie Klein, English psychoanalyst and physician D. W. Winnicott, German psychologist Karen Horney, German-born psychologist and philosopher Erich Fromm, and English psychiatrist John Bowlby. Contemporary psychoanalysis comprises diverse schools of thought, most of which may be classed as Neo-Freudian.

Psychoanalysis was criticized by psychologists such as B. F. Skinner and Hans Eysenck, and by philosophers including Karl Popper. Skinner and other behaviorists believed that psychology should be more empirical and efficient than psychoanalysis, although they frequently agreed with Freud in ways that are overlooked today. Popper argued that Freud's psychoanalytic theories were presented in irrefutable, and therefore scientifically untestable, form, whereas Eysenck maintained that although Freudian ideas could be subjected to experimental science, they had not withstood experimental tests. Psychology departments in American universities today are experimentally oriented, and have marginalized Freudian theory, regarding it as a ''desiccated and dead'' historical artifact, according to a recent APA study. Recently, however, researchers in the emerging field of neuro-psychoanalysis have defended some of Freud's ideas on scientific grounds.

Behaviorism

Founded in the early 20th century by American psychologist John B. Watson, behaviorism was embraced and extended by Americans Edward Thorndike, Clark L. Hull, Edward C. Tolman, and later B. F. Skinner. Behaviorism reflected a belief that the methodology behind laboratory-based animal experimentation, which was increasing in popularity as physiology grew more sophisticated, could provide useful psychosocial understanding of a type that comparatively subjective inquiries, such as psychodynamic analysis as employed by Freud or introspection as used by Wundt and James, could not.

The behaviorists shared with their predecessors a philosophical inclination toward positivism and determinism. But Skinner's behaviorism has not died, perhaps in part because it has generated successful practical applications. Existential psychologists emphasized the humanistic themes of death, free will, and meaning, suggesting that meaning can be shaped by myths, or narrative patterns, and that it can be encouraged by an acceptance of the free will requisite to an authentic, albeit often anxious, regard for death and other future prospects. Austrian existential psychiatrist and Holocaust survivor Viktor Frankl drew evidence of meaning's therapeutic power from reflections garnered from his own internment, and he created a variety of existential psychotherapy called logotherapy. In addition to May and Frankl, Swiss psychoanalyst Ludwig Binswanger and American psychologist George Kelly may be said to belong to the existential school.

Cognitivism

Noam Chomsky helped to ignite a cognitive revolution in psychology when he criticized the behaviorists' notions of 'stimulus', 'response' and 'reinforcement', arguing that such ideas—which Skinner had borrowed from animal experiments in the laboratory—could be applied to complex human behavior, such as language acquisition, in only a vague and superficial manner. Chomsky emphasized that research and analysis must not ignore the innate contribution of the child to such behavior, while social learning theorists such as Albert Bandura argued that the child's environment could make contributions of its own to the behaviors of an observant subject. The notion that behavior could be precipitated only by the functioning of an internal device or by the perception of external surroundings posed a challenge to the behaviorist position that behavior is contingent upon the prior associations that individuals have made between behavioral responses and pleasurable or painful stimuli.

Meanwhile, accumulating technology helped to renew interest and belief in the mental states and representations—i.e., the cognition—that had fallen out of favor with behaviorists. English neuroscientist Charles Sherrington and Canadian psychologist Donald O. Hebb used experimental methods to link psychological phenomena with the structure and function of the brain. With the rise of computer science and artificial intelligence, analogies were drawn between the processing of information by humans and information processing by machines. Research in cognition had proven practical since World War II, when it aided in the understanding of weapons operation. By the late 20th century, though, cognitivism had become the dominant paradigm of mainstream psycholology, and cognitive psychology emerged as a popular branch.

