Differential diagnosis includes ruling out other causes such as drug-induced conditions, dementia, infections, metabolic disorders, and endocrine disorders. Other psychiatric disorders must then be ruled out. In delusional disorder, mood symptoms tend to be brief or absent, and unlike schizophrenia, delusions are non-bizarre and hallucinations are minimal or absent.

Interviews are important tools to obtain information about the patient's life situation and past history to help make a diagnosis. Clinicians generally review earlier medical records to gather a full history. Clinicians also try to interview the patient's immediate family, as this can be helpful in determining the presence of delusions. The mental status examination is used to assess the patient's current mental condition.

A psychological questionnaire used in the diagnosis of the delusional disorder is the Peters Delusion Inventory (PDI) which focuses on identifying and understanding delusional thinking. However, this questionnaire is more likely used in research than in clinical practice.

In terms of diagnosing a non-bizarre delusion as a delusion, ample support should be provided through fact checking. In case of non-bizarre delusions, Psych Central notes, "All of these situations could be true or possible, but the person suffering from this disorder knows them not to be (e.g., through fact-checking, third-person confirmation, etc.)."

Psychosis is first and foremost a diagnosis of exclusion. So a new-onset episode of psychosis "cannot" be considered a symptom of a psychiatric disorder until other relevant and known causes of psychosis are properly excluded, or ruled out. Many clinicians improperly perform, or entirely miss this step, introducing avoidable diagnostic error and misdiagnosis.

An initial assessment includes a comprehensive history and physical examination by a physician, psychiatrist, psychiatric nurse practitioner or psychiatric physician assistant. Biological tests should be performed to exclude psychosis associated with or caused by substance use, medication, toxins, surgical complications, or other medical illnesses.

Delirium should be ruled out, which can be distinguished by visual hallucinations, acute onset and fluctuating level of consciousness, indicating other underlying factors, including medical illnesses. Excluding medical illnesses associated with psychosis is performed by using blood tests to measure:

- Thyroid-stimulating hormone to exclude hypo- or hyperthyroidism,

- Basic electrolytes and serum calcium to rule out a metabolic disturbance,

- Full blood count including ESR to rule out a systemic infection or chronic disease, and

- Serology to exclude syphilis or HIV infection.

Other investigations include:

- EEG to exclude epilepsy, and an

- MRI or CT scan of the head to exclude brain lesions.

Because psychosis may be precipitated or exacerbated by common classes of medications, medication-induced psychosis should be ruled out, particularly for first-episode psychosis. Both substance- and medication-induced psychosis can be excluded to a high level of certainty, using a

- Urinalysis and a

- Full serum toxicology screening.

Because some dietary supplements may also induce psychosis or mania, but cannot be ruled out with laboratory tests, a psychotic individual's family, partner, or friends should be asked whether the patient is currently taking any dietary supplements.

Common mistakes made when diagnosing people who are psychotic include:

- Not properly excluding delirium,

- Not appreciating medical abnormalities (e.g., vital signs),

- Not obtaining a medical history and family history,

- Indiscriminate screening without an organizing framework,

- Missing a toxic psychosis by not screening for substances "and" medications

- Not asking family or others about dietary supplements,

- Premature diagnostic closure, and

- Not revisiting or questioning the initial diagnostic impression of primary psychiatric disorder.

Only after relevant and known causes of psychosis are excluded, a mental health clinician may make a psychiatric differential diagnosis using a person's family history, incorporating information from the person with psychosis, and information from family, friends, or significant others.

Types of psychosis in psychiatric disorders may be established by formal rating scales. The Brief Psychiatric Rating Scale (BPRS) assesses the level of 18 symptom constructs of psychosis such as hostility, suspicion, hallucination, and grandiosity. It is based on the clinician's interview with the patient and observations of the patient's behavior over the previous 2–3 days. The patient's family can also answer questions on the behavior report. During the initial assessment and the follow-up, both positive and negative symptoms of psychosis can be assessed using the 30 item Positive and Negative Symptom Scale (PANSS).

