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Psychology is an academic and applied discipline involving the phenomenological and scientific study of mental processes and behaviour. Psychologists study such concepts as perception, cognition, emotion, personality, behaviour, interpersonal relationships, and the individual and collective unconscious. Psychology also refers to the application of such knowledge to various spheres of human activity including issues related to daily life—e.g. family, education, and work—and the treatment of mental health problems. Psychology attempts to understand the role these functions play in social behaviour and in social dynamics, while incorporating the underlying physiological and neurological processes into its conceptions of mental functioning. Psychology includes many sub-fields of study and application concerned with such areas as human development, sports, health, industry, media, law.
Philosophical and scientific roots
The study of psychology in a philosophical context dates back to the ancient civilizations of Egypt, Greece, China and India. Psychology began adopting a more clinical and experimental approach under medieval Muslim psychologists and physicians, who built psychiatric hospitals for such purposes.
Though the use of psychological experimentation dates back to Alhazen's Book of Optics in 1021, 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". 1879 is thus sometimes regarded as the "birthdate" of psychology. The American philosopher William James published his seminal book, Principles of Psychology, in 1890, while laying the foundations for many of the questions that psychologists would focus on 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.
During the 1890s, 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. Freud also had a significant influence on Carl Jung, whose analytical psychology became an alternative form of depth psychology. Philosopher Karl Popper argued that Freud's psychoanalytic theories were presented in untestable form. Due to their subjective nature, Freud's theories are often of limited interest to many scientifically-oriented psychology departments. Followers of Freud who accept the basic ideas of psychoanalysis but alter it in some way are called neo-Freudians. Modification of Jung's theories has led to the archetypal and process-oriented schools of psychological thought.
Partly in opposition to the subjective and introspective nature of Freudian psychodynamics, and its focus on the recollection of childhood experiences, during the early decades of the 20th century, behaviorism gained popularity as a guiding psychological theory. Founded by John B. Watson and embraced and extended by Edward Thorndike, Clark L. Hull, Edward C. Tolman, and later B.F. Skinner, behaviorism was grounded in animal experimentation in the laboratory. Behaviorists shared the view that the subject matter of psychology should be operationalized with standardized procedures which led psychology to focus on behaviour, not the mind or consciousness. They doubted the validity of introspection for studying internal mental states such as feelings, sensations, beliefs, desires, and other unobservable entities. In "Psychology as the Behaviorist Views It" (1913), Watson argued that psychology "is a purely objective experimental branch of natural science," that "introspection forms no essential part of its methods," and that "the behaviorist recognizes no dividing line between man and brute." Skinner rejected hypothesis testing as a research method, considering it to be too conducive to speculative theories that would promote useless research and stifle good research.
Behaviorism was the dominant paradigm in American psychology throughout the first half of the 20th century. However, the modern field of psychology is largely dominated by cognitive psychology. Linguist Noam Chomsky helped spark the cognitive revolution in psychology through his review of B. F. Skinner's Verbal Behavior, in which he challenged the behaviorist approach to the study of behavior and language dominant in the 1950s. Chomsky was highly critical of what he considered arbitrary notions of 'stimulus', 'response' and 'reinforcement' which Skinner borrowed from animal experiments in the laboratory. Chomsky argued that Skinner's notions could only be applied to complex human behaviour, such as language acquisition, in a vague and superficial manner. Chomsky emphasized that research and analysis must not ignore the contribution of the child in the acquisition of language and proposed that humans are born with an natural ability to acquire language. Work most associated with psychologist Albert Bandura, who initiated and studied social learning theory, showed that children could learn aggression from a role model through observational learning, without any change in overt behaviour, and so must be accounted for by internal processes.
Existentialism and humanism
Humanistic psychology was developed in the 1950s in reaction to both behaviorism and psychoanalysis, arising largely from the existential philosophy of writers such as Jean-Paul Sartre and Søren Kierkegaard. By using phenomenology, intersubjectivity and first-person categories, the humanistic approach seeks to glimpse the whole person--not just the fragmented parts of the personality or cognitive functioning. Humanism focuses on uniquely human issues and fundamental issues of life, such as self-identity, death, aloneness, freedom, and meaning. Some of the founding theorists behind this school of thought were Abraham Maslow who formulated a hierarchy of human needs, Carl Rogers who created and developed Client-centered therapy, and Fritz Perls who helped create and develop Gestalt therapy. It became so influential as to be called the "third force" within psychology (along with behaviorism and psychoanalysis).
