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An Introduction

This volume is designed to review information about delusions and try to come up with hypothesis that may explain delusions from an evolutionary point of view. But why would I do this? I have practised clinical psychiatry for over 25 years and have found the current definition of delusions to be very inconsistent, in ways that will be gone through in the book. My hope is that I can provide a conceptual framework from which we can define delusions anew and use this to aid further research.


My focus will be evolutionary, in that I am seeking to determine if there is a function behind delusions, that could have operated via the different evolutionary mechanisms. This is partly because psychiatric diagnosis is so unreliable and to move away from talking about pathology and to focus the discussion on function. My other focus will essentially be clinical, to see if a more clinically useful definition can be found, which relies less on clinical impressions and more on objective evidence.


Delusions are a very common psychopathological symptom and can be found in a variety of conditions ranging from Alzheimer’s to schizophrenia, to mood disorders; they can appear to arise in neurotic illness and are sometimes hard to differentiate from them. Currently the classic descriptive psychopathological description of a delusion is “A delusion is a false, unshakeable idea or belief which is out of keeping with the patient’s educational, cultural and social background and held with extraordinary conviction and certainty”, which seems to highlight the disordered experience of reality.


There are alternative definitions of delusions; many of these are based on the work of Jaspers.

  • Jaspers 1959: “A belief held with unusual conviction that is not amenable to logic whose erroneousness is manifestly obvious to others”.

  • Hamilton 1978: “A false, unshakeable belief which arises from internal morbid processes. It is clearly recognizable when it is out of keeping with the patient’s background” · “a fixed, (usually) false or fantastic idea, held in the face of evidence to the contrary, and out of keeping with the patient’s social milieu”.


The concept of delusions has a complex evolution, e.g., German psychiatry has never embraced the distinction of primary and secondary delusions. Language has a role also; for example, the French word ‘delire’ has resulted in emotional concepts being incorporated into the French version of delusions, whereas the Anglo-Saxon version of delusions does not involve such constructs. Some feel that delusions are thoughts that take on a different form from normal thinking, which result in false judgments (as opposed to the content being false), and they are separate from the judgment, it simply ‘uses’ the processes of judgment (Mendes 2004). Here I am trying to find variables that are involved in the concept of delusion somehow, I am furnishing the house as opposed to trying to build it. Due to the complex nature of psychopathology, this will necessarily involve aspects of neurology, psychology, and sociology, all operating on different levels, timescales and probably with interactions and feedback at different points.

About Me

Welcome to this page and together I hope we can study the field of delusions jointly. As you may know, delusions are a very common symptom in the mental health field. I have had an interest in this topic for many years and I decided that it was about time to put some of my thoughts out there.

First a little about me, my name is Dr Syed Shah and I have been working in psychiatry for over 26 years. I have practiced in the UK, New Zealand and Australia with the main areas of my experience covering the main disciplines of psychiatry, e.g., addition, adult mental health, etc.


My interest in delusions took off a long time ago, after years of seeing patients with this symptom. It is a complex area, often dealing with the absurd and other times fading into normality. Where do they come from? Do they always represent illness or do they have a purpose? These and other questions will be looked at in due course, on this website.

Supportive Friend

What is a Delusion?

Subjectively, a delusional individual would feel that a thought, which is considered delusional by observers, is in fact a true belief and not fantasy and will often defend it in the way they would defend other beliefs. Note the term ‘considered delusional by observers’, we, as psychiatrists, judge who is delusional based on our interaction with the patient. The psychiatrist compares what is considered normal, with what the patient presents. But several studies have also shown that ‘delusional scores’ for non-psychiatric and psychiatric populations tend to overlap, e.g., between normal people and those with strong religious beliefs. The Peters Delusional Inventory has been used too and some studies have shown higher scores in the non-psychiatric population (Boyle 2002). Taking this into account, do we see patients as delusional if they are at a certain point on the scale? Do they need to show distress? Or do we focus on the social processes that underlie the dimensions and the decision made by the psychiatrist?


Jaspers believed that delusions were primary phenomena, a symptom which reflected a disordered experience of reality, causing an alteration of how one viewed reality. He also described two forms of delusional thinking (Walker 1991).