Some critical psychiatrists criticize the practice of defining one and the same belief as normal in one culture and pathological in another culture for cultural essentialism. They argue that since cultural influences are mixed, including not only parents and teachers but also peers, friends, books and the internet, and the same cultural influence can have different effects depending on earlier cultural influences, the assumption that culture can be boiled down to a few traceable, distinguishable and statistically quantifiable factors and that everything that does not fall in those factors must be biological, is not a justified assumption. Other critical psychiatrists argue that just because a person's belief is unshaken by one influence does not prove that it would remain unshaken by another. For example, a person whose beliefs are not changed by verbal correction from a psychiatrist, which is how delusion is usually diagnosed, may still change his or her mind when observing empirical evidence, only that psychiatry rarely if ever present patients with such situations.

Psychosis as a symptom of a psychiatric disorder is first and foremost a diagnosis of exclusion. So a new-onset episode of psychosis "cannot" be considered to be a symptom of a psychiatric disorder until other relevant and known medical causes of psychosis are excluded, or ruled out. Many clinicians improperly perform, or entirely miss this step, introducing avoidable diagnostic error and misdiagnosis.

An initial assessment includes a comprehensive history and physical examination. Although no biological laboratory tests exist which confirm schizoaffective disorder, biological tests should be performed to exclude psychosis associated with or caused by substance use, medications, toxins or poisons, surgical complications, or other medical illnesses. Since non-medical mental health practitioners are not trained to exclude medical causes of psychosis, people experiencing psychosis should be referred to an emergency department or hospital.

Delirium should be ruled out, which can be distinguished by visual hallucinations, acute onset and fluctuating level of consciousness, indicating other underlying factors which includes medical illnesses. Excluding medical illnesses associated with psychosis is performed by using blood tests to measure:

- Thyroid-stimulating hormone to exclude hypo- or hyperthyroidism,

- Basic electrolytes and serum calcium to rule out a metabolic disturbance,

- Full blood count including ESR to rule out a systemic infection or chronic disease, and

- Serology to exclude syphilis or HIV infection.

Other investigations which may be performed include:

- EEG to exclude epilepsy, and an

- MRI or CT scan of the head to exclude brain lesions.

Blood tests are not usually repeated for relapse in people with an established diagnosis of schizoaffective disorder, unless there is a specific "medical" indication. These may include serum BSL if olanzapine has previously been prescribed, thyroid function if lithium has previously been taken to rule out hypothyroidism, liver function tests if chlorpromazine has been prescribed, CPK levels to exclude neuroleptic malignant syndrome, and a urinalysis and serum toxicology screening if substance use is suspected. Assessment and treatment may be done on an outpatient basis; admission to an inpatient facility is considered if there is a risk to self or others.

Because psychosis may be precipitated or exacerbated by common classes of psychiatric medications, such as antidepressants, ADHD stimulant medications, and sleep medications, prescribed medication-induced psychosis should be ruled out, particularly for first-episode psychosis. This is an essential step to reduce diagnostic error and to evaluate potential medication sources of further patient harm. Regarding prescribed medication sources of patient harm, Yale School of Medicine Professor of Psychiatry Malcolm B. Bowers, Jr, MD wrote:

Illicit drugs aren't the only ones that precipitate psychosis or mania—prescribed drugs can too, and in particular, some psychiatric drugs. We investigated this and found that about 1 in 12 psychotic or manic patients in an inpatient psychiatric facility are there due to antidepressant-induced psychosis or mania. That's unfortunate for the field [of psychiatry] and disastrous for some of our patients.

Substance-induced psychosis should also be ruled out. Both substance- and medication-induced psychosis can be excluded to a high level of certainty while the person is psychotic, typically in an emergency department, using both a

- Broad spectrum urine toxicology screening, and a

- Full serum toxicology screening (of the blood).

