Better evidence for a better world
Better evidence for a better world

Better evidence for a better world (173)

Additional Info

  • Published date 2019-06-01
  • Title Other evidence and gap maps (EGMs)

Additional Info

  • Authors Ruth Pitt
  • Published date 2018-08-22
  • Coordinating group(s) Crime and Justice
  • Type of document Policy brief
  • Title Policy brief 5: Effectiveness of focused policing strategies
  • Library Image Library Image
  • English

    This Campbell policy brief summarises findings from systematic reviews on focused policing strategies, the consequences of geographically-focused policing for neighbouring areas, and community perceptions of police legitimacy.

Additional Info

  • Authors Heather Menzies Munthe-Kaas, Rigmor C Berg, Nora Blaasvær
  • Published date 2018-02-28
  • Coordinating group(s) Social Welfare
  • Type of document Review Plain language summary
  • Title Effectiveness of interventions to reduce homelessness
  • Library Image Library Image
  • See the full review https://onlinelibrary.wiley.com/doi/10.4073/csr.2018.3
  • Records available in English, Spanish
  • English

    PLAIN LANGUAGE SUMMARY

    Interventions to reduce homelessness and improve housing stability are effective

    There are large numbers of homeless people around the world. Interventions to address homelessness seem to be effective, though better quality evidence is required.

    What did the review study?

    There are large numbers of homeless people around the world. Efforts to combat homelessness have been made on national levels as well as at local government levels.

    This review assesses the effectiveness of interventions combining housing programmes with or without case management as a means to reduce homelessness and increase residential stability for individuals who are homeless, or at risk of becoming homeless.

    What is the aim of this review?

    This Campbell systematic review examines the effectiveness of interventions to reduce homelessness and increase residential stability for individuals who are homeless, or at risk of becoming homeless. Forty-three studies were included in the review, 37 of which are from the USA.

    What studies are included?

    Included studies were randomized controlled trials of interventions for individuals who were already, or at-risk of becoming, homeless, and which measured impact on homelessness or housing stability with follow-up of at least one year.

    A total of 43 studies were included. The majority of the studies (37) were conducted in the United States, with three from the United Kingdom and one each from Australia, Canada, and Denmark.

    What are the main results in this review?

    Included interventions perform better than the usual services at reducing homelessness or improving housing stability in all comparisons.

    These interventions are:

    • High- and low-intensity case management
    • Housing First
    • Critical time intervention
    • Abstinence-contingent housing
    • Non-abstinence-contingent housing with high-intensity case management
    • Housing vouchers
    • Residential treatment

    These interventions seem to have similar beneficial effects, so it is unclear which of these is best with respect to reducing homelessness and increasing housing stability. Evidence with moderate certainty is available for high-intensity case management and housing first compared to usual services.

    What do the findings in this review mean?

    A range of housing programs and case management interventions appear to reduce homelessness and improve housing stability, compared to usual services.

    However, there is uncertainty in this finding as most the studies have risk of bias due to poor reporting, lack of blinding, or poor randomization or allocation concealment of participants. In addition to the general need for better conducted and reported studies, there are specific gaps in the research with respect to: 1) disadvantaged youth; 2) abstinence-contingent housing with case management or day treatment; 3) non-abstinence contingent housing comparing group vs independent living; 4) Housing First compared to interventions other than usual services, and; 5) studies outside of the USA.

    How up-to-date is this review?

    The review authors searched for studies published up to January 2016.

  • Spanish

    Click on 'Download PDF' on the right to view the plain language summary in Spanish.

Additional Info

  • Authors Giel Ton, Sam Desiere, Wytse Vellema, Sophia Weituschat, Marijke D'Haese
  • Published date 2017-12-12
  • Coordinating group(s) International Development
  • Type of document Review Plain language summary
  • Title The effectiveness of contract farming for raising income of smallholder farmers in low- and middle-income countries
  • Library Image Library Image
  • See the full review https://onlinelibrary.wiley.com/doi/10.4073/csr.2017.13
  • Records available in English, Spanish
  • English

    PLAIN LANGUAGE SUMMARY

    Contract farming improves incomes for better-off farmers

    Contract farming, a sales arrangement between a farmer and a firm, is popular with government and donors. Contract farming can produce substantial income gains for farmers. Moreover, these benefits may well be required for contract farming schemes to survive. Better- off farmers are most likely to participate in contract farming schemes.