  • Primary - where the delusion is not explainable by other psychological events, due to an alteration of personality. There may be four types:

    • Delusional intuition (autochthonous) - ‘out of the blue’, ‘brain wave’, arise fully formed as sudden intuitions, tending to occur in a single stage.

    • Delusional perception - occurs in two stages: there is normal perceptual experience and at some point, in the future there is a delusional interpretation, and usually occurs in the setting of a delusional mood.

    • Delusional atmosphere - a.k.a. delusional mood.

    • Delusional memory - delusions which are remembered as if it happened in the past.


  • Secondary - where mood, hallucinations and other experiences found in the person’s life could be responsible.


It is important to realise there is no empirical evidence for this distinction, and some have argued that the development is understandable in terms of the prevailing culture of the time. Others have said that delusions are present when the features of subjective certainty and incorrigibility are related to events in the external world. Contrary to Schneider’s claim, form can be difficult to detect, and we must consider content (Healy 1990).


Jaspers readily accepted that viewing delusions as irrational, firmly held beliefs had its problems; he realised that illogicality was found in many people and when people had this illogicality pointed out, normal beliefs often remained unaltered. To help distinguish them from normal beliefs, he postulated an alteration of personality had to occur first. He also introduced the criteria of deviance from social norms to distinguish them as abnormal, but this has led to the suggestion that any ideas that are different to the therapist’s could be labelled as delusional (Healy 1990). The conviction with which delusional beliefs are held, even in the face of external evidence to the contrary, was held by Jaspers to be a central feature of delusions; where the need to defend the beliefs comes from a need to prevent a collapse of the individual and is of a different quality than the way you or I would defend beliefs not held by the majority. Although operational criteria have been developed for delusions, Jaspers did not feel that these criteria were sufficient to distinguish delusions from normal thought (Walker 1991). Jaspers thought of delusions as a sign of disease, that delusions indicated insanity and arose from defects in the sensory processes. This then brings up the concept of disease. Is a disease a specific entity waiting to be found? Is disease an absence of normality? If normality is altered in delusions, then what aspect of normality is altered? Delusions as disease is a concept that has been reinforced by the fact that neuroleptics can lead to delusions disappearing. Some say neuroleptics reduce tension, anxiety and induce a sense of indifference in normal people, and argue that mental agitation is predelusional, rather than it being a disease process per se. This is also supported by the non-response of many delusions to neuroleptics (Healy 1990).


Some researchers have classified delusions as a type of belief, designed to help cognitive activity, anxiety, and social contacts. These then would need to be compared with other non-delusional beliefs. There are various factors involved in delusional formation: biological, temperament/personality, maintenance of self-esteem, mood, the search for meaning to explain unusual events. Factors involved in the maintenance of delusions include anything that pushes people away from reality, the provocation of confirmatory behaviour in others and the lowering of a person’s social standing when delusions become obvious to others (Brockington 1991). When we say delusions, what is it that the patient experiences? The authors felt high conviction was frequently present; otherwise there was large variability between people on their delusional components. It was not possible to characterise people and their delusions using these criteria (Garety 1987).


Looking at the Morbid Jealousy Database for case histories from 1942–2002 published in English, highlights diagnostic confusion when it comes to delusions. Cases were classed as delusional (32%), morbid (7%), pathological or as conjugal paranoia. 13% had depression, nine had schizophrenia and about 4% had obsessional jealousy. To be diagnosed with delusional disorder – jealousy type – there must be no significant hallucinations, non-bizarre behaviour with a normal mood in the absence of a medical condition or substance abuse. Once these are considered, only 4% were delusional (Easton 2008), but when loosening these criteria there are higher levels of delusional jealousy (66%) (Easton 2007).

Delusional Characteristics

If normal and abnormal thoughts lie on a continuum then a multidimensional viewpoint seems to serve our needs better. They may help in distinguishing delusions, overvalued ideas and obsessions and changing delusions from an all or nothing event. Kendler proposed five dimensions: conviction in the belief, extension – degree to which delusional beliefs involve other areas of the person’s life, bizarreness, disorganisation, and pressure – degree of preoccupation and concern. These may be independent of each other, and different delusions may lie on differing points of these dimensions. But delusional dimensions are themselves a linguistic invention to describe certain psychological events with a conceptualisation of their own (Garety 1987).