Some dietary supplements may also induce psychosis or mania, but cannot be ruled out with laboratory tests. So a psychotic person's family, partner, or friends should be asked whether he or she is currently taking any dietary supplements.

Common mistakes made when diagnosing psychotic patients include:

- Not properly excluding delirium,

- Missing a toxic psychosis by not screening for substances "and" medications,

- Not appreciating medical abnormalities (e.g., vital signs),

- Not obtaining a medical history and family history,

- Indiscriminate screening without an organizing framework,

- Not asking family or others about dietary supplements,

- Premature diagnostic closure, and

- Not revisiting or questioning the initial diagnostic impression of primary psychiatric disorder.

Only after these relevant and known causes of psychosis have been ruled out can a psychiatric differential diagnosis be made. A mental health clinician will incorporate family history, observation of a psychotic person's behavior while the person is experiencing active symptoms, to begin a psychiatric differential diagnosis. Diagnosis also includes self-reported experiences, as well as behavioral abnormalities reported by family members, friends, or significant others. Mistakes in this stage include:

- Not screening for dissociative disorders. Dissociative identity disorder and psychotic symptoms in schizoaffective disorder have considerable overlap, yet a different overall treatment approach.

The modern definition and Jaspers' original criteria have been criticised, as counter-examples can be shown for every defining feature.

Studies on psychiatric patients show that delusions vary in intensity and conviction over time, which suggests that certainty and incorrigibility are not necessary components of a delusional belief.

Delusions do not necessarily have to be false or 'incorrect inferences about external reality'. Some religious or spiritual beliefs by their nature may not be falsifiable, and hence cannot be described as false or incorrect, no matter whether the person holding these beliefs was diagnosed as delusional or not.

In other situations the delusion may turn out to be true belief. For example, in delusional jealousy, where a person believes that their partner is being unfaithful (and may even follow them into the bathroom believing them to be seeing their lover even during the briefest of partings), it may actually be true that the partner is having sexual relations with another person. In this case, the delusion does not cease to be a delusion because the content later turns out to be verified as true or the partner actually chose to engage in the behavior of which they were being accused.

In other cases, the delusion may be assumed to be false by a doctor or psychiatrist assessing the belief, because it "seems" to be unlikely, bizarre or held with excessive conviction. Psychiatrists rarely have the time or resources to check the validity of a person’s claims leading to some true beliefs to be erroneously classified as delusional. This is known as the Martha Mitchell effect, after the wife of the attorney general who alleged that illegal activity was taking place in the White House. At the time, her claims were thought to be signs of mental illness, and only after the Watergate scandal broke was she proved right (and hence sane).

Similar factors have led to criticisms of Jaspers' definition of true delusions as being ultimately 'un-understandable'. Critics (such as R. D. Laing) have argued that this leads to the diagnosis of delusions being based on the subjective understanding of a particular psychiatrist, who may not have access to all the information that might make a belief otherwise interpretable. R. D. Laing's hypothesis has been applied to some forms of projective therapy to "fix" a delusional system so that it cannot be altered by the patient. Psychiatric researchers at Yale University, Ohio State University and the Community Mental Health Center of Middle Georgia have used novels and motion picture films as the focus. Texts, plots and cinematography are discussed and the delusions approached tangentially. This use of fiction to decrease the malleability of a delusion was employed in a joint project by science-fiction author Philip Jose Farmer and Yale psychiatrist A. James Giannini. They wrote the novel "Red Orc's Rage", which, recursively, deals with delusional adolescents who are treated with a form of projective therapy. In this novel's fictional setting other novels written by Farmer are discussed and the characters are symbolically integrated into the delusions of fictional patients. This particular novel was then applied to real-life clinical settings.