    What did the review study?

    Contract farming is a sales arrangement agreed before production begins, which provides the farmer with resources or services. The service package provided by the firm varies per location, and can include transport, certification, input provisioning and credit.

    This systematic review summarises evidence on income effects for smallholders to assess average effects and explore combinations of factors that increase these effects.

    What is the aim of this review?

    This Campbell systematic review examines the impact of contract farming on income and food security of smallholder farmers in low- and middle-income countries. The review summarises findings from 75 reports, of which 22 (covering 26 contract farming interventions) were used for meta-analysis.

    What studies are included?

    Included studies had to examine the impact of contract farming on income and food security of smallholder farmers in low- and middle-income countries. Studies had to use a comparison group with appropriate statistical methods to allow for selection effects.

    Seventy-five studies were identified with quantitative estimates of the impact of contract farming of which 22 studies, covering 7,471 respondents, were of sufficient rigour to include in the meta-analysis of income effects. The meta-analysis covers 26 empirical instances of contract farming in 13 developing countries.

    What are the main results in this review?

    Contract farming may substantially increase farmer income with an average effect in the range of 23 to 54 per cent. There is upward bias in the estimate because of survivor bias in individual studies (no data on farmers who drop out of schemes) and in the body of evidence (no studies on contract farming arrangements that collapsed in their initial years), and publication bias in the literature (under-reporting of insignificant outcomes). Therefore, some caution is needed in interpreting the findings.

    For farmers to give up their autonomy in marketing and prevent side-selling, substantial income gains need to be offered. This is especially so for annual crops and when firms have contracts directly with farmers rather than through a cooperative.

    Poorer farmers are not usually part of contract farming schemes. In 61% of the cases, contract farmers had significantly larger landholdings or more assets than the average farmers in the region.

    What do the findings in this review mean?

    Contract farming covers a wide range of contractual arrangements. This heterogeneity makes it difficult to draw general conclusions from the literature published on this topic. The lack of studies on ‘failed treatments’ leads to an overestimation of the effectiveness of contract farming.

    Moreover, the analysis suggests a marked publication bias; all studies report on at least one case of contract farming that has a positive and statistical significant income effect.

    Relatively larger or richer farmers can cope better with these risks and are, therefore, more likely to take part in a contractual arrangement. This implies that contract farming is more suited to the relatively better-off segment of the farming population.

    Further research should: (1) improve reporting of the intervention; (2) document the less-successful instances of contract farming, and report inconclusive results (insignificant effects); and (3) capture other outcomes of contract farming such as (sector-wide) innovation, and livelihood resilience.

    How up-to-date is this review?

    The review authors searched for studies published up to October 2015.

  • Spanish

    Click on 'Download PDF' on the right to view the plain language summary in Spanish.

Additional Info

  • Authors Hugh Waddington, Ada Sonnenfeld, Juliette Finetti, Marie Gaarder, Denny John, Jennifer Stevenson
  • Published date 2019-08-02
  • Coordinating group(s) International Development
  • Type of document Review Plain language summary
  • Title Citizen engagement in public services in low‐ and middle‐income countries: A mixed‐methods systematic review of participation, inclusion, transparency and accountability initiatives
  • Library Image Library Image
  • See the full review https://onlinelibrary.wiley.com/doi/full/10.1002/cl2.1025
  • English

    PLAIN LANGUAGE SUMMARY

    Citizen engagement improves access to public services in low- and middle-income countries, but evidence on development outcomes is limited

    Interventions promoting citizen engagement in public service management involve participation, inclusion, transparency and accountability (PITA) mechanisms. In low- and middle-income countries (LMICs), these interventions are effective in improving active citizenship and service delivery, and may improve the responsiveness of service provider staff for services provided directly by public servants (for example, in health).

    In contrast, interventions providing information to stimulate pressure on politicians are not usually effective in improving provider response or service delivery. There is insufficient evidence to conclude whether these interventions are effective in improving wellbeing or the relationship between citizens and the state.

    What is this review about?

    Failures in governance lead to the exclusion of large portions of society from public services and to waste, fraud and corruption. This review assesses evidence for interventions promoting better governance of public services: participation (participatory planning), inclusion (involvement of marginalised groups), transparency (information about citizen rights or performance of public officials), and accountability (citizen feedback) mechanisms, known collectively as PITA mechanisms.