Assuming both that the covert mind should be studied and that the scientific method should be used to study it, cognitive psychologists set such concepts as ''subliminal processing'' and ''implicit memory'' in place of the psychoanalytic ''unconscious mind'' or the behavioristic ''contingency-shaped behaviors''. Elements of behaviorism and cognitive psychology were synthesized to form the basis of cognitive behavioral therapy, a widely-used psychotherapy modified from techniques developed by American psychologist Albert Ellis and American psychiatrist Aaron T. Beck. Cognitive psychology was subsumed along with other disciplines, such as philosophy of mind, computer science, and neuroscience, under the umbrella discipline of cognitive science.

Schools of thought

Various schools of thought have argued for a particular model to be used as a guiding theory by which all, or the majority, of human behavior can be explained. The popularity of these has waxed and waned over time. Some psychologists may think of themselves as adherents to a particular school of thought and reject the others, although most consider each as an approach to understanding the mind, and not necessarily as mutually exclusive theories. On the basis of Tinbergen's four questions a framework of reference of all fields of psychological research can be established (including anthropological research and humanities).

In modern times, psychology has adopted an integrated perspective towards understanding consciousness, behavior, and social interaction. This perspective is commonly referred to as the biopsychosocial approach. The basic tenet of the biopsychosocial model is that any given behavior or mental process affects and is affected by dynamically interrelated biological, psychological, and social factors.

The ''psychological'' aspect refers to the role that cognition and emotions play in any given psychological phenomenon—for example, the effect of mood or beliefs and expectations on an individual's reactions to an event. The ''biological'' aspect refers to the role of biological factors in psychological phenomena—for example, the effect of the prenatal environment on brain development and cognitive abilities, or the influence of genes on individual dispositions. The ''socio-cultural'' aspect refers to the role that social and cultural environments play in a given psychological phenomenon—for example, the role of parental or peer influence in the behaviors or characteristics of an individual.

Subfields

Psychology encompasses a vast domain, and includes many different approaches to the study of mental processes and behavior. Below are the major areas of inquiry that comprise psychology. A comprehensive list of the sub-fields and areas within psychology can be found at the list of psychology topics and list of psychology disciplines.

Abnormal

Abnormal psychology is the study of abnormal behavior in order to describe, predict, explain, and change abnormal patterns of functioning. Abnormal psychology studies the nature of psychopathology and its causes, and this knowledge is applied in clinical psychology to treat patients with psychological disorders.

It can be difficult to draw the line between normal and abnormal behaviors. In general, abnormal behaviors must be maladaptive and cause an individual significant discomfort in order to be of clinical and research interest. According to the DSM-IV-TR, behaviors may be considered abnormal if they are associated with disability, personal distress, the violation of social norms, or dysfunction.

Biological

Biological psychology is the scientific study of the biological substrates of behavior and mental states. Seeing all behavior as intertwined with the nervous system, biological psychologists feel it is sensible to study how the brain functions in order to understand behavior. This is the approach taken in behavioral neuroscience, cognitive neuroscience, and neuropsychology. Neuropsychology is the branch of psychology that aims to understand how the structure and function of the brain relate to specific behavioral and psychological processes. Neuropsychology is particularly concerned with the understanding of brain injury in an attempt to work out normal psychological function. The approach of cognitive neuroscience to studying the link between brain and behavior is to use neuroimaging tools, such as to observe which areas of the brain are active during a particular task.

Cognitive

Cognitive psychology studies cognition, the mental processes underlying behavior. Perception, learning, problem solving, memory, attention, language and emotion are all well-researched areas. Cognitive psychology is associated with a school of thought known as cognitivism, whose adherents argue for an information processing model of mental function, informed by positivism and experimental psychology.

On a broader level, cognitive science is a conjoined enterprise of cognitive psychologists, neurobiologists, researchers in artificial intelligence, logicians, linguists, and social scientists, and places a slightly greater emphasis on computational theory and formalization. Both areas can use computational models to simulate phenomena of interest. Because mental events cannot directly be observed, computational models provide a tool for studying the functional organization of the mind. Such models give cognitive psychologists a way to study the ''software'' of mental processes independent of the ''hardware'' it runs on, be it the brain or a computer.