Another difficulty with the diagnosis of delusions is that almost all of these features can be found in "normal" beliefs. Many religious beliefs hold exactly the same features, yet are not universally considered delusional. These factors have led the psychiatrist Anthony David to note that "there is no acceptable (rather than accepted) definition of a delusion." In practice, psychiatrists tend to diagnose a belief as delusional if it is either patently bizarre, causing significant distress, or excessively pre-occupying the patient, especially if the person is subsequently unswayed in belief by counter-evidence or reasonable arguments.

It is important to distinguish true delusions from other symptoms such as anxiety, fear, or paranoia. To diagnose delusions a mental state examination may be used. This test includes appearance, mood, affect, behavior, rate and continuity of speech, evidence of hallucinations or abnormal beliefs, thought content, orientation to time, place and person, attention and concentration, insight and judgment, as well as short-term memory.

Johnson-Laird suggests that delusions may be viewed as the natural consequence of failure to distinguish conceptual relevance. That is, the person takes irrelevant information and puts it in the form of disconnected experiences, then it is taken to be relevant in a manner that suggests false causal connections. Furthermore, the person takes the relevant information, in the form of counterexamples, and ignores it.

A challenge in the treatment of delusional disorders is that most patients have limited insight, and do not acknowledge that there is a problem. Most patients are treated as out-patients, although hospitalization may be required in some cases if there is a risk of harm to self or others. Individual psychotherapy is recommended rather than group psychotherapy, as patients are often quite suspicious and sensitive. Antipsychotics are not well tested in delusional disorder, but they do not seem to work very well, and often have no effect on the core delusional belief. Antipsychotics may be more useful in managing agitation that can accompany delusional disorder. Until further evidence is found, it seems reasonable to offer treatments which have efficacy in other psychotic disorders.

Psychotherapy for patients with delusional disorder can include cognitive therapy which is conducted with the use of empathy. During the process, the therapist can ask hypothetical questions in a form of therapeutic Socratic questioning. This therapy has been mostly studied in patients with the persecutory type. The combination of pharmacotherapy with cognitive therapy integrates treating the possible underlying biological problems and decreasing the symptoms with psychotherapy as well. Psychotherapy has been said to be the most useful form of treatment because of the trust formed in a patient and therapist relationship.

Supportive therapy has also been shown to be helpful. Its goal is to facilitate treatment adherence and provide education about the illness and its treatment.

Furthermore, providing social skills training has helped many persons. It can promote interpersonal competence as well as confidence and comfort when interacting with those individuals perceived as a threat.

Insight-oriented therapy is rarely indicated or contraindicated; yet there are reports of successful treatment. Its goals are to develop therapeutic alliance, containment of projected feelings of hatred, impotence, and badness; measured interpretation as well as the development of a sense of creative doubt in the internal perception of the world. The latter requires empathy with the patient's defensive position.

In 2013, the American Psychiatric Association released the fifth edition of the DSM (DSM-5). To be diagnosed with schizophrenia, two diagnostic criteria have to be met over much of the time of a period of at least one month, with a significant impact on social or occupational functioning for at least six months. The person had to be suffering from delusions, hallucinations, or disorganized speech. A second symptom could be negative symptoms, or severely disorganized or catatonic behaviour. The definition of schizophrenia remained essentially the same as that specified by the 2000 version of DSM (DSM-IV-TR), but DSM-5 makes a number of changes.

- Subtype classifications – such as catatonic and paranoid schizophrenia – are removed. These were retained in previous revisions largely for reasons of tradition, but had subsequently proved to be of little worth.

- Catatonia is no longer so strongly associated with schizophrenia.

- In describing a person's schizophrenia, it is recommended that a better distinction be made between the current state of the condition and its historical progress, to achieve a clearer overall characterization.

- Special treatment of Schneider's first-rank symptoms is no longer recommended.

- Schizoaffective disorder is better defined to demarcate it more cleanly from schizophrenia.

- An assessment covering eight domains of psychopathology – such as whether hallucination or mania is experienced – is recommended to help clinical decision-making.