    What is the aim of this review?

    This Campbell systematic review examines the effects of interventions to promote citizen engagement in public service management. The review synthesises evidence from 35 impact evaluations and 36 related studies of interventions promoting participation, inclusion, transparency and accountability (PITA) mechanisms.

    What studies are included?

    The review includes impact evaluations relating to 35 PITA programmes from 20 LMICs. In addition, 36 qualitative and programmatic documents were included to strengthen understanding of implementation context and programme mechanisms.

    What are the main findings of this review?

    Citizen engagement interventions (i) are usually effective in improving intermediate user engagement outcomes, for example, meeting attendance and contributions to community funds; (ii) improve access to and quality of services but not service use outcomes; (iii) can lead to improvements in some wellbeing outcomes such as health and productive outcomes; (iv) may improve tax collection; but (v) do not usually lead to changes in provider action outcomes such as public spending, staff motivation and corruption. There may be an exception where there is direct interaction between citizens and service providers in the regular delivery of services. Interventions providing performance information do not generally improve access or lead to improvements in service quality.

    Only interventions focused on services delivered by front-line staff (e.g., in health) achieve positive outcomes. Those delivered without public interaction (e.g., roads) do not. However, engagement with civil society organisations and interest groups may lead to better outcomes for services accessed independently of providers. Inclusive citizen engagement programmes have at least as big an effect on user engagement and access to services as less inclusive approaches.

    Many interventions experienced challenges stemming from a lack of positive engagement with supply-side actors, whose power the interventions often sought to diminish. Interventions implemented with the strong support of the targeted service providers were better able to realise positive impacts.

    Approaches to citizen-service provider engagement appear to work more effectively when implemented through phased, facilitated collaborative processes rather than one-off accountability meetings that are seen as confrontational.

    Only four studies present any data on intervention costs. This limited the potential for any analysis of comparisons across programmes and settings.

    In interpreting the findings, it must be noted that each individual outcome is reported in only a few studies and that included studies have important methodological weaknesses with risks of bias arising from weak design, analysis and reporting.

    What do the findings of this review mean?

    For policy and programme managers: A collaborative rather than confrontational approach with the service providers whose services are under scrutiny is more likely to be effective. Engaging communities may require using civil society organisations to facilitate the community’s participation. Programme design should ensure positive engagement with supply-side actors within the intervention setting.

    For researchers: More high-quality studies are needed, comparing different approaches to improving service delivery, paying attention to complete description of the different approaches being compared. Since implementation is a crucial factor, mixed methods studies should be the norm, and will help focus on equity considerations which have been neglected. Finally, there should be standardisation of indicators in PITA studies.

    How up-to-date is this review?

    The review authors searched for studies up to March 2018.

Additional Info

  • Authors Birte Snilstveit, Jennifer Stevenson, Laurenz Langer, Natalie Tannous, Zafeer Ravat, Promise Nduku, Joshua Polanin, Ian Shemilt, John Eyers, Paul J Ferraro
  • Published date 2019-09-29
  • Coordinating group(s) International Development
  • Type of document Review Plain language summary
  • Title Incentives for climate mitigation in the land use sector: a mixed-methods systematic review of the effectiveness of payment for environment services (PES) on environmental and socio-economic outcomes in low- and middle-income countries
  • Library Image Library Image
  • See the full review https://onlinelibrary.wiley.com/doi/full/10.1002/cl2.1045
  • English

    PLAIN LANGUAGE SUMMARY

    Payment for environmental services (PES) remains high-risk strategy for climate change mitigation until rigorous impact evaluations can determine its effects

    Programmes that provide economic incentives to reduce the negative environmental impact of land use are a popular means to reduce deforestation and degradation and mitigate climate change. In some cases they also aim to improve socio-economic outcomes. The effects of Payment for environmental services (PES) programmes on these outcomes, however, remain unclear due to the low quality of available evidence.

    What is this review about?

    Greenhouse gas is released by unsustainable practices in the land use sector. PES programmes seek to create positive environmental outcomes by providing an economic incentive to the owners and managers of environmental services in low- and middle-income countries to change their behaviour.

    This review uses existing evidence to assess whether PES programmes have positive effects on environmental and socio-economic outcomes. It also assesses how these effects vary across different contexts and implementation strategies.

    What is the aim of this review?