Comparative

Comparative psychology refers to the study of the behavior and mental life of animals other than human beings. It is related to disciplines outside of psychology that study animal behavior such as ethology. Although the field of psychology is primarily concerned with humans the behavior and mental processes of animals is also an important part of psychological research. This being either as a subject in its own right (e.g., animal cognition and ethology) or with strong emphasis about evolutionary links, and somewhat more controversially, as a way of gaining an insight into human psychology. This is achieved by means of comparison or via animal models of emotional and behavior systems as seen in neuroscience of psychology (e.g., affective neuroscience and social neuroscience).

Counseling

Counseling psychology seeks to facilitate personal and interpersonal functioning across the lifespan with a focus on emotional, social, vocational, educational, health-related, developmental, and organizational concerns. Counselors are primarily clinicians, using psychotherapy and other interventions in order to treat clients. Traditionally, counseling psychology has focused more on normal developmental issues and everyday stress rather than psychopathology, but this distinction has softened over time. Counseling psychologists are employed in a variety of settings, including universities, hospitals, schools, governmental organizations, businesses, private practice, and community mental health centers.

Clinical

Clinical psychology includes the study and application of psychology for the purpose of understanding, preventing, and relieving psychologically-based distress or dysfunction and to promote subjective well-being and personal development. Central to its practice are psychological assessment and psychotherapy, although clinical psychologists may also engage in research, teaching, consultation, forensic testimony, and program development and administration.

Some clinical psychologists may focus on the clinical management of patients with brain injury—this area is known as clinical neuropsychology. In many countries clinical psychology is a regulated mental health profession.

The work performed by clinical psychologists tends to be influenced by various therapeutic approaches, all of which involve a formal relationship between professional and client (usually an individual, couple, family, or small group). The various therapeutic approaches and practices are associated with different theoretical perspectives and employ different procedures intended to form a therapeutic alliance, explore the nature of psychological problems, and encourage new ways of thinking, feeling, or behaving. The four major theoretical perspectives are Psychodynamic, Cognitive Behavioral, Existential-Humanistic, and Systems or Family therapy. There has been a growing movement to integrate the various therapeutic approaches, especially with an increased understanding of issues regarding culture, gender, spirituality, and sexual-orientation. With the advent of more robust research findings regarding psychotherapy, there is growing evidence that most of the major therapies are about of equal effectiveness, with the key common element being a strong therapeutic alliance. Because of this, more training programs and psychologists are now adopting an eclectic therapeutic orientation.

Critical

Critical psychology applies the methodology of critical theory to psychology. As such, it critiques not only the psychic substrates of the ''status quo'', but also the elements of mainstream psychology that are, themselves, seen as contributors to oppressive ideologies. Critical psychology operates on the belief ''that mainstream psychology has institutionalized a narrow view of the field’s ethical mandate to promote human welfare'' by promoting individual remedies to social ills, encouraging trivial and inconsequential research, and engaging in other practices that its positivistic methods fail to place under critical scrutiny.

A critical psychologist might ask whether a case of ''work stress'' warrants efforts to change the macro-level systems that control the work, rather than merely to treat the individual who experiences the stress—or, more accurately, who shares the stress with countless other individuals. One might also ask why ''mainstream trauma efforts fail to incorporate a focus on human rights and social justice'' in war-ravaged communities. In short, critical psychology seeks, where it deems appropriate, to raise psychology's level of analysis from the individual to society, and to render psychology more transformative than ameliorative. Critical psychology has been applied to a wide array of psychology's other subfields, and many of its theorists are employed in mainstream psychological professions.

Developmental

Mainly focusing on the development of the human mind through the life span, developmental psychology seeks to understand how people come to perceive, understand, and act within the world and how these processes change as they age. This may focus on intellectual, cognitive, neural, social, or moral development. Researchers who study children use a number of unique research methods to make observations in natural settings or to engage them in experimental tasks. Such tasks often resemble specially designed games and activities that are both enjoyable for the child and scientifically useful, and researchers have even devised clever methods to study the mental processes of small infants. In addition to studying children, developmental psychologists also study aging and processes throughout the life span, especially at other times of rapid change (such as adolescence and old age). Developmental psychologists draw on the full range of theorists in scientific psychology to inform their research.