The ICD-10 criteria are typically used in European countries, while the DSM criteria are used in the United States and to varying degrees around the world, and are prevailing in research studies. The ICD-10 criteria put more emphasis on Schneiderian first-rank symptoms. In practice, agreement between the two systems is high. The current proposal for the ICD-11 criteria for schizophrenia recommends adding self-disorder as a symptom.

If signs of disturbance are present for more than a month but less than six months, the diagnosis of schizophreniform disorder is applied. Psychotic symptoms lasting less than a month may be diagnosed as brief psychotic disorder, and various conditions may be classed as psychotic disorder not otherwise specified, while schizoaffective disorder is diagnosed if symptoms of mood disorder are substantially present alongside psychotic symptoms. If the psychotic symptoms are the direct physiological result of a general medical condition or a substance, then the diagnosis is one of a psychosis secondary to that condition. Schizophrenia is not diagnosed if symptoms of pervasive developmental disorder are present unless prominent delusions or hallucinations are also present.

Schizophrenia is diagnosed based on criteria in either the American Psychiatric Association's (APA) fifth edition of the "Diagnostic and Statistical Manual of Mental Disorders" (DSM 5), or the World Health Organization's International Statistical Classification of Diseases and Related Health Problems (ICD-10). These criteria use the self-reported experiences of the person and reported abnormalities in behavior, followed by a clinical assessment by a mental health professional. Symptoms associated with schizophrenia occur along a continuum in the population and must reach a certain severity and level of impairment, before a diagnosis is made. As of 2013 there is no objective test.

Because of reduced levels of trust, there can be challenges in treating PPD. However, psychotherapy, antidepressants, antipsychotics and anti-anxiety medications can play a role when an individual is receptive to intervention.

The most widely used criteria for diagnosing schizoaffective disorder are from the American Psychiatric Association's "Diagnostic and Statistical Manual of Mental Disorders-5".

The DSM-IV schizoaffective disorder definition was plagued by problems of being inconsistently (or unreliably) used on patients; when the diagnosis is made, it doesn't stay with most patients over time; and it has questionable diagnostic validity (that is, it doesn't describe a distinct disorder, nor predict any particular outcome). These problems have been slightly reduced (or "modestly improved") in the DSM-5 according to Carpenter.

When psychotic symptoms are confined to an episode of mania or depression (with or without mixed features), the diagnosis is that of a “psychotic” mood disorder, namely either bipolar disorder or major depression). Only when psychotic states persist in a sustained fashion for two weeks or longer without concurrent affective symptoms is the diagnosis schizoaffective disorder or schizophrenia.

The second cardinal guideline in the DSM-5 diagnosis of schizoaffective disorder is one of timeframe.

These two changes are intended by the DSM-5 workgroup to accomplish two goals:

- Increase the diagnosis' consistency (or reliability) when it is used;

- Significantly decrease the overall use of the schizoaffective disorder diagnosis.

If the schizoaffective diagnosis is used less often, other diagnoses (like psychotic mood disorders and schizophrenia) are likely to be used more often; but this is hypothetical until real-world data arrive. Validity problems with the diagnosis remain and await further work in the fields of psychiatric genetics, neuroimaging, and cognitive science that includes the overlapping fields of cognitive, affective, and social neuroscience, which may change the way schizoaffective disorder is conceptualized and defined in future versions of the DSM and ICD.

Medications for schizophrenia are often used, especially when positive symptoms are present. Both first-generation antipsychotics and second-generation antipsychotics may be useful. Cognitive behavioral therapy has also been used.

The evidence for the effectiveness of early interventions to prevent psychosis appeared inconclusive. Whilst early intervention in those with a psychotic episode might improve short term outcomes, little benefit was seen from these measures after five years. However, there is evidence that cognitive behavioral therapy (CBT) may reduce the risk of becoming psychotic in those at high risk, and in 2014 the UK National Institute for Health and Care Excellence (NICE) recommended preventive CBT for people at risk of psychosis.