    This Campbell systematic review examines the effects of Payment for Environmental Services (PES) programmes on environmental and socio-economic outcomes in low- and middle-income countries. The review summarises findings from 44 quantitative and 60 qualitative studies from 12 countries.

    What studies are included?

    Studies were included that evaluated a PES programme in low- and middle-income countries and targeted populations living in or near forests, agricultural land, wetlands, grasslands and mangroves.

    Forty-four impact evaluations and 60 qualitative studies were included. They covered 18 programmes from 12 countries in Latin America and the Caribbean, East Asia and Pacific, South Asia and sub-Saharan Africa.

    Ten of the 18 programmes had as their objectives the improvement of both environmental and socio-economic outcomes.

    What are the main findings of this review?

    PES may produce reduced deforestation, improved forest cover and increased household income. These findings are, however, based on low and very low quality evidence from a small number of countries, and should be treated with caution.

    Qualitative data indicates that the effects will vary, depending on where and to whom projects are targeted, the quality of implementation, presence of governance structures, contextual factors, and attitudes towards environmental protection and towards PES itself.

    What do the findings of the review mean?

    Until higher quality research is conducted, the large-scale implementation of PES programmes should be considered a high-risk strategy for mitigating climate change.

    Based on the current evidence, strong conclusions about the impact of PES cannot be made, however effective targeting and including strong governance structures may improve project results.

    To address the evidence gap, funders and implementing agencies should collaborate to develop rigorous methods for impact evaluation. They should also invest in the collection and analysis of qualitative data that examines diverse research participants and follows change over longer periods.

    How up-to-date is this review?

    The review authors searched for studies in August and September 2017.

Additional Info

  • Authors Maren Duvendack, Philip Mader
  • Published date 2019-01-07
  • Coordinating group(s) International Development, Methods
  • Type of document Review Plain language summary
  • Title Impact of financial inclusion in low‐ and middle‐income countries: A systematic review of reviews
  • Library Image Library Image
  • See the full review https://onlinelibrary.wiley.com/doi/10.4073/csr.2019.2
  • Records available in English, Hindi, Spanish
  • English

    PLAIN LANGUAGE SUMMARY

    Financial inclusion interventions have very small and inconsistent impacts

    A wide range of financial inclusion programmes seek to increase poor people’s access to financial services to enhance the welfare of poor and low-income households in low- and middle-income countries. The impacts of financial inclusion interventions are small and variable. Although some services have some positive effects for some people, overall financial inclusion may be no better than comparable alternatives, such as graduation or livelihoods interventions.

    What is this review about?

    Financial inclusion programmes seek to increase access to financial services such as credit, savings, insurance and money transfers and so allow poor and low-income households in low- and middle-income countries to enhance their welfare, grasp opportunities, mitigate shocks, and ultimately escape poverty.  This systematic review of reviews assesses the evidence on economic, social, behavioural and gender-related outcomes from financial inclusion.

    What is the aim of this review?

    This systematic review of reviews systematically collects and appraises all of the existing meta-studies – that is systematic reviews and meta-analyses – of the impact of financial inclusion. The authors first analyse the strength of the methods used in those meta-studies, then synthesise the findings from those that are of a sufficient quality, and finally, report the implications for policy, programming, practice and further research arising from the evidence. Eleven studies are included in the analysis.

    What are the main findings of this review?

    What studies are included?

    This review includes studies that synthesise the findings of other studies (meta-studies) regarding the impacts of a range of financial inclusion interventions on economic, social, gender and behavioural outcomes. A total of 32 such meta-studies were identified, of which 11 were of sufficient methodological quality to be included in the final analysis. The review examined meta-studies from 2010 onwards that spanned the globe in terms of geographical coverage.

    Impacts are more likely to be positive than negative, but the effects vary, are often mixed, and appear not to be transformative in scope or scale, as they largely occur in the early stages of the causal chain of effects. Overall, the effects of financial services on core economic poverty indicators such as incomes, assets or spending, and on health status and other social outcomes, are small and inconsistent. Moreover, there is no evidence for meaningful behaviour-change outcomes leading to further positive effects.

    The effects of financial services on women’s empowerment appear to be generally positive, but they depend upon programme features which are often only peripheral or unrelated to the financial service itself (such as education about rights), cultural and geographical context, and what aspects of empowerment are considered.