As computer technology proliferated, so emerged the metaphor of mental function as information processing. This, combined with a scientific approach to studying the mind, as well as a belief in internal mental states, led to the rise of cognitivism as a popular model of the mind. Cognitive psychology differs from other psychological perspectives in two key ways. First, it accepts the use of the scientific method, and generally rejects introspection as a method of investigation, unlike symbol-driven approaches such as Freudian psychodynamics. Second, it explicitly acknowledges the existence of internal mental states (such as belief, desire and motivation), whereas behaviorism does not.
Links between brain and nervous system function also became understood, partly due to the experimental work of people such as Charles Sherrington and Donald Hebb, and partly due to studies of people with brain injury (see cognitive neuropsychology). With the development of technologies for measuring brain function, neuropsychology and cognitive neuroscience have become increasingly active areas of contemporary psychology. Cognitive psychology has been subsumed along with other disciplines, such as philosophy of mind, computer science, and neuroscience, under the umbrella discipline of cognitive science.
Mind and brain
Psychology describes and attempts to explain consciousness, behavior, and social interaction. Empirical psychology is primarily devoted to describing human experience and behaviour as it actually occurs. Since the 1980s, psychology has begun to examine the relationship between consciousness and the brain or nervous system. It is still not clear how these interact: does consciousness determine brain states or do brain states determine consciousness--or are both going on in various ways? Or, is consciousness some sort of complicated 'illusion' that bears no direct relationship to neural processes? Perhaps to understand this, it is necessary to define " consciousness" and "brain state". An understanding of brain function is increasingly being included in psychological theory and practice, particularly in areas such as artificial intelligence, neuropsychology, and cognitive neuroscience.
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 behaviour 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).
Psychology encompasses a vast domain, and includes many different approaches to the study of mental processes and behaviour. Below are the major areas of inquiry that comprise psychology, divided into fields of research psychology and fields of applied psychology. A comprehensive list of the sub-fields and areas within psychology can be found at the list of psychological topics and list of psychology disciplines.
Abnormal psychology is the study of abnormal behaviour 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 a patient with psychological disorders.
In the study of abnormal behaviour, it can be difficult to define the line between which behaviors are considered normal and which are not. In general, abnormal behaviors must be maladaptive and cause an individual subjective discomfort (signs of emotional distress). Generally, abnormal behaviors are classified as:
- Abnormal as in "infrequent" in relation to the overall population.
- Abnormal as in "maladaptive". The behaviour fails to promote well being, growth, and fulfillment of a person.
- Abnormal as in "deviant". The behaviour is not socially acceptable.
- Abnormal as in "unjustifiable". The behaviour that cannot be rationalized.
Biological psychology is the scientific study of the biological bases of behavior and mental states. Because all behaviour is controlled by the central nervous system, it is sensible to study how the brain functions in order to understand behaviour. This is the approach taken in behavioural 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 behavioural and psychological processes. Often neuropsychologists are employed as scientists to advance scientific or medical knowledge. 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 behaviour is to use neuroimaging tools, such as to observe which areas of the brain are active during a particular task.
The nature of thought is another core interest in psychology. Cognitive psychology studies cognition, the mental processes underlying behaviour. It uses information processing as a framework for understanding the mind. 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.
Cognitive science is a conjoined enterprise of cognitive psychologists, neurobiologists, workers 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 psychology refers to the study of the behaviour and mental life of animals other than human beings. It is related to disciplines outside of psychology that study animal behaviour, such as ethology. Although the field of psychology is primarily concerned with humans, the behaviour and mental processes of animals is also an important part of psychological research, 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 by means of comparison or via animal models of emotional and behaviour systems as seen in neuroscience of psychology (e.g., affective neuroscience and social neuroscience).
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). Urie Bronfenbrenner's theory of development in context (The Ecology of Human Development - ISBN 0-674-22456-6) is influential in this field, as are those mentioned in "Educational psychology" immediately below, as well as many others. Developmental psychologists draw on the full range of theorists in scientific psychology to inform their research.
Personality psychology studies enduring psychological patterns of behaviour, thought and emotion, commonly called an individual's personality. Theories of personality vary between different psychological schools. Trait theories attempts to break personality down into a number of traits, by use of factor analysis. The number of traits have varied between theories. One of the first, and smallest, models was that of Hans Eysenck, which had three dimensions: extroversion— introversion, neuroticism—emotional stability, and psychoticism. Raymond Cattell proposed a theory of 16 personality factors. The theory that has most empirical evidence behind it today may be the " Big Five" theory, proposed by Lewis Goldberg, and others.
A different, but well known approach to personality is that of Sigmund Freud, whose structural theory of personality divided personality into the ego, superego, and id. He utilized the principles of thermodynamics metaphorically to explain these three distinctive and interacting tripartite divisions. In 1923 Freud published the ground-breaking book: "The Ego and the Id" in which he named and identified the functioning psychodynamics of human personality. This theory has been used in modern psychology paradigms such as Transactional Analysis. However, Freud's theory of personality has been criticized by many, including many mainstream psychologists.
