The development of research into conspiracy theories has been observed within various disciplines, including psychology. The number of psychological studies on conspiracy beliefs (CBs) has been growing systematically for about a dozen years now, but in recent years the trend has intensified. Due to the large number of such studies, conducted in different theoretical and methodological frameworks and using different measurement tools, it might be difficult to make a synthesis of the relevant literature. This was first attempted by Goreis and Voracek (2019), who published in the Frontiers in Psychology journal a systematic review of the psychological literature on CBs, covering the period from the beginning of database records until early 2018. It is also worth mentioning the review by van Mulukom et al. (2022) that summarizes 85 studies (available till March 2021) on antecedents and effects of CBs regarding COVID-19.

The current paper was planned as a continuation of the paper by Goreis and Voracek (2019) in the sense that it provides a review covering the psychological literature on CBs from a subsequent period (2018–2021). Halfway through this period, the COVID-19 pandemic broke out and it became a platform for an explosion of movements based on conspiracy theories, which in turn intensified the interest of researchers in this issue. Thus, it becomes extremely important not only to take a quantitative look at the new research, but also to look at new trends or directions of the analyses. The objective of this review was to summarize the evidence regarding antecedents and consequences of CBs. The significance of our review is based on the systematic approach that was used at all stages of the work. We hope that this paper will provide a useful resource for researchers and practitioners seeking a summary of recent psychological research on CBs.

Conspiracy theories can be defined as explanatory narratives about powerful agents collaborating secretly to achieve malevolent goals (Zonis and Joseph, 1994). The government and global corporations continue to be accused most frequently of conspiracies; however, any group perceived as influential could be charged with conspiracy (Douglas et al., 2019). There are also several terms related to conspiracy theories which should be defined. “Conspiracy beliefs” refer to beliefs in some specific conspiracy theories (Douglas et al., 2019). Specific conspiracy theories are focused on particular events or issues, e.g., the death of Princess Diana (Douglas and Sutton, 2018), the assassination of John F. Kennedy (Calfano, 2020) or 9/11 (Swami et al., 2010). Another term is “conspiracy mentality,” also referred to as “conspiracy ideation” or a tendency toward conspiracy thinking (Douglas et al., 2019). Conspiracy mentality describes the general, fundamental tendency to believe in conspiracies, which creates a monological belief system (Imhoff et al., 2022). It predicts beliefs in specific conspiracy theories—even contradictory (Wood et al., 2012) or fictitious ones (Swami et al., 2011).

Conspiracy theories are widespread in society. They constitute a part of human history but can also adapt to the present times, e.g., in terms of the forms of their dissemination (van Prooijen and Douglas, 2017). Whether we examine accounts of ancient Rome, medieval Europe, or contemporary America, conspiracy theories have inspired millions to take action. In the colonial and early Republic period, Americans feared that Catholics, Jews, Freemasons, Native Americans, and African Americans were conspiring against them. Over time, the list of potential conspirators would be extended to include bankers, rich businessmen and Mormons, and even the U.S. government (Olmstead, 2018; Uscinski, 2018). In a 2013 survey, four percent of polled Americans (12 million people) were found to believe that “shape-shifting reptilian people control our world by taking on human form and gaining political power to manipulate our societies” (Brotherton, 2015). During the 2016 presidential campaign of Donald Trump, many conspiracy theories were propagated, e.g., “Climate change is a hoax perpetrated by the Chinese” or “The pharmaceutical industry hides evidence that vaccines cause autism” (van Prooijen, 2018). According to the recent Eurobarometer data (European Commission, 2021), 28% of European citizens think that some viruses have been produced in government laboratories to diminish people’s freedom, 26% believe that cure for cancer is being hidden from people, whereas 17–18% are unsure whether these statements are true or false.

Conspiracy explanations tend to emerge especially after large-scale distressing events, such as terrorist attacks, economic crises, or epidemics (van Prooijen and Douglas, 2017). Nowadays, conspiracy theories have a greater potential to spread due to the Internet and social media (Connolly et al., 2019; Bangerter et al., 2020). However, not only external circumstances create space for conspiracy theories to spread. Firmly rooted in the literature are also studies presenting specific traits (e.g., cognitive, motivational, psychopathological) of the individual, making the latter more susceptible to conspiracy messages. The primary role of conspiracy theories covers three groups of motives: epistemic (e.g., willingness to understand and need for certainty), existential (e.g., need for security and control), and social (e.g., desire to maintain a positive image of self or in-group; Douglas et al., 2017). Conspiracy theories promise to satisfy important psychological needs and help to manage difficult situations. They make it easier to find meaning in ambiguous events and to deal with insecurity and threats (van Prooijen et al., 2020).