In patients suffering from schizophrenia, grandiose and religious delusions are found to be the least susceptible to cognitive behavioral interventions. Cognitive behavioral intervention is a form of psychological therapy, initially used for depression, but currently used for a variety of different mental disorders, in hope of providing relief from distress and disability. During therapy, grandiose delusions were linked to patients' underlying beliefs by using inference chaining. Some examples of interventions performed to improve the patient's state were focus on specific themes, clarification of neologisms, and thought linkage. During thought linkage, the patient is asked repeatedly by the therapist to explain his/her jumps in thought from one subject to a completely different one.

Patients suffering from mental disorders that experience grandiose delusions have been found to have a lower risk of having suicidal thoughts and attempts.

Studies suggest that the prevalence of paraphrenia in the elderly population is around 2-4%.

In the DSM-IV-TR, paranoia is diagnosed in the form of:

- paranoid personality disorder ()

- paranoid schizophrenia (a subtype of schizophrenia) ()

- the persecutory type of delusional disorder, which is also called "querulous paranoia" when the focus is to remedy some injustice by legal action. ()

According to clinical psychologist P. J. McKenna, "As a noun, paranoia denotes a disorder which has been argued in and out of existence, and whose clinical features, course, boundaries, and virtually every other aspect of which is controversial. Employed as an adjective, paranoid has become attached to a diverse set of presentations, from paranoid schizophrenia, through paranoid depression, to paranoid personality—not to mention a motley collection of paranoid 'psychoses', 'reactions', and 'states'—and this is to restrict discussion to functional disorders. Even when abbreviated down to the prefix para-, the term crops up causing trouble as the contentious but stubbornly persistent concept of paraphrenia".

At least 50% of the diagnosed cases of schizophrenia experience delusions of reference and delusions of persecution. Paranoia perceptions and behavior may be part of many mental illnesses, such as depression and dementia, but they are more prevalent in three mental disorders: paranoid schizophrenia, delusional disorder (persecutory type), and paranoid personality disorder.

While paraphrenia can occur in both men and women, it is more common in women, even after the difference has been adjusted for life expectancies. The ratio of women with paraphrenia to men with paraphrenia is anywhere from 3:1 to 45:2

Routine medical assessments are often prescribed to rule-out or identify a somatic cause for bipolar I symptoms. These tests can include ultrasounds of the head, x-ray computed tomography (CAT scan), electroencephalogram, HIV test, full blood count, thyroid function test, liver function test, urea and creatinine levels and if patient is on lithium, lithium levels are taken. Drug screening includes recreational drugs, particularly synthetic cannabinoids, and exposure to toxins.

According to the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, 5th Edition), Cotard delusion falls under the category of somatic delusions, those that involve bodily functions or sensations. (Citation needed. DSM-5 does not specifically reference Cotard syndrome.)

There are no further diagnostic criteria for Cotard syndrome within the DSM-5, and identification of the syndrome relies heavily on clinical interpretation.

Cotard delusion should not be confused with Delusional Disorders as defined by the DSM-5, which involve a different spectrum of symptoms that are less severe and have lesser detrimental effect on functioning.

Diagnosis of cyclothymia is difficult for a number of reasons. The depressive-dysthymic episode of cyclothymia is also a diagnostic feature of many disorders, including adjustment disorders, personality disorders, psychotic disorders, and other mood disorders. Since depression can be triggered or exacerbated by life events and circumstances, the diagnosing clinician must determine when it is an acceptable response and when it is pathological.

Symptoms described in the hypomanic episode are also commonly associated with ADHD, such as increased energy, distractibility and impulsive or risk-seeking behavior. This is of particular concern in child psychiatry because symptoms, especially hyperactivity, may be counted twice toward both disorders or may inflate the prevalence of ADHD.

While childhood ADHD often presents with hyperactivity, adult ADHD often does not. The unstable lifestyle often found both in people with ADHD and in those with cyclothymia can cause problems for differential diagnosis. Important distinguishing factors include that ADHD is characterized mainly by problems with concentration and memory, while cyclothymia mainly by periods of elevated self-confidence and elation.