Freeman 2006 used different dimensions:

  • Unfounded: from fantastic ideas to having some truth in it

  • Firmly held: from 100% conviction to believing it occasionally

  • Resistance: refusing alternative explanations to considering alternatives

  • Preoccupying: from thinking about all the time to thinking about it occasionally

  • Distressing: from very distressed to hardly any

  • Social function: isolated to high functioning

  • Personal reference: feels they’re at the centre to be on the margins

Therapy Session
Plausibility & Conviction

How does one decide if a particular thought, idea, etc. is realistic? It has been argued that religious beliefs and other firmly held ideas could well have delusional characteristics – e.g. held with conviction, not amenable to logic – but these ideas certainly aren't considered delusional, even if the people who hold the beliefs are in a minority in the community.

Mary Boyle’s book on schizophrenia challenges the idea that delusional beliefs are held with a conviction that is qualitatively different from other non-delusional beliefs. One study had two jars with a certain proportion of balls in each jar and people were asked to remove a ball at random and to decide which jar they had chosen. In a second condition they were required to state the probability that a particular jar had been chosen. In a subset of delusional patients, the contradictory evidence led them to alter their conclusions faster than controls (Garety 1991). Another study showed reduced conviction in chronically deluded patients after cognitive therapy. Also, conviction has been shown to be less than absolute in other studies, can be altered with alternative explanations and vary between people, within the same individual and between environments. On the other hand, there are studies that show conviction is characteristic of delusions, e.g. 80% of deluded subjects with high levels of conviction in their delusional beliefs (Garety 1987).

What about obsessions and overvalued ideas?

Obsessions are defined as recurrent intrusive thoughts, feelings or ideas that are recognised as coming from themselves. Patients recognise them as senseless. Overvalued ideas are ideas that are pursued beyond the bounds of reason, are associated with strong effect and are like strong political and religious beliefs. These beliefs overlap somewhat with delusions, though by definition they are said to be distinct. Overvalued thoughts’ main difference from delusions lies in their similarity to strong, normal beliefs, whereas delusions are said to be abnormal beliefs as defined by Jaspers (McKenna 1984). Delusional beliefs have been found in OCD. OCD patients can have poor insight with the conviction and fixity varying over time. About a third of patients with OCD believed the feared consequence would happen if rituals weren't followed. Some have argued that the fixity and bizarreness with the lack of insight qualifies the obsession as a delusion. Obsessions can also be bizarre and may be hard to distinguish from schizophrenic bizarreness, and DSM IV has allowed bizarreness as a criterion for OCD. Of those with OCD in the Epidemiological Catchment Area study, about 15% had some form of paranoia (Edgar 1997, Kozak 1994, O’Dwyer 2000, Poyurovsk 2005, Tien 1990).


In essence it can be hard to tell these different types of psychopathologies apart.

Image by Toa Heftiba
Are Delusions a Unity Concept?

They involve many different variables. Firstly the delusional themes can be quite variable, from being jealous that your partner is having an affair, to feeling that someone is in love with you, to paranoia, etc. Second, delusions are characterised along various dimensions. Which raises the question of what combination of dimensions classifies thoughts as delusions. It also raises the possibility that we could have a delusion where only one dimension is at a high level, but the others are at a low level. Thirdly the diagnosis of delusions is a social one, for example involving the social difference between the patient and psychiatrist, that there is a filtering process that screens the delusions as they come to a professional. Fourthly, it seems that the neurological changes that may underlie delusions vary widely, e.g. right hemisphere damage in delusional misidentification syndromes, first rank delusions/anosognosia and the right temporal and parietal cortices, with other evidence implicating the left hemisphere and various subcortical areas. Fifthly, the psychological abnormalities found in delusions, such as jumping to conclusions, are not universally found in delusions, and are also found in the normal. Finally, it is obvious that delusions have a lot of overlap with other types of thought pathology, which might depend on the degree of insight displayed.


Are there ways to measure delusion?