Educational

Educational psychology is the study of how humans learn in educational settings, the effectiveness of educational interventions, the psychology of teaching, and the social psychology of schools as organizations. The work of child psychologists such as Lev Vygotsky, Jean Piaget and Jerome Bruner has been influential in creating teaching methods and educational practices. Educational psychology is often included in teacher education programs, at least in North America, Australia, and New Zealand.

Evolutionary

Evolutionary psychology explores the genetic roots of mental and behavioral patterns, and posits that common patterns may have emerged because they were highly adaptive for humans in the environments of their evolutionary past—even if some of these patterns are maladaptive in today's environments. Fields closely related to evolutionary psychology are animal behavioral ecology, human behavioral ecology, dual inheritance theory, and sociobiology. Memetics, founded by British evolutionary biologist Richard Dawkins, is a related but competing field that proposes that cultural evolution can occur in a Darwinian sense but independently of Mendelian mechanisms; it therefore examines the ways in which thoughts, or memes, may evolve independently of genes.

Forensic

Forensic psychology covers a broad range of practices including the clinical evaluations of defendants, reports to judges and attorneys, and courtroom testimony on given issues. Forensic psychologists are appointed by the court or hired by attorneys to conduct competency to stand trial evaluations, competency to be executed evaluations, sanity evaluations, involuntary commitment evaluations, provide sentencing recommendations, and sex offender evaluation and treatment evaluations and provide recommendations to the court through written reports and testimony. Many of the questions the court asks the forensic psychologist go ultimately to legal issues, although a psychologist cannot answer legal questions. For example, there is no definition of sanity in psychology. Rather, sanity is a legal definition that varies from place to place throughout the world. Therefore, a prime qualification of a forensic psychologist is an intimate understanding of the law, especially criminal law.

Global

Global psychology is a subfield of psychology that addresses the issues raised in the global sustainability debate. Like critical psychology, global psychology expands the objective of psychology to macro-level trends; it examines the overwhelming consequences of global warming, economic destabilization and other large-scale phenomena, while recognizing that global sustainability can best be achieved by psychologically sound individuals and cultures. Global psychologists advocate a simple and sensible, yet comprehensive, psychology, whose strength is its focus on the long-term well-being of all of humanity.

Health

Health psychology is the application of psychological theory and research to health, illness and health care. Whereas clinical psychology focuses on mental health and neurological illness, health psychology is concerned with the psychology of a much wider range of health-related behavior including healthy eating, the doctor-patient relationship, a patient's understanding of health information, and beliefs about illness. Health psychologists may be involved in public health campaigns, examining the impact of illness or health policy on quality of life and in research into the psychological impact of health and social care.

Industrial/organizational

Industrial and organizational psychology (I/O) applies psychological concepts and methods to optimize human potential in the workplace. Personnel psychology, a subfield of I/O psychology, applies the methods and principles of psychology in selecting and evaluating workers. I/O psychology's other subfield, organizational psychology, examines the effects of work environments and management styles on worker motivation, job satisfaction, and productivity.

Legal

Legal psychology is a research-oriented field populated with researchers from several different areas within psychology (although social and cognitive psychologists are typical). Legal psychologists explore such topics as jury decision-making, eyewitness memory, scientific evidence, and legal policy. The term ''legal psychology'' has only recently come into use, and typically refers to any non-clinical law-related research.

Occupational health

Occupational health psychology (OHP) is a discipline that emerged out of health psychology, industrial/organizational psychology, and occupational health. OHP is concerned with identifying psychosocial characteristics of workplaces that give rise to problems in physical (e.g., cardiovascular disease) and mental health (e.g., depression). OHP has investigated such psychosocial characteristics of workplaces as workers' decision latitude and supervisors' supportiveness. OHP also concerns itself with interventions that can prevent or ameliorate work-related health problems. Such interventions have important, beneficial implications for the economic success of organizations. Other research areas of concern to OHP include workplace violence, unemployment, and workplace safety. Two exemplary OHP journals are the ''Journal of Occupational Health Psychology'' and ''Work & Stress''. Two prominent OHP professional organizations include the European Academy of Occupational Health Psychology and the Society for Occupational Health Psychology.

