A double blind study is a study in which information that may change the results is kept both from the experimenter and from the participant. This is to keep the results of the study as neutral and unbiased as possible. 

Axis IV records "psychological stressors" or external events that happen in a person's life that causes them to have a psychological problem. Debt, such as the inability to pay hostpital bills, would fall on this axis.

Axis I refers to the principle disorder that needs attention, such as major depressive disorder. Axis II lists any personality disorders that may be causing the problem described in Axis I. An example of a disorder that would be listed under Axis II is paranoid personality disorder. Axis III lists any medical or neurological problems that would be relevant to the patient's psychological problems. An example of a problem that would be listed under Axis III is severe asthma.

Comorbidity occurs when a patient has multiple diagnoses. Comorbidity is common in psychology, in that most patients have multiple diagnoses (e.g., ADHD & ODD) because psychiatric illnesses typically occur together. 

A uniform system for classifying and describing mental disorders has been developed by the American Psychiatric Association. It is called the Diagnostic and Statistical Manual of Mental Disorders.

The American Medical Association maintains the Current Procedural Terminology (CPT) code set, which is a set of codes that describes medical, surgical, and diagnostic services. The International Classification of Disease (ICD) is used to classify diseases and other health problems. Medicare mandates the use of the Healthcare Common Procedure Coding System (HCPCS) for reimbursement. The United States Pharmacopeia (USP) is a compendium of over-the-counter and prescription drugs. 

Insanity is the legal term for a severe mental illness, present at the time a crime was committed, that impaired the defendant's capacity to understand the moral wrong of an act. Insanity is not a medical diagnosis.

Idiocy is any severe mental deficiency present in early childhood. Dementia is a progressive loss of mental function characterized by memory impairment. A psychosis is a mental disorder in which there is a severe loss of contact with reality; it is a common feature of schizophrenia. A neurosis is an unconscious conflict that produces anxiety and leads to the use of defense mechanisms. 

While this may seem like a very broad definition—perhaps classifying deviant behavior rather than a psychological abnormality—psychological abnormality is defined by this crucial element: the individual suffers due to a reocurring problem or disorder. That is, the individual suffers involuntarily at the hands of the disease and has little control of the symptomatic behavior of the illness. They often want to change their illness as opposed to continuing on how they are. 

Common social biases include gender, race, economic class, ethnicity, and many more. Many are not even conscious that they carry these prejudices, and the best we can hope for improvement is to become aware of and change these biases as a society. Current statistics suggest that African-American males are more likely to be diagnostics as psychotic than Caucasian males in instances of subject abuse. This is an example of stereotype and prejudice intersecting professional diagnosis in an increadibly detrimental and socially dangerous manner; even though the individuals may display the same symptoms, they are given different diagnoses.

One of the major practical concerns with giving a person an official diagnosis is that it may become hard for a person to escape the label of that diagnosis. For instance, if a person is diagnosed as schizophrenic, observers may already have a preconceived notion of that person and behave differently towards them. If the diagnosed person sees they are treated as different, this may reinforce negative behaviors and perpetuate the stigma. Even if the person diagnosed as schizophrenic shows positive progress, observers may still have trouble thinking of them as a healthy, stable person.

Because narcissists are so focused on themselves and their own needs, they often neglect the needs of others, sometimes even exploiting these others for their own gain.

Anhedonia is defined as the loss of the ability to experience pleasure. Since Joe is no longer enjoying his hobbies (which are, by definition, activities he likes and enjoys), and spending time with his friends (who are, by definition, people he likes), it is reasonable to assume that he is experiencing some degree of anhedonia.