Background: Family‐related risk and protective factors are crucial for different antisocial behaviors, but their role in radicalization requires synthesis. Radicalization is likely to have a negative impact on families, and well‐designed and implemented family‐focused intervention programs have the potential to decrease radicalization.

Objectives: Research questions were: (1) What are the family‐related risk and protective factors for radicalization? (2) What is the impact of radicalization on families? (3) Are family‐based interventions against radicalization effective?

Search Methods: Searches included 25 databases and hand searches of gray literature from April to July 2021. Leading researchers in the field were asked to provide published and unpublished studies on the topic. Reference lists of the included studies and previously published systematic reviews on risk and protective factors for radicalization were scanned.

Selection Criteria: Published and unpublished quantitative studies on family‐related risk and protective factors for radicalization, the impact of radicalization on families, and family‐focused interventions were eligible with no restrictions regarding the study year, location, or any demographic characteristic. Studies were included if they measured the relation between a family‐related factor and radicalization or if they included a family‐focused intervention against radicalization. For family‐related risk and protective factors, radicalized individuals needed to be compared to general population. Studies were included if they defined radicalization as support or commission of violence to defend a cause, including support for radical groups.

Data Collection and Analysis: The systematic search identified 86,591 studies. After screening, 33 studies focused on family‐related risk and protective factors were included, with 89 primary effect sizes and 48 variables grouped in 14 factors. For the factors that included two or more studies, meta‐analyses with random effects were conducted. When possible, moderator analyses were performed together with sensitivity and publication bias analyses. No studies on the impact of radicalization on families or family‐focused interventions were included.

This meta-analysis summarizes evidence on families and radicalization. It could not locate any studies on the consequences of radicalization for families or family-focused interventions that met its inclusion and exclusion criteria (requiring quantitative studies). The review showed that "parental ethnic socialization, extremist family members and family conflict were significant risk factors for radicalization whereas high family socioeconomic status, bigger family size, and high family commitment were significant protective factors against radicalization." The review found that family violence was related to more radicalization in Western countries, and more related to radicalization in adolescents, and more related to cognitive radicalization (as opposed to behavioral radicalization).

The study found some evidence that the following interventions may be effective: 1) decreasing bias against other cultures and ethnicities, teaching about different cultures and teaching that people are all equal would be desirable; 2) countering extremism in families, not only individuals; 3) promotion of family commitment; 4) increasing levels of education and social wellbeing to reduce exclusion of less affluent individuals and families.