In this systematic review, we sought to identify the main directions and results of the latest research on CBs conducted within the framework of psychological science. We aimed to answer questions about the methodological features of the studies and also to provide a comprehensive overview of their results. We decided to prepare a systematic review with narrative synthesis rather than a meta-analysis because we sought to provide a comprehensive outline of the available research. Moreover, studies on CBs differ significantly in terms of the study designs, measures of CBs, and methods of statistical analysis. The authors often used similar construct (e.g., conspiracy mentality, conspiracy ideation). All the above factors make it very difficult to provide a synthesis of the results, even within a narrower scope. Thus, due to the substantial methodological heterogeneity of the studies, a narrative synthesis was performed.

Goreis and Voracek (2019) conducted the first systematic review devoted to psychological literature on CBs, covering the years from the beginning of database records (i.e., Scopus and Web of Science) until March 2018. Our review is intended to extend their work to cover the years 2018–2021. To do so, we adapted the search strategy and inclusion criteria of the systematic review by Goreis and Voracek (2019) in our review. A search was done on Scopus and Web of Science using the search terms “conspir* OR conspira* ideation OR conspira* belief* OR conspira* theory” and it was limited to the years 2018–2021. No limitation on language was imposed. The search was performed on 17 November 2021.

Initially, 3,504 records were extracted (Web of Science = 2,311, Scopus = 1,193). After duplicates removal, we obtained 2,703 records. The screening process covered the titles and abstracts and it was performed by two researchers (IP and PW) evaluating independently and deciding whether a study met the inclusion criteria using a consensus-based screening process. A study was included if it contained primary empirical data, if specific or general conspiracy belief(s) were measured and if its correlation with at least one other psychological variable was reported. Only articles published in peer-reviewed journals were considered to ensure the quality of the studies. The language of the publication was not an exclusion criterion—one article in German (Baier and Manzoni, 2020) and one in Portuguese (Rezende et al., 2021) were included in the review. One of the articles was published both in English and Portuguese (Rezende et al., 2019a), another one in English and Spanish (Guan et al., 2021). After that, 308 full-text articles were assessed for eligibility, and 274 articles (417 studies) meeting the inclusion criteria were identified and included in the review (see Figure 1). Three reviewers (AOM, PW, and WSJ) extracted data from the studies for further analysis using a form specifically developed for this review. The other two investigators (IP and ATK) verified the data. Any disagreement was resolved by consensus.

All the studies were grouped for the descriptive analysis according to the methodology used (correlational-cross-sectional, correlational-longitudinal, experimental), participants’ characteristics (adults, school-age students, undergraduates), continent of origin, sample size, and CBs measurement tools. For the substantive analysis, the studies were grouped into two partially overlapping groups according to whether their main focus was on the antecedents or consequences of CBs. A full list of papers included in the review and a summary description of the studies are available as Supplementary material.

The descriptive analysis was conducted first to give a summary of major study characteristics. Of the 417 studies described in the articles analyzed, nearly half (49.6%) were conducted in European countries (see Table 1). Other 136 (32.6%) studies were conducted in North America. The vast majority of the studies (85.7%) were carried out on a sample of adult respondents, with only 60 studies concerned undergraduates/students. Some of the studies measured specific groups of respondents, such as individuals who had not been vaccinated against COVID-19 (e.g., Yang et al., 2021) or health professionals (Al-Sanafi and Sallam, 2021). The majority of the studies (71.2%) had a cross-sectional design, and the remaining studies had an experimental design (23.3%) or a longitudinal design (5.5%).

The objective of the current review was to provide an extensive overview of the empirical studies on CBs within psychology. We present a synthesis of the results of 274 articles published between 2018 and 2021 identified in accordance with the guidelines for systematic reviews. It should be underlined that about half of the respective period coincided with the pandemic period, posing an extraordinary challenge for individuals and institutions, and also resulting in a great number of new conspiracy theories. The current paper presents antecedents as well as consequences of CBs. We grouped the potential antecedents of CBs into six categories: cognitive, motivational, personality, psychopathology, political, and sociocultural factors. Within cognitive psychology, researchers have explored basic cognitive processes, such as illusory pattern perception, and different cognitive biases that can lead to CBs. Growing evidence suggests that analytical thinking is associated with a lower tendency to believe in conspiracies. Within the motivational perspective, relationships were demonstrated between conspiracy thinking and important needs and motives, such as uncertainty avoidance, need for cognitive closure, or need for control. Among individual differences, pathological traits and disorders (such as schizotypy, paranoia, and depression) have gained more attention of conspiracy theory researchers than normal personality traits. The Dark Triad personality traits were also often investigated in the context of CBs.

