Information Sources and Database Search

A literature search of all studies on sibling conflicts was conducted. The time frame of the first search was from 1970 until February 2015. The commencement date was 1970 because research on sibling relationships began to thrive in the 1970s, after Bowlby’s Attachment Theory (1973) and Bronfenbrenner’s Ecological Systems Model

(1979) (Milevsky, 2011). The following data bases were used to carry out the search: PsychInfo, PubMed, Social Sciences Full Text, Scopus, ERIC, Web of Science, MEDLINE and Education Research Complete. The data bases were chosen because they cover a range of related and relevant disciplines: psychology, sociology, education and other associated multidisciplinary topics. The selection of search terms was

relatively broad, in order to maximise the potential to obtain wide-ranging and comprehensive indicators of the factors associated with sibling conflicts. The broad nature of the search is demonstrated by the respective search terms that were utilised; bully*, bulli*, victim*, violen*, harass*, aggress*, fight*, antisocial, delinquen* (* represents that the search includes the respective words and all possible fragments). These terms were inserted with the Boolean operator ‘OR’ in conjunction with sibling*, sister* and brother*. Scopus was directed to search for the relevant terms in the ‘title’, ‘abstract’ and ‘key terms’; PubMed was directed to search in ‘title’ and ‘abstract’; and

Web of Science was directed to search in ‘topic’. For the databases ERIC, PsychInfo, MEDLINE, Education Research Complete and Social Science Full Text it was only

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possible to select either ‘title’ or ‘abstract, in which cases, the ‘abstract’ option was

selected. After the search, articles were then sorted based on the previously set

exclusion and inclusion criteria (see below). The studies that were included were then further grouped based on the respective variables each study examined. The results of this coding process made it apparent that the meta-analysis could be further improved by narrowing its focus. Based on the groups that had emerged from the coding, the factors associated with sibling conflicts were subdivided into four core areas: SES, Domestic Violence, Parental Mental Health and Parenting Practices. The first stage of a meta-analysis was then re-visited.

The time frame of the second search was from 1970-February 2016. The same search engines were utilised: PsychInfo, PubMed, Social Sciences Full Text, Scopus, ERIC, Web of Science, MEDLINE and Education Research Complete. New search terms were determined based on outcomes from the first search and other meta- analyses in related research areas (Kitzmann, Gaylord, Holt & Kenny, 2003; Lorant, Eaton, Robert, Philippot & Ansseau, 2003; Sirin, 2005; Davies, Evans & DiLillo, 2008; Reijntjes, Kamphuis, Prinzie & Telch, 2010; Lereya, Samara & Wolke, 2013). For each subgroup (SES, Domestic Violence, Parental Mental Health and Parenting Practices) the relevant search terms were entered in the search engines, in conjunction with ‘sibling* OR sister* OR brother*’ (Figure 2.1). As the literature on parenting practices

is enormous, it was necessary to narrow this search further. This was done to maximise the chances that the search results would exclusively be related to the relationship between parenting practices and sibling conflicts. Therefore, the search terms for ‘Parenting Practices’ was additionally inserted in conjunction with ‘AND bully* OR

bulli* OR victim* OR viole* OR aggress* OR harass* OR fight* OR antisocial* OR delinquen*’. Additionally, manual searches were conducted by scanning reference lists

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2.2.1.1. Eligibility Criteria and Study Selection

Inclusion criteria. For an article to be included in the analysis (Table 2.1), first

it had to adopt a quantitative methodology. Second, studies on direct and/or indirect sibling conflicts were included, where direct conflicts referred to a sibling directly physically and/or verbally harming another sibling, and indirect conflicts referred to a sibling purposefully manipulating the social dynamics within a family, excluding and telling on a sibling to a parent (Wolke & Samara, 2004). Studies that referred to sibling conflicts with a distinct term, such as relational aggression were also included, due to cross-cultural differences in terminology. Third, the measures of sibling relationships should have been conducted through self-report measures (by the child and his/her sibling), parental reports of sibling relationship, and/or observational studies. The same principles were employed for the proximal and distal factors (e.g. SES, domestic violence, parental mental health and parenting). The inclusion analysis was not limited to sibling dyad relationships only; it was also possible to have a target child (TC) reporting about the sibling relationship with one or more siblings overall. Fourth, the study had to contain (or the authors needed to provide upon request) sufficient statistical information to be able to calculate an effect size (correlations, means, and standard deviations, odds ratio and standard errors, event rates and sample size). Fifth, the mean ages of TCs had to be below 18 years. Sixth, published and unpublished articles were included for analysis. Lastly, articles in English and Spanish were included.

Exclusion criteria. Qualitative, retrospective and intervention studies were

excluded (Table 2.1). Retrospective studies were excluded as they tend to have low validity and high response bias, as participants may tend to confabulate their memory, due to the retrospective nature (Briere, 1992). Studies that only looked at samples from clinical populations were excluded. Further, exclusions were made for studies that only

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had twin, adoptive and foster populations in their experimental conditions. Finally, meta-analyses were also excluded, although their reference lists were scanned to avoid omitting relevant studies.

Table 2.1. Inclusion and Exclusion Criteria

Inclusion Criteria Exclusion Criteria

Study Design - Quantitative Studies - Cross-Sectional - Longitudinal - Qualitative Studies - Retrospective Studies - Intervention Studies - Meta-Analyses Sample

- Children and siblings mean age had to be below the age of 18 years

- Only typically developing children

- Samples of solely clinical populations - Exclusively twin

samples

- Exclusively adoptive and/or foster samples Measures of

Outcome Variables

- Self-report measures of sibling relationships (child and/or siblings) - Only TCs reporting about the sibling

relationship

- Direct and/or indirect conflict between siblings

Reporting of Outcome Variables

- Reports of quality of relationship between sibling dyads

- Reports of quality of relationship between one or more siblings overall

Measures of Predictor Variables

- Child- or parent- self-report measures of any of the possible precursors that fall in the previously set categories (parental mental health, domestic violence, SES and parenting practices)

- Authors’ observational reports of any of the possible precursors that fall in the previously set categories (parental mental health, domestic violence, SES and parenting practices)

Terminology - Studies that referred to conflicts with a distinct term, such as relational

aggression

Analysis

- Sufficient statistical information in order to be able to calculate an effect size (correlations, means, and standard deviations, odds ratio, t values, chi- squares) (either present in article, or provided by authors upon request Status of Article - Published and unpublished articles (e.g.

doctor theses)

Language - Articles did not have to be exclusively in English

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