    Accessing savings opportunities appears to have small but much more consistently positive effects for poor people, and bears fewer downside risks for clients than credit. A large number of the meta-studies included in the final analysis voiced concerns about the low quality of the primary evidence base that formed the basis of their syntheses. This raises concerns about the reliability of the overall findings of meta-studies.

    What do the findings of this review mean?

    This systematic review of reviews draws on the largest-ever evidence base on financial inclusion impacts.  The weak effects found warn against unrealistic hype for financial inclusion, as previously happened for microcredit. There are substantial evidence gaps, notably studies of sufficient duration to measure higher-level impacts which take time to materialize, and for specific outcomes such as debt levels or indebtedness patterns and the link to macroeconomic development.

    This study is the first review of reviews published by the Campbell Collaboration. Some important limitations were encountered working at this level of systematisation.  It is recommended that authors of primary studies and meta-studies engage more critically with study quality and ensure better, more detailed reporting of their concepts, data and methods. More methods guidance and clearer reporting standards for the social science and international development context would be helpful.

    How up-to-date is this review?

    The review authors searched for studies in November 2017, updating elements of the searches in January 2018. This Campbell Systematic Review was published in January 2019.

  • Spanish

    Click on 'Download PDF' on the right to view the plain language summary in Spanish.

  • Hindi

    Click on 'Download PDF' on the right to view the plain language summary in Hindi.

Additional Info

Additional Info

  • Authors Rehana Salam, Simon Cousens, Vivian Welch, Michelle Gaffey, Philippa Middleton, Maria Makrides, Paul Arora, Zulfiqar Bhutta
  • Published date 2019-09-24
  • Coordinating group(s) International Development
  • Type of document Review Plain language summary
  • Title Mass deworming for soil‐transmitted helminths and schistosomiasis among pregnant women: A systematic review and individual participant data meta‐analysis
  • Library Image Library Image
  • See the full review https://onlinelibrary.wiley.com/doi/10.1002/cl2.1052
  • English

    PLAIN LANGUAGE SUMMARY

    Mass deworming during pregnancy reduces anaemia but has no effect on other maternal or pregnancy outcomes

    Pregnant women are at particular risk from soil transmitted helminthiasis (STH) – a group of diseases caused by infection with four intestinal parasites and schistosomiasis. Individual-level data analysis with data from three studies shows that mass deworming during pregnancy reduces anaemia but has no effect on any other maternal or pregnancy outcomes.

    What is this review about?

    Soil transmitted helminthiasis (STH) are a group of diseases caused by infection with four intestinal parasites (two types of hookworm, roundworm, and whip worm) which contributed to a total of 4.98 million years lived with disability (YLDs) in 2010. Anaemia is one of the most common side effects of infection with STH or schistosomes, due to blood loss in the intestine or urinary tract. Women in low- and middle-income countries (LMICs) are especially prone since they may be pregnant or lactating for as much as half of their reproductive lives, with over 50% of the pregnant women having iron-deficiency anaemia.

    This review explores whether the effect of mass deworming during pregnancy varies with individual characteristics (nutritional status, anaemia), intensity of infection (as assessed by egg count), infection status (including species of worm), socioeconomic status, sanitation environment and co-interventions. The analysis uses individual patient data (IPD), which means that the original individual-level data are obtained for the included studies and combined into a single data set.

    What is the aim of this review?

    This Campbell systematic review explores whether the effect of mass deworming during pregnancy varies with individual characteristics, intensity of infection, infection status, socioeconomic status, sanitation environment and co-interventions.

    What studies are included?

    Included studies have to be individually randomised controlled trials: cluster randomised controlled trials and quasi randomised studies providing preventive or therapeutic deworming drugs for STH and schistosomiasis during pregnancy.

    From a total of 16 studies on mass deworming during pregnancy, we identified seven trials with 8,515 participants which were eligible for individual data analysis. Of these seven trials, we received data from three trials so that data was captured for 5,957 participants.

    What are the main findings of this review?

    Mass deworming during pregnancy reduces maternal anaemia by nearly one quarter (23%).

    There is no effect of mass deworming during pregnancy on any other outcomes including Trichiura infection, hookworm infection, low birth weight, and pre-term birth.

    The size of the effect is not affected by Trichiura intensity at baseline, maternal anemia at baseline and maternal BMI at baseline. However these findings should be interpreted with caution due to small sample sizes. Other potential moderating characteristics could not be assessed because of lack of data.