Among the political antecedents of CBs, researchers analyzed political attitudes and mechanisms of political functioning of individuals. Ideological orientation and party identification were included most often in the research models. Although the research results are not consistent, a clear association can be seen between extremist views and CBs. Analyses of other variables such as anomie, political deprivation and political powerlessness show that poorly perceived political subjectivity predisposes one more strongly to CBs. Although in the analyzed period, relations were sought mainly between CBs and right-wing authoritarianism, it should be emphasized that more recent literature reveals certain paths aimed at analyzing the relations between CBs and left-wing authoritarianism features (Avendaño et al., 2022; Costello et al., 2022). Left-wing authoritarianism predicts higher endorsement of vaccines and support for compulsory vaccination against COVID-19 and penalties for unvaccinated people (Peng, 2022). Galais and Guinjoan (2022) show that people that value security over freedom are more prone to falling for pandemic misbeliefs. CBs are associated with a belief in a hierarchical social order (right-wing) and with anti-hierarchical attitudes about social order (left-wing). In the sociocultural factors group, the researchers looked for links between CBs and cultural values. Relationships between conspiratorial thinking and social media use and the perception of various media content were also confirmed. Research shows that low trust is more strongly associated with conspiratorial thinking. In turn, the associations between religiousness and CBs did not always yield consistent results.

New trends in research into CBs will be identified by comparing the studies covered by this review to the results of the systematic review by Goreis and Voracek (2019), covering studies from 1994 until early 2018. This is made possible by applying identical criteria for selecting the studies covered by these reviews. The one by Goreis and Voracek (2019) included seven papers, also included in this review, since the original and final year of their publication differed. These papers were treated (only for the purpose of comparing the two sets of papers) as components of the set of the systematic review by Goreis and Voracek, and at the same time they were excluded from the set of papers covered by this review to avoid their double attribution.

The comparison between the number of papers included in comparable literature reviews (96 vs. 267, after removing duplicates) shows the dramatic increase in the number of studies published in the years 2018–2021. One of the factors that could be responsible for the increase the interest of researchers in the topic of CBs is the COVID-19 pandemic outbreak that resulted in the emergence of a number of conspiracy theories (related to the origin of the virus, the process of its spread, the consequences or composition of vaccines, etc.) spreading rapidly around the world. The pandemic was a difficult situation, generating many doubts, difficult emotions and, above all, a lack of prospects for many individuals. Thus, this period saw a boom in conspiracy theories providing quick answers to difficult questions. Because of their widespread and universal nature (presence in different cultures), as well as of their easy-to-grasp effect on attitudes and behaviors, it has been easier to conduct comparative studies across cultures, including populations hitherto underrepresented in research of this type. Older research on CBs was conducted mainly on WEIRD (White, Educated, Industrialized, Reach, and Democratic) samples, which hinders the generalization of their results. The number of studies included in both reviews, grouped by publication year, is shown in Figure 2.

In the period covered by the present review, an identical share of cross-sectional studies (71.2%) was recorded compared to the previous period (Goreis and Voracek, 2019; 71,1%). However, the pandemic situation in course encouraged the researchers to perform longitudinal studies (5.5%), not present earlier. The territorial scope of the research was expanded. While the majority of studies continue to be performed in Europe and North America, more studies were recorded in Asia (increase from 4.2 to 6.7%), and some first studies appeared in Africa (nine studies, including multiple continents research). An increase in the number of studies involving more numerous samples was recorded. The number of small studies conducted on fewer than 100 people decreased by far (from 16.3 to 1.7%), while the percentage of research on the most numerous samples of over 500 people increased (from 19.9 to 49.6%). A decrease was recorded in the number of studies on students. In the period covered by our review, 2.5 times fewer studies on students (14.3%) were carried out compared to the previous period in total on the group of graduate and undergraduate students (36.8%). This may have been related to the more difficult access to that group at a time when classes had been suspended in most countries, or were being held online.

The pandemic situation became a source for yet another important trend, namely the increase in the number of practically-oriented studies. In the original review by Goreis and Voracek (2019), few such studies appeared. They concerned, among other things, diagnosing CBs among future teachers with an analysis of the benefits of critical thinking courses as a way of reducing conspiracy beliefs (Ballová Mikušková, 2018) and health-harming behaviors as consequences of CBs (Jolley and Douglas, 2014; Oliver and Wood, 2014). The post-2020 situation saw the emergence of a line of research that involved seeking the factors potentially supporting citizens’ behaviors oriented toward containment of virus spread. In that line of research, CBs constitutes, among other things, a predictor of negative attitudes toward vaccines (e.g., Burke et al., 2021; de Sousa et al., 2021; Eberhardt and Ling, 2021) or boycotting the authorities, or unconventional activity such as participating in demonstrations and protests (e.g., Chayinska and Minescu, 2018; Ardèvol-Abreu et al., 2020).