What aspects of current clinical practice lend themselves to objective assessment in relation to delusions? We can observe the mental state and try to understand via empathy and repetition to arrive at a decision on whether delusions are present. One feature of schizophrenia is bizarre delusions but when psychiatrists were asked to rate bizarre and non-bizarre delusions, the agreement levels were low, with kappa values of 0.38 – 0.43 (Mojtabel 1995). There are scales to measure delusions. The Peters Delusional Inventory is a multidimensional measure which is rated by the patient. It yields a total score as well as a score for distress, conviction, and preoccupation (Peters 1999). Another scale for measuring delusional beliefs, is the Brown Assessment of Beliefs Scale (BABS), this is a well-validated and widely used tool (Eisen 1998).

What is the difference between delusions and clinically diagnosed delusions?


It seems to me that there must be processes that filter a delusion so that it becomes a clinically recognised delusion. The point here is that a clinical delusion may not actually be representative of what a delusion truly is as it has been altered by social filtration. Could a strange thought have caught the attention of certain key people over time? Leading them to focus attention on these issues. For example, someone saying that they are Jesus may be more noticeable than someone saying they are a plumber. Additional to social acceptability, distress associated with even so-called normal beliefs may result in a huge number of problems for the patients and so lead the patient into emotional conflict and hence in need of help.


What concepts are assumed by me when I use the term ‘delusion’?


The thought that comes to me is that the concepts that I may or may not use today may not be the same ones that would have been unconsciously used when I was a less experienced psychiatrist. This would probably mean that the conclusions I come to today would be different to those I may have come up with in the past. Hence the behaviour we see in the delusional may not necessarily reflect underlying psychopathology. What behaviours am I using to judge someone as delusional? Do I judge it in a similar fashion to other professionals? As I considered other areas of the mental state exam, I realised that my thoughts fell into a group that is best defined as signs of mental illness, i.e., features that are found on examination of the patient. In other words, I did not consciously use delusions in any way apart from looking for what was considered abnormal according to the psychiatric texts. I certainly considered them abnormal, but this attitude has been significantly modified as the years have gone by. I now feel that ‘extreme beliefs’ are not necessarily indicative of mental illness and there is considerable evidence of delusional-like behaviour in non-clinical populations. 

Cultural, Evolutionary & Psychological Musings on Delusions

Delusions are associated with individual psychological differences, with there being evidence that the information we learn culturally is filtered by our individual biases. If a person has several hypotheses they must choose from, their responses may be available to others. Also, it seems that the harder a category is to learn, the more data and time is needed for learning. And the less likely it is to be considered in the first place and as the generations pass the less likely we are to see it represented, i.e., concepts with higher probability are more easily learnt and get passed. Also, as an aside, some generations seem to choose hypotheses that are far from the most probable, which links into the topic of creativity (Griffiths 2008).


Could the above reasoning influence the development and transmission of delusions? If we consider folie a deux, the secondarily affected delusional patient will have chosen an explanation based on the delusions of the primary case. If the probability of a hypothesis chosen by the delusional person is low, would it be harder to learn by others and hence less likely to be passed on? This would fit in with the low frequency of folie delusions. So is the social transmission of delusions the defining feature of folie delusions, whereas the lack of transmission a reflection of other delusional types? The trouble here is that others may well believe in non-folie delusions. So could folie delusions represent a subset of ‘transmitted’ delusions as opposed to simply being a collection of features that just happen to be interesting to some people? Could the conditional probability that a delusion is true given the data serve as an indicator of ‘cultural reality’? In that the delusions represent ‘reality’ as filtered by cultural norms and evolutionary priorities, and hence those delusions with a low probability represent ‘unreality’ and hence be discarded. If the process of determining probabilities is altered, than low probability hypotheses may be perceived as having a higher probability of occurrence.


Our conscious experiences, e.g. emotions and nervous, interact together and we may respond to a set of meaningful collective experiences, as recognised by the community. These experiences will vary with culture and time and may even have their own representations neurologically. So, delusions occur within these experiences and to fully understand them we need to understand what they mean in the local culture. This of course says that delusions cannot be fully understood from a neurological or psychological point of view (Turner 2008).