Personality

Personality psychology studies enduring patterns of behavior, thought, and emotion in individuals, commonly referred to as personality. Theories of personality vary across different psychological schools and orientations. They carry different assumptions about such issues as the role of the unconscious and the importance of childhood experience. According to Freud, personality is based on the dynamic interactions of the ego, superego, and id. Trait theorists, in contrast, attempt to analyze personality in terms of a discrete number of key traits by the statistical method of factor analysis. The number of proposed traits has varied widely. An early model proposed by Hans Eysenck suggested that there are three traits that comprise human personality: extraversion-introversion, neuroticism, and psychoticism. Raymond Cattell proposed a theory of 16 personality factors. The ''Big Five'' or Five Factor Model, proposed by Lewis Goldberg currently has strong support among trait theorists.

Quantitative

Quantitative psychology involves the application of mathematical and statistical modeling in psychological research, and the development of statistical methods for analyzing and explaining behavioral data. The term ''Quantitative psychology'' is relatively new and little used (only recently have Ph.D. programs in quantitative psychology been formed), and it loosely covers the longer standing subfields psychometrics and mathematical psychology.

Psychometrics is the field of psychology concerned with the theory and technique of psychological measurement, which includes the measurement of knowledge, abilities, attitudes, and personality traits. Measurement of these phenomena is difficult, and much research has been developed to define and analyze such phenomena. Psychometric research typically involves two major research tasks, namely: (i) the construction of instruments and procedures for measurement; and (ii) the development and refinement of theoretical approaches to measurement.

Mathematical psychology is the subdiscipline that is concerned with the development of psychological theory in relation with mathematics and statistics. Basic topics in mathematical psychology include measurement theory and mathematical learning theory as well as the modeling and analysis of mental and motor processes. Psychometrics is more associated with educational psychology, personality, and clinical psychology. Mathematical psychology is more closely related to psychonomics/experimental and cognitive, and physiological psychology and (cognitive) neuroscience.

Social

Social psychology is the study of social behavior and mental processes, with an emphasis on how humans think about each other and how they relate to each other. Social psychologists are especially interested in how people react to social situations. They study such topics as the influence of others on an individual's behavior (e.g. conformity, persuasion), and the formation of beliefs, attitudes, and stereotypes about other people. Social cognition fuses elements of social and cognitive psychology in order to understand how people process, remember, and distort social information. The study of group dynamics reveals information about the nature and potential optimization of leadership, communication, and other phenomena that emerge at least at the microsocial level. In recent years, many social psychologists have become increasingly interested in implicit measures, mediational models, and the interaction of both person and social variables in accounting for behavior.

School

School psychology combines principles from educational psychology and clinical psychology to understand and treat students with learning disabilities; to foster the intellectual growth of ''gifted'' students; to facilitate prosocial behaviors in adolescents; and otherwise to promote safe, supportive, and effective learning environments. School psychologists are trained in educational and behavioral assessment, intervention, prevention, and consultation, and many have extensive training in research. Currently, school psychology is the only field in which a professional can be called a ''psychologist'' without a doctoral degree, with the National Association of School Psychologists (NASP) recognizing the Specialist degree as the entry level. This is a matter of controversy as the APA does not recognize anything below a doctorate as the entry level for a psychologist. Specialist-level school psychologists, who typically receive three years of graduate training, function almost exclusively within school systems, while those at the doctoral-level are found in a number of other settings as well, including universities, hospitals, clinics, and private practice.

Research methods

Research in most areas of psychology is conducted in broad accord with the standards of the scientific method, encompassing both qualitative ethological and quantitative statistical modalities to generate and evaluate explanatory hypotheses with regard to psychological phenomena. Investigation may be pursued by experimental protocols, but alternative methods are sometimes preferred due to research ethics, the state of development in a given research domain, and other reasons.