Goreis and Voracek (2019) pointed out in their systematic review that the majority of research on CBs published until 2018 lacked theoretical background. This conclusion seems to be valid also for the studies included in this review. A similar opinion was expressed by van Prooijen and Douglas (2018, p. 898) in the Introduction to European Journal of Social Psychology Special Issue on conspiracy theories. They stated that “the field is lacking a solid theoretical framework that contextualizes previous findings, that enables novel predictions, and that suggests interventions to reduce the prevalence of conspiracy theories in society.” In the reviewed period, such a theoretical framework, accepted by researchers exploring various themes empirically in the field of research into CBs, does not seem to have appeared. However, over the past few years, a number of papers have been published with the aim of summarizing the current knowledge from the psychological point of view and of outlining the direction of further research (Douglas et al., 2017; Douglas and Sutton, 2018; van Prooijen and Douglas, 2018; van Prooijen and van Vugt, 2018; van Prooijen, 2020; Biddlestone et al., 2021). For example, van Prooijen and Douglas (2018) defined four basic principles of CBs (i.e., the consequential, universal, emotional, and social character of such beliefs), drawn from empirical studies. van Prooijen and van Vugt (2018) proposed an evolutionary model of CBs. van Prooijen (2020) put forward the existential threat model of CBs, asserting that experiencing existential threat triggers epistemic sense-making processes which in turn can lead to CBs only when antagonistic groups are salient. In turn, Biddlestone et al. (2021) presented a model in which CBs are motivated by the frustration of motives associated with three selves (individual, relational, and collective).

Douglas et al. (2017) articulated the need for research on the consequences of CBs. During the period under examination, a significant increase was observed in the number of studies focusing on this topic. However, it is worth noting that most of the studies on potential consequences of CBs had cross-sectional designs and thus causal relationships remained unclear. In the times of the COVID-19 pandemic, when health-related behaviors had an especially high impact on both individual lives and social security and welfare, most of the research on the effects of CBs focused on this particular issue. These studies provided strong evidence that specific COVID-19 beliefs and conspiracy mentality can predict adherence to pandemic measures and a broad range of pandemic-related attitudes and behaviors, including attitudes toward vaccination. Several studies investigated the role of CBs in shaping political behavior. CBs made it possible to predict activity aimed at changing the existing socio-political order for instance through demonstrations or illegal political actions.

The vast majority of research emphasizes the negative individual and social consequences of endorsing CBs. However, positive effects for individuals (such as satisfying their needs) are also potentially possible. van Prooijen (2022) listed the potential psychological benefits connected with a conspiracy worldview as ego-defensive benefits, help in rationalizing the individual’s behavior, and entertainment. Despite the skepticism often expressed by researchers regarding the possibility of satisfying needs as a result of endorsing conspiracy theories, further research is needed to resolve this problem (see: Liekefett et al., 2021).

The analyses were restricted to studies published between 2018 and 2021, which is a relatively short period of time. However, during that time a rapid increase in the number of studies on CBs was observed, which was the motivation for this review. Only published papers retrieved from two databases (Scopus and Web of Science) were used in the review. These indexing databases seem to be the most appropriate considering the theme of the review, and they are widely regarded as high quality sources of scientific articles, but this decision reduces the number of sources taken into account. Thus, it is likely that not all important, relevant studies were included in our review. The rationale behind this decision was that we strived to maintain compliance with the solutions applied by Goreis and Voracek (2019) in their systematic review (see the Current study section). It is also worth noting that our intention was to present the state of knowledge on CBs as widely as possible at this point in time in order to organize and inspire conspiracy theory researchers rather than formulate answers regarding more specific issues (such as prevalence, evaluation of interventions, or measurement issues).

Although validated and reliable measures of CBs were used in many reviewed studies, some of them used very short (1- to 3-item) scales prepared for the particular research, which makes the comparison of the results very difficult. Study publication and outcome reporting biases can affect the results of systematic reviews, especially when meta-analyses were conducted. However, in this study, due to the broadly formulated purpose of the review and the diversity of the reviewed studies, statistical synthesis was not performed. There is also a risk that some errors were made during data extraction. To avoid this, two independent reviewers (using a consensus-based method) were engaged at every stage of preparing the review.

The original contributions presented in this study are included in this article/Supplementary material, further inquiries can be directed to the corresponding author.

IP and AT-K: conception and design and interpretation of the results. IP and PW: systematic literature search. WS-J, AO-M, PW, AT-K, and IP: analysis of the results. IP, AT-K, PW, AO-M, and WS-J: compilation of the results. All authors approved the submitted version for publication.