Now there is evidence that our visual system is altered in delusions, specifically assessed by the Visual Scan Path technique (see later) and there is evidence that the culture in which we grew up can alter visual perception. By using the Frame Line Test, participants are presented with a square with a vertical line in it and they then must draw the line, either to the same length (so ignoring context) or to draw it in relation to the box (so using context). Those in western countries where individualism is favoured tend to do better with drawing the line to the correct length but not so good with drawing a line in relation to the box, while those in eastern countries where collectivism is favoured show the opposite pattern; so cultural context has altered the visual perception of the line and the box. This brings into question the cross-cultural validity of neuroscientific data in the study of delusions (Chiao 2008).


Evolution has been described as the transfer of information, e.g. protein structure, behavioural techniques, etc. (Jablonka 2005). This information transfer will result in changes to genes and phenotype as time goes by. Could we apply this concept of information to delusions? If so than what kind of information is being transmitted? So, let’s speculate possible functions of the different types of delusions.


  • Paranoia: Humans come across aggressive situations that we must deal with. Those who are successful in aggressive situations may be more likely to survive than those who are not successful at such behaviours. Possible functions fulfilled could be:

    1. Natural selection as they survive

    2. Sexual selection as they are around to mate

    3. Kinship via providing protection and resources

    4. Pathogen avoidance by removing infected people


  1. Delusional jealousy: This might increase the chances of getting and keeping a mate and hence having children, i.e. sexual selection.


  • Somatic: Here the person is now reacting to events they perceive are occurring within their own body. The resultant illness behaviour might have the following functions:

    1. Lead to some form of help from the group, enhancing natural selection

    2. Protection from pathogens

    3. Does it provide advertisement of fitness, hence helping sexual selection?


  1. Erotomania: this has an obvious role via sexual selection.


  1. Grandiose: This is where people display high levels of euphoria, happiness, elation, etc. We generally like to be around the company of happy people, maybe such people are more generous.


  1. First rank delusional symptoms: This involves alteration of where we define the self and not-self. What possible functional role could this have? Does it help assimilate into other cultures by taking on some of their values? Would it be involved in trances and the like, which are part of ancient medical systems and connecting with the ancestors, etc allowing for social function?


  1. Other: In clinical practise we often see delusions with contents that do not fit neatly into the above categories.

    1. Homosexuality – there are patients who are convinced that others view them as a homosexual.

    2. Pregnancy – this is where people feel that they are pregnant.

    3. Zoomorphism – this is where people feel that they have been transformed into animals.

    4. Delusional perception – this is where a normal perception is imbued with a delusional meaning.

    5. Delusional mood – where an individual feels something significant is happening.


Developing delusional behaviours may be modulated by the probability of learning cultural values. If delusions are primarily cultural constructs, then the prevalence of delusions would reflect the probability that people believe the delusional construct. If delusions are primarily evolutionarily based, then we would expect to see long-term changes in frequencies of delusions as natural selection occurs. One aspect of behavioural-genetic coevolution is that we construct habitats that are suitable for us: ‘niche construction’. I wonder if there is something akin to this in the psychological realm. I presume that this would reduce distress/discomfort, etc. Could delusions be a result of a process to achieve relief? Niche construction can involve a manipulation of space, changing the spatial environment which then serves to provide further input and feedback. It may result in the environment/perception/cognitive processing being simplified via the formation of categories and these than inform further thought, etc. Some have suggested that niche construction would alter environments for succeeding generations, who would then make their own changes, and these constantly changing environments would impact on genetic evolution, e.g. we learn cognitive abilities by observation (Wheeler 2008). A cultural change may lead people to behave in certain ways and as time goes by cultural views may encourage genetic changes that allow these features to appear more easily. So that in time it becomes easier to fit into the culture. Now not all behavioural or cultural changes are adaptive, and some may die out as they are not propagated. While others that fit in are propagated and learned by future generations, for example distress caused by fashions, etc. lead men and women to desire a body image that is different to the one they have or not healthy and this may reach delusional proportions. Could a malleable body image help people fit in better with prevailing cultural norms? Could the desire to be thin (females) and muscular (men) be an example of a maladaptive cultural norm, that if it persisted for long enough, would result in genetic changes favouring thinness in females and muscularity in males? (Jablonka 2005)


So could delusions be in part due to a consideration of various alternatives, each with different probabilities of occurrence? When possibilities are considered we see a stage where the probabilities are updated, maybe via the formation of cognitive structures, etc. that then form a new set of inputs that serve to further alter the probabilities of occurrence. This would then eventually result in some outcomes being deemed more probable. The information processing differences that are found in the delusional may serve to bias the whole developmental processes onto an ‘illness’ pathway, with some of this bias coming from the formation of abnormal cognitive structures. This can occur within the individual, resulting in the delusions, or between individuals. If the people around the delusional person do not have any information processing bias, then presumably they would evaluate culturally relevant information in a way where the updated probabilities form cognitive structures that guide further evaluation along a more culturally relevant path.