Whether subtypes of bipolar disorder, such as cyclothymia truly represent separate disorders or are part of a unique bipolar spectrum is still debated in research. Cyclothymia is typically not described in research studies or diagnosed in clinical settings, making it less recognizable and less understood by professionals. This absence of cyclothymia in research and clinical settings suggests that cyclothymia is either being diagnosed as another mood disorder or as a non-affective psychiatric disorder or not coming to scientific or clinical attention due to a lack of diagnostic clarity or because the nature of cyclothymia is still highly contested. Additionally, the current diagnostic criterion for cyclothymia emphasizes that symptoms are persistent, which suggests that they are enduring traits rather than a psychological state, thus, it has been argued that it should be diagnosed as a personality disorder. Since the symptoms tend to overlap with personality disorders, the validity and distinction between these two diagnostic categories has been debated.

Lastly, the tendency of cyclothymia to be comorbid with other mental disorders makes diagnosis difficult. These issues prevent consensus on the definition of cyclothymia and its relationship with other mental disorders among researchers and clinicians. This lack of consensus on an operational definition and symptom presentation is especially pronounced with children and adolescents because the diagnostic criteria have not been adequately adapted to take into account their developmental level. However, there has been a shift from categorical models of bipolar related disorders toward a dimensional model, which is intended to address some of these issues.

This disorder is common in the relatives of patients with bipolar disorder, and some individuals with cyclothymia eventually develop bipolar disorder themselves. It may persist throughout adult life, cease temporarily or permanently, or develop into more severe mood swings, meeting the criteria for bipolar disorder or recurrent depressive disorder in some cases.

Because it is a rare and poorly understood condition, there is no definitive way to diagnose the Capgras delusion. Diagnosis is primarily made on psychological evaluation of the patient, who is most likely brought to a psychologist's attention by a family member or friend believed to be an imposter by the person under the delusion.

Research suggests that the severity of the delusions of grandeur is directly related to a higher self-esteem in individuals and inversely related to any individual’s severity of depression and negative self-evaluations. Lucas "et al." found that there is no significant gender difference in the establishment of grandiose delusion. However, there is a claim that ‘the particular component of Grandiose delusion’ may be variable across both genders. Also, it had been noted that the presence of GDs in people with at least grammar or high school education was greater than lesser educated persons. Similarly, the presence of grandiose delusions in individuals who are the eldest is greater than in individuals who are the youngest of their siblings.

Accurately assessing for a specific Depressive Disorder diagnosis requires an expenditure of time that is deemed unreasonable for most primary care physicians. For this reason, physicians often use this code as a proxy for a more thorough diagnosis. There is concern that this may lead to a "wastebasket" mindset for certain disorders. In addition reimbursement through Medicare may be lower for certain non specific diagnosis.

The attribution model has been well talked about regarding paranoid or delusional individuals. The idea is that they like to assign issues to external events. A motivation behind this characteristic may involve the need for that person to develop a better self-image and maintain self-confidence. There have been debates about whether or not paranoid individuals are more likely to have a low or high self-perception, and results have been generated for both of these hypotheses. Researchers have made a distinction between positive self-esteem and negative self-esteem revealing that paranoid delusional individuals have more of a negative self-evaluation.

A 2012 paper suggested that, when compared with experiences today, psychiatric conditions associated with psychotic spectrum symptoms may be possible explanations for some revelatory driven experiences and activities such as those of Abraham, Moses, Jesus, and Saint Paul. However, the paper admits that the study was not aimed to deny supernatural elements, nor was it conclusive on whether their experiences were delusional in part or not at all.

When the focus is to remedy some injustice by legal action, they are sometimes called "querulous paranoia".

In cases where reporters of stalking behavior have been judged to be making false reports, a majority of them were judged to be delusional.