Quantitative psychology involves the application of mathematical and statistical modeling in psychological research, and the development of statistical methods for analyzing and explaining behavioural 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 unobservable phenomena is difficult, and much of the research and accumulated knowledge in this discipline has been developed in an attempt to properly define and quantify 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.
Whereas psychometrics is mainly concerned with individual differences and population structure, mathematical psychology is concerned with modeling of mental and motor processes of the average individual. 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.
Basic research encompasses the study of behaviour for use in academic settings, and contains numerous areas: abnormal psychology, biological psychology, cognitive psychology, comparative psychology, developmental psychology, health psychology, personality psychology, social psychology and others. Quantitative psychology is contrasted with applied psychology.
Social psychology is the study of the nature and causes of human social behavior and mental processes, with an emphasis on how people think towards each other and how they relate to each other. Social Psychology aims to understand how we make sense of social situations. For example, social psychologists study the influence of others on an individual's behaviour (e.g., conformity or persuasion), the perception and understanding of social cues, or the formation of attitudes or stereotypes about other people. Social cognition is a common approach and involves a mostly cognitive and scientific approach to understanding social behaviour.
Fields of applied research
Applied psychology encompasses both psychological research that is designed to help individuals overcome practical problems and the application of this research in applied settings. Much of applied psychology research is utilized in other fields, such as business management, product design, ergonomics, nutrition, law and clinical medicine. Applied psychology includes the areas of clinical psychology, industrial and organizational psychology, human factors, psychology and law, health psychology, school psychology, community psychology and others.
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 done inside various therapy models, all of which involve a formal relationship between professional and client—usually an individual, couple, family, or small group—that employs a set of 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 perspectives are Psychodynamic, Cognitive Behavioural, Existential-Humanistic, and Systems or Family therapy. There has been a growing movement to integrate these 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.
Clinical psychologists do not usually prescribe medication, although there is a growing movement for psychologists to have limited prescribing privileges. In general, however, when medication is warranted many psychologists will work in cooperation with psychiatrists so that clients get all their therapeutic needs met. Clinical psychologists may also work as part of a team with other professionals, such as social workers and nutritionists.
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.
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.
Forensic psychology covers a broad range of practices primarily involving evaluations of defendants, reports to judges and attorneys, and courtroom testimony on given issues. Forensic psychologists are appointed by the court 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. Most of the questions the court asks the forensic psychologist are not questions of psychology but rather legal questions. For example, there is no definition of sanity in psychology. Rather, sanity is a legal definition that varies from state to state in the United States and from jurisdiction to jurisdiction. Therefore, a prime qualification of a forensic psychologist is an intimate understanding of the law, especially criminal law.
Psychology and Law
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.
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 behaviour 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.
Human factors psychology
Human factors psychology (sometimes called Engineering Psychology) is the study of how cognitive and psychological processes affect our interaction with tools and objects in the environment. The goal of research in human factors psychology is to better design objects by taking into account the limitations and biases of human mental processes and behaviour.
Industrial and organizational psychology
Industrial and organizational psychology (I/O) is among the newest fields in psychology. Industrial Psychology focuses on improving, evaluating, and predicting job performance while Organizational Psychology focuses on how organizations impact and interact with individuals as well as how the individuals affect the organisational culture. In 1910, through the works and experiments of Hugo Munsterberg and Walter Dill Scott, Industrial Psychology became recognized as a legitimate part of the social science. Organizational Psychology was not officially added until the 1970s and since then, the field has flourished. The Society for Industrial Organizational Psychology has approximately 3400 professional members and 1900 student members. These two numbers combine to make up only about four percent of the members in the American Psychological Association but the number has been rising since 1939 when there were only one hundred professional I/O psychologists.
I/O psychologists are employed by academic institutions, consulting firms, internal human resources in industries, and governmental institutions. Various universities across the United States are beginning to strengthen their I/O Psychology programs due to the increase of interest and job demand in the field.
Industrial organizational psychologists look at questions regarding things such as who to hire, how to define and measure successful job performance, how to prepare people to be more successful in their jobs, how to create and change jobs so that they are safer and make people happier, and how to structure the organization to allow people to achieve their potential.
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 behaviours in adolescents; and otherwise to promote safe, supportive, and effective learning environments. School psychologists are trained in educational and behavioural 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 in experimental 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. Where research ethics and the state of development in a given research domain permits, investigation may be pursued by experimental protocols. Psychology tends to be eclectic, drawing on knowledge from other fields to help explain and understand psychological phenomena. Qualitative psychological research utilizes a broad spectrum of observational methods, including action research, ethography, exploratory statistics, structured interviews, and participant observation, to enable the gathering of rich information unattainable by classical experimentation. Research in humanistic psychology is more typically pursued via ethnographic, historical, and historiographic methods.