Current criterion says that a delusion is not in keeping with cultural background. This means that social norms can decide what is a delusion, but this works against novel ideas from people who challenge the status quo. Some have claimed that delusional patients being unable to convince others of the truth of their delusions, distinguishes them from normality, but this becomes a circular argument as we as professionals deliberately do not allow ourselves to be influenced. How can a psychiatrist know the patient and their background and decide that something is delusional using their own experiences as a guide (Boyle 2002).


This cultural view of delusions may say something about computer and internet-related delusions appearing recently. There are online communities relating to mental health, e.g. mind control, providing a space for like-minded people, with some describing their delusions in terms of transmitters, chips and radiation. One case felt that he was a character in a computer game (Forsyth 2001). A 27-year-old male felt that his life was controlled by the internet (Tan 1997). In India a 31-year-old male felt his sister-in-law was controlling him via the internet and computer. With belief modification, as he had no concept of how the internet and computers worked, the belief had gone in about three weeks. The authors felt that ignorance and fear of new technology caused the delusion (Harpreet 2002). In general, some feel that this is a new type of delusion, others that it is an expression of cultural changes (Lerner 2006). Do these delusions come in the form we expect of delusions? With the content simply being filled in by the brain (Bell 2005).


Social failure - A fascinating account of delusions views them as adaptive social mechanisms to combat social failures, which can be so damaging that some people use self-deception to tackle them. Interestingly anosognosia, where people deny their disability, may be associated with people who use denial regularly as part of their premorbid personality (Heilman 1998). This loss of function would be a source of social failure and potentially grounds for delusional behaviour designed to regain social resources.


Low self-esteem - It has been suggested that delusions, especially paranoid delusions, protect against the development of low self-esteem. One study found that as conviction drops with CBT, the scores on Beck’s Depression Inventory also drop (Chadwick 1994). The delusional may have improved self-esteem, as sense is made of the environment (Sims 1993). The actively delusional had lower covert self-esteem but there was no difference in overt self-esteem, supporting the view that persecutory delusions help to maintain self-esteem (McKay 2007). Delusional patients make external attributions for negative events, presumably to avoid conflicts within themselves, but this is also found in the general population (Bruce 1999).


Let’s consider hypochondriacal/somatic delusions. The person develops symptoms which they think are due to physical illness; they then present to physicians, who then proceed to do physical examinations and tests to find an explanation. This can reinforce the notion that there is a physical disorder. But when no physical disorder is found, this can frustrate the patient and may lead to greater health-seeking behaviour. This can lead to an angry patient who can’t understand their symptoms and frustrated doctors who can’t find any explanations. Hence a psychiatric referral is made, which is often resented by the patient and the anxiety, shame, depression, constant preoccupation, interruption to normal social processes, etc. can lead to a pre-delusional state. The stronger we identify with illness, the more likely we are to suffer some detriment, and this leads us to experience a range of psychological problems, such as denial, etc. We all have a certain concept of illness, against which we review a vast array of psychosocial features, and it is the result that we take to the health professional. This professional socially interacts with the patient and comes to a decision about diagnosis, treatment, etc. But the illness behaviour needs to be understood from the personal point of view (e.g., consequences, functional changes, changes to others, etc.), from a familial point of view as family influences development of illness behaviour, and from a wider social perspective (on what symptoms are acceptable, what others feel is proper behaviour). Could this explain the development of somatic delusions? (Sims 1993)