    The quality of evidence for our findings is rated as moderate. Further research on maternal baseline worm intensities and birth outcomes could change our findings.

    What do the findings of the review mean?

    The analyses suggest that mass deworming during pregnancy is associated with reducing anaemia, with no effect on any other maternal or pregnancy outcomes.

    The analyses were limited by the availability of data for the impact by sub-groups and effect modification. Thus, there is a need to assess mass deworming for STH and schistosomiasis during pregnancy in large-scale programmatic settings, along with an attempt to measure various individual and environmental factors that could potentially affect its impact.

    There is also a need to support and promote open data for future individual level data analysis.

    How up-to-date is this review?

    The review authors searched for studies up to March 2018.

Additional Info

  • Authors Dan Fitzpatrick, Jason Burns
  • Published date 2019-09-24
  • Coordinating group(s) Education
  • Type of document Review Plain language summary
  • Title Single-track year-round education for improving academic achievement in US K-12 schools
  • Library Image Library Image
  • See the full review https://onlinelibrary.wiley.com/doi/10.1002/cl2.1053
  • English

    PLAIN LANGUAGE SUMMARY

    Single-track year-round education modestly improves average math and reading achievement of K-12 students

    Single-track year-round education (YRE) is linked to higher average achievement in both math and reading, though not overall student proficiency rates. Achievement gains are similar in magnitude to the degree of summer learning loss documented in other studies.

    What is this review about?

    Over the long summer break, students forget some of what they learned during the school year. This “summer learning loss” is especially large for low-income students. One policy aimed at decreasing summer learning loss is year-round education (YRE): re-distributing the usual number of school days so that students have more short breaks during the school year, and a much shorter summer vacation.

    A specific design used to achieve this goal is single-track YRE, which involves placing all students at a given school on the same year-round calendar.

    This review considers evidence on the effect of single-track YRE on academic achievement – test scores and proficiency rates – of K-12 students in math and reading from studies published between 2001 and 2016.

    What is the aim of this review?

    This Campbell systematic review synthesizes the findings from 30 studies that compared the performance of students at schools using single-track year-round calendars to the performance of students at schools using a traditional calendar.

    What studies are included?

    This review includes studies that compare achievement in single-track YRE schools to achievement in traditional-calendar schools. Of a total of 39 studies on the topic, nine reported outcomes in a way that could not be combined with the 30 that this review focuses on. The studies were from 2001-2016 and were all of K-12 schooling in the USA, but varied in school characteristics (state, size, percent minority, percent low-income).

    None of the studies used an experimental design (random assignment); studies were about evenly split between (a) comparing one school to another that is very similar, (b) comparing one school to a nearby school, and (c) comparing students at a school before versus after a switch to a year-round calendar.

    What are the findings of this review?

    Is academic achievement higher at YRE schools?

    Average student achievement was higher in both reading and math at single-track YRE schools, but proficiency rates were no higher in either subject. Compared to a prior meta-analysis of summer learning loss, which found that students typically forget the equivalent of one month’s learning over the summer, this review found the gain from YRE to be slightly more than this in reading and slightly less in math.

    Do some students benefit more from YRE?

    For the most part, no. Low-income and minority students do not see greater benefit from YRE than average students in either reading or math. Elementary and middle school students show about the same gain in reading. However, we find that middle school students’ achievement in math increases more than elementary school students’ from the year-round calendar.

    Do some year-round calendars help students more than others?

    Tentatively, yes: the schools that shortened summers to the fewest weeks had the largest effect on student achievement in both math and reading.

    What do the findings of the review mean?

    Single-track YRE appears to have a benefit to student achievement that is similar in magnitude to the learning loss students experience over the traditional 10-week summer break.

    YRE does not appear to be more helpful for low-income or minority students than for the average student, but might have a larger effect for middle school students than elementary school students in math.

    Schools that shortened summer to the fewest weeks of vacation showed the greatest gain in student achievement. This seems to indicate that most schools can expect an improved student achievement gain from a year-round calendar, equivalent to one month of learning, with a larger improvement from shortening the summer break to 4-6 weeks than from shortening the summer break to 7-8 weeks.

    How up-to-date is this review?

    The review authors searched for studies up to 2016, with electronic searches conducted in July and August 2017.

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