Psychology tends to be eclectic, drawing on knowledge from other fields to help explain and understand psychological phenomena. For example, evolutionary psychologists may synthesize data from multiple subfields of psychology, biology, and anthropology. Additionally, psychologists make extensive use of the three modes of inference that were identified by C. S. Peirce: Deduction, induction, and abduction (hypothesis generation). While often employing deductive-nomological reasoning, they also rely on inductive reasoning to generate explanations. For example, evolutionary psychologists propose explanations of human behavior in terms of such behaviors' advantages for hunter-gatherers.

Qualitative psychological research uses many observational methods, including action research, ethnography, exploratory statistics, structured interviews, and participant observation, to enable the gathering of rich information that is difficult to obtain by experimentation. The tentative conclusions of such exploratory studies can be assessed by statistical hypothesis testing, for example by asking a new sample of subjects to evaluate the conclusions of the previous qualitative study. Research in humanistic psychology is often pursued via ethnographic, historical, and historiographic methods. Psychodynamic research has traditionally entailed interpreting clinical case studies, and subschools ranging from Freudian psychoanalysis to Neo-Jungian archetypal psychology have employed myth as a vehicle of interpretation. Recent developments, particularly in neuro-psychoanalysis, have demanded a closer adherence to scientific standards.

A precursor to critical psychology, liberation psychology, cited traditional surveys in its emancipatory quests. In general, though, their methods tend to be critical rather than positivistic, and therefore tend not only to avoid the scientific method, but also to identify the ways in which this method is improperly used and downright abused. Taking a reflexive approach, critical psychologists both scrutinize the current state of psychological affairs, and seek defensible positions on the ''old questions—such as free will vs. determinism, nature vs. nurture, [and] consciousness vs. unconscious forces''.

The testing of different aspects of psychological function is a significant area of mainstream psychology. Psychometric and statistical methods predominate, including various well-known standardized tests as well as those created ad hoc as the situation or experiment requires.

Academic psychologists may focus purely on research and psychological theory, aiming to further psychological understanding in a particular area, while other psychologists may work in applied psychology to deploy such knowledge for immediate and practical benefit. These approaches are not mutually exclusive, and many psychologists will be involved in both researching and applying psychology at some point during their career. Many clinical psychology programs aim to develop in practicing psychologists both knowledge of and experience with research and experimental methods, which they may interpret and employ as they treat individuals with psychological issues.

When an area of interest requires specific training and specialist knowledge, especially in applied areas, psychological associations normally establish a governing body to manage training requirements. Similarly, requirements may be laid down for university degrees in psychology, so that students acquire an adequate knowledge in a number of areas. Additionally, areas of practical psychology, where psychologists offer treatment to others, may require that psychologists be licensed by government regulatory bodies as well.

Controlled experiments

Experimental psychological research is conducted in a laboratory under controlled conditions. This method of research relies on the application of the scientific method to understand behavior. Experimenters use several types of measurements, including rate of response, reaction time, and various psychometric measurements. Experiments are designed to test specific hypotheses (deductive approach) or evaluate functional relationships (inductive approach). They allow researchers to establish causal relationships between different aspects of behavior and the environment. In an experiment, one or more variables of interest are controlled by the experimenter (independent variable) and another variable is measured in response to different conditions (dependent variable). Experiments are one of the primary research methods in many areas of psychology, particularly cognitive/psychonomics, mathematical psychology, psychophysiology and biological psychology/cognitive neuroscience.

Experiments on humans have been put under some controls, namely informed and voluntary consent. After World War II, the Nuremberg Code was established, because of Nazi abuses of experimental subjects. Later, most countries (and scientific journals) adopted the Declaration of Helsinki. In the US, the National Institutes of Health established the Institutional Review Board in 1966, and in 1974 adopted the National Research Act (HR 7724). All of these measures encouraged researchers to obtain informed consent from human participants in experimental studies. A number of influential studies led to the establishment of this rule; such studies included the MIT and Fernald School radioisotope studies, the Thalidomide tragedy, the Willowbrook hepatitis study, and Stanley Milgram's studies of obedience to authority.