The testing of different aspects of psychological function is a significant area of contemporary 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.
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 behaviour. 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 are important for psychological research because they allow researchers to establish causal relationships between different aspects of behaviour and the environment. Importantly, 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). (See also hypothesis testing.) Experiments are one of the primary research methodologies in many areas of psychology, particularly cognitive/ psychonomics, mathematical psychology, psychophysiology and biological psychology/ cognitive neuroscience.
As an example, suppose an experimenter wanted to answer the following question: does talking on a phone affect one's ability to stop quickly while driving? To answer this, the experimenter would want to show that a subject's stopping time is different when they are talking on a phone versus when they are not. If the experiment is properly conducted in a controlled environment and a difference between the two conditions is found, the experimenter would be able to show a causal relationship between phone use and stopping time. In addition to potential practical benefits, this type of experiment may have important theoretical results, such as helping to explain the processes that underlie attention in humans.
Experiments on humans have been put under some controls; namely informed and voluntary consent. After WWII, 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 NIH established the IRB in 1966. And in 1974, adopted the National Research Act (HR 7724). All of which cover informed consent of human participants in experimental studies. There were a number of influential studies which lead to the establishment of these rules, including the MIT & Fernald School radioisotope studies, the Thalidomide Tragedy, Willowbrook hepatitis study, Milgram's obedience to authority studies.
Animal learning experiments are important in many aspects of psychology such as investigating the biological basis of learning, memory and behaviour. 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.
Qualitative and descriptive research
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.
Statistical surveys are used in psychology for measuring attitudes and traits, monitoring changes in mood, or checking the validity of experimental manipulations. 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.
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.
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 disassociation's') 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 which also apply to studying the neuropsychology of healthy individuals. These include behavioural 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 investigate their importance in mental operations.
Computational modeling is a tool often used in mathematical psychology and cognitive psychology to simulate a particular behaviour 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 behaviour. 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.
Criticism and controversies
Status as a science
A common criticism of psychology concerns its fuzziness as a science. Philosopher Thomas Kuhn's 1962 critique implied psychology overall was in a pre-paradigm state, lacking the agreement on overarching theory found in mature sciences such as chemistry and physics. Because some areas of psychology rely on research methods such as surveys and questionnaires, critics have claimed that psychology is not as scientific as many assume. Methods such as introspection and psychoanalysis, used by some psychologists, are inherently subjective.
The validity of probability testing as a research tool has been called into question. There is concern that this statistical method may promote trivial findings as meaningful, especially when large samples are used. Some psychologists have responded with an increased use of effect size statistics, rather than sole reliance on the traditional p<.05 decision rule in statistical hypothesis testing.
In recent years, and particularly in the U.S., there has been increasing debate about the nature of therapeutic effectiveness and about the relevance of empirically examining psychotherapeutic strategies. One argument states that some therapies are based on discredited theories and are unsupported by empirical evidence. The other side points to recent research suggesting that all mainstream therapies are of about equal effectiveness, while also arguing that controlled studies often do not take into consideration real-world conditions (e.g. the high co-morbidity rate or the experience of clinicians); that research is heavily biased towards the methods of the cognitive behavioural therapies (CBT); and that it typically under-represents minority groups.
Concern about fringe clinical practices
There is also concern from researchers about a perceived gap between scientific theory and its application, in particular with the application of esoteric practices. Exponents of evidence-based approaches to clinical psychology practice say that the gap is increasing, and researchers such as Beyerstein (2001) say there has been a large increase in the number of mental health training programs that do not emphasize science training. According to Lilienfeld (2002) “a wide variety of unvalidated and sometimes harmful psychotherapeutic methods, including psychoanalysis, facilitated communication for infantile autism, suggestive techniques for memory recovery (e.g., hypnotic age-regression, guided imagery, body work), energy therapies (e.g., Thought Field Therapy, Emotional Freedom Technique), and New Age therapies of seemingly endless stripes (e.g., rebirthing, reparenting, past-life regression, Primal Scream therapy, neurolinguistic programming ) have either emerged or maintained their popularity in recent decades." Allen Neuringer made a similar point in the field of the experimental analysis of behaviour in 1984. There are some differences of opinion over the actual extent of the research practitioner gap, but the consensus is on the concern about fringe or quack practices, and the legal view favours the use of empirical validation for any psychological intervention (Faigman and Monahan 2005). The emphasis on improvement of evidence based practice has been made in order to increase the general public's confidence in the health professions, and to avoid instances whereby clients forgo evidence based treatments in favour of unvalidated fringe therapies.