Could we look at delusions in a more functional way? Let’s stay with illness behaviour. Today with proper medical care, illness behaviour has become more adaptive, as we are more likely to get relief from suffering. So, is there now a different reason why illness behaviour is adaptive today, as opposed to that which were more prominent in the past? Because in our evolutionary past, health care was presumably rudimentary, eliciting help to deal with health issues may have gained greater prominence as modern medicine developed, masking other functions of illness behaviour somewhat. Stigmatisation would have raised the inclusive fitness of those doing the stigmatising by avoiding those who are disordered in some way, but it is conceivable that other evolutionary processes may have operated to prevent this reduction in fitness potential. Stabilisation of social groupings may occur with illness behaviour, in that those with similar problems join into a more accepting social group. How would this stabilisation have appeared, reduced intra-group conflict, or provided learning for other members of the group to avoid a similar fate? The question then arises of how someone who is highly convinced, distressed, etc. by the illness behaviour, could have an enhanced inclusive fitness. This social stabilisation has been reflected in some ancient systems of health care and, even today, there are some who feel medicine helps to provide a degree of social control, which is most obvious when professionals and patients disagree.


Finally, when it comes to the data I collected, I searched CKN, google scholar, pubmed, medline and manually searched print journals for various variables on the different delusional types. More details will be found in each section, but I would collect data on age, gender, marital status, employment status, presence of a medical history, presence of a psychiatric history, a family history of psychiatric illness, presence of psychiatric treatment and the response to such treatment, the presence of other delusional types, presence of hallucinations, the number of children and the binary presence of children, the number of siblings, and the duration of the delusions.


As part of this process, this volume reviews many studies, with differing methodologies, statistical approaches, etc. As a result, they cannot be directly compared and hence I have not tried to do so. Such shortcomings essentially mean that this volume is mainly a hypothesis-generating text. I have focused on searching the literature for case reviews, as it provides data on individual level differences and by building up as a large a dataset as possible, it may increase the power to detect possible influences. This of course does not mean that I haven’t tried to extract usable data from various clinical studies, supplemented by the result of other authors’ meta-analysis and systemic reviews. Other problems include the fact that delusional content is poorly described, the differences between delusional patients are not highlighted, social circumstances are not explicitly investigated, various rating scales are used in studies, as are different definitions of a delusion and small sample sizes limit generalisability. Content may indicate different neuropathology and often confounders such as other illnesses, medications, duration of psychotropics, etc., are not controlled for.


Data for dichotomous variables were labelled ‘0’ to indicate absence and ‘1’ to indicate the presence of said variable. When data on the variables were missing from the case reports, I assumed an absence of that variable, e.g., if no information was listed on marital status, I assumed the person was single. When it came missing values, I used STATA multiple imputation commands. I calculated simple descriptive statistical results, such as means, medians, etc, before moving to bivariate analysis such as correlations. Finally, I moved on to simple and then multiple regression methods. Depending on the levels to the dependant variable, I would either use normal regression, logistic or ordinal regression methods.


When it comes to mathematical analysis, several methods will be used and they will be described as and when relevant studies are posted online. For example, multiple regression analyses were performed on the datasets looking at the general direction of the regression coefficients, as opposed to the actual magnitude of them. Some of this information will be shown in tables and others in visual form, to convey as much detail as is possible. I used stepwise forward and stepwise backward regression extensively. Additionally, I used the p-values of a likelihood ratio test to compare ran null models (containing no independent variables) and compare it to a model with one additional variable added. If the p-value is 0.2 or less, I then take that variable forward. I then create a new ‘null’ model containing these variables and compare that to a regression model with one extra variable that did not produce a p-value of 0.2 in the previous round. Again, the likelihood ratio test p-value of 0.2 or less shows that these extra variables might be of importance, and they are added to the ‘null’ model in the next round of testing. I continue this method, until no more variables are significant. The model with the dependant variable and the various significant variables is run and I search for the regression coefficients that have a p of 0.05 or less and report on these. Additionally, I have tried to supplement the analysis with some forms of multivariate analysis, such as factor analysis, etc, so that underlying associations can be investigated.

Poppy Field

In Summary

This limited review of the concept of delusions shows that there is a lot to be desired with the current definition of delusions, highlighting several issues with the concept of delusions. They may be related to a complex interplay of genetics or the wider cultural or social context.


Can they help drive changes in cultural values? Do they serve a function that goes beyond the purely evolutionary?

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