Survey questionnaires

Statistical surveys are used in psychology for measuring attitudes and traits, monitoring changes in mood, checking the validity of experimental manipulations, and for a wide variety of other psychological topics. Most commonly, psychologists use paper-and-pencil surveys. However, surveys are also conducted over the phone or through e-mail. Increasingly, web-based surveys are being used in research. Similar methodology is also used in applied setting, such as clinical assessment and personnel assessment.

Longitudinal studies

A longitudinal study is a research method which observes a particular population over time. For example, one might wish to study specific language impairment (SLI) by observing a group of individuals with the condition over a period of time. This method has the advantage of seeing how a condition can affect individuals over long time scales. However, such studies can suffer from attrition due to drop-out or death of subjects. In addition, since individual differences between members of the group are not controlled, it may be difficult to draw conclusions about the populations.

Longitudinal study is a developmental research strategy that involves testing an age group repeatedly over many years. Longitudinal studies answer vital questions about how people develop. This developmental research follows people over years and the outcome has been an incredible array of findings, especially relating to psychological problems.

Some longitudinal studies are experiments, called repeated-measures experiments. Psychologists often use the crossover design to reduce the influence of confounding covariates and to reduce the number of subjects.

Observation in natural settings

In the same way Jane Goodall studied the role of chimpanzee social and family life, psychologists conduct similar observational studies in human social, professional and family lives. Sometimes the participants are aware they are being observed and other times it is covert: the participants do not know they are being observed. Ethical guidelines need to be taken into consideration when covert observation is being carried out.

Qualitative and descriptive research

Research designed to answer questions about the current state of affairs such as the thoughts, feelings and behaviors of individuals is known as descriptive research. Descriptive research can be qualitative or quantitative in orientation. Qualitative research is descriptive research that is focused on observing and describing events as they occur, with the goal of capturing all of the richness of everyday behavior and with the hope of discovering and understanding phenomena that might have been missed if only more cursory examinations have been made.

Neuropsychological methods

Neuropsychology involves the study of both healthy individuals and patients, typically who have suffered either brain injury or mental illness.

Cognitive neuropsychology and cognitive neuropsychiatry study neurological or mental impairment in an attempt to infer theories of normal mind and brain function. This typically involves looking for differences in patterns of remaining ability (known as 'functional disassociations') which can give clues as to whether abilities are comprised of smaller functions, or are controlled by a single cognitive mechanism.

In addition, experimental techniques are often used to study the neuropsychology of healthy individuals. These include behavioral experiments, brain-scanning or functional neuroimaging, used to examine the activity of the brain during task performance, and techniques such as transcranial magnetic stimulation, which can safely alter the function of small brain areas to reveal their importance in mental operations.

Computational modeling

Computational modeling is a tool often used in mathematical psychology and cognitive psychology to simulate a particular behavior using a computer. This method has several advantages. Since modern computers process extremely quickly, many simulations can be run in a short time, allowing for a great deal of statistical power. Modeling also allows psychologists to visualize hypotheses about the functional organization of mental events that couldn't be directly observed in a human.

Several different types of modeling are used to study behavior. Connectionism uses neural networks to simulate the brain. Another method is symbolic modeling, which represents many different mental objects using variables and rules. Other types of modeling include dynamic systems and stochastic modeling.

Animal studies

Animal learning experiments are important in many aspects of psychology such as investigating the biological basis of learning, memory and behavior. In the 1890s, physiologist Ivan Pavlov famously used dogs to demonstrate classical conditioning. Non-human primates, cats, dogs, rats and other rodents are often used in psychological experiments. Controlled experiments involve introducing only one variable at a time, which is why animals used for experiments are housed in laboratory settings. In contrast, human environments and genetic backgrounds vary widely, which makes it difficult to control important variables for human subjects.