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Replication is an important tool to promote high quality research and ensure policy makers can rely on studies in making guidelines or funding programs. By ensuring influential studies are replicable we provide assurance that the policies based on these studies are well-founded and the conclusions and recommendations are robust-to different estimation models or different choices. In this paper, we argue that replication is not only useful but necessary to ensure that an author's choice in how to analyse data is not the only factor that determines whether an intervention is effective or not. We also show that while most research is done well and provides robust results, small differences can lead to different interpretations and these differences need to be acknowledged. This special issue highlights 5 such replication studies, which are replications of influential studies on biomedical, social, behavioural and structural interventions for HIV prevention and treatment. We reflect on their findings. Four out of five studies, which conduct push button replication and pure replication, were able to reproduce the results of the original studies with minor differences, mainly due to minor typographical errors or rounding differences. The analysis of the measurement and estimation analyses conducted in these five studies reveals that the original results are not very robust to alternative analytical approaches, especially when these results rely on a small number of observations. In these cases, the original results are weakened. Furthermore, in contrast to the original papers, two of the five included replication studies conducted a theory of change analysis-to explore how or why the interventions work (or do not) not just whether the intervention works or not. These two analyses indicate that the estimated impacts of the interventions are drawn from few mediators. In addition, they demonstrate that, in some cases, a lack of effect may be related to lack of adequate exposure to the intervention rather than inefficacy of the intervention per se. However, overall, the included replication studies show that the results presented in the original papers are trustworthy and robust, especially when based on larger sample sizes. Replication studies can not only verify the results of a study, they can also provide additional insights on the published results, such as how and why an intervention was effective or less effective than expected. They can thus be a tool to inform the research community and/ or policymakers about whether and how interventions could be adopted, which need to be tested further, and which should be discontinued because of their ineffectiveness. Thus, publishing these replication studies in peer-reviewed journals makes the work public and publicized. The work advances knowledge, and publication should be encouraged, as it is for other types of research.

Co-diagnosis of HIV and tuberculosis presents a treatment dilemma. Starting both treatments at the same time can cause a flood of immune response called immune reconstitution inflammatory syndrome (IRIS) which can be lethal. But, how long to delay HIV treatment is less understood. In 2011, based on the conclusions of three separate studies, WHO recommended starting HIV treatment earlier for those with later HIV disease progression. This paper conducts a replication study of one of the three studies, by Havlir and colleagues. Using their publicly available data, we were able to replicate most of the results presented in the original paper. In our measurement and estimation analyses we use different estimation techniques to assess the robustness of the results. We find that adjusting for loss to follow-up does not affect the main results of the paper. However, an ANCOVA estimation and an instrumental variable model weaken the main result of the paper of better outcomes with early HIV treatment only for those who are sicker, reducing significance from the 5% to the 10% level. A change-point analysis also detects no changes in effect by timing of HIV treatment initiation or different thresholds of CD4 count for the primary outcome. This result suggests that the choice of start time for HIV treatment initiation should be based on other factors including potential drug interactions, overlapping side effects, a high pill burden and severity of illness rather than CD4 threshold and preset timeframes. While we caution against overgeneralizing, the result of this replication is aligned with more recent studies that show no evidence that early initiation of HIV treatment reduces mortality for any patients.

Rigorous and transparent bias assessment is a core component of high-quality systematic reviews. We assess modifications to existing risk of bias approaches to incorporate rigorous quasi-experimental approaches with selection on unobservables. These are nonrandomized studies using design-based approaches to control for unobservable sources of confounding such as difference studies, instrumental variables, interrupted time series, natural experiments, and regression-discontinuity designs. We review existing risk of bias tools. Drawing on these tools, we present domains of bias and suggest directions for evaluation questions. The review suggests that existing risk of bias tools provide, to different degrees, incomplete transparent criteria to assess the validity of these designs. The paper then presents an approach to evaluating the internal validity of quasi-experiments with selection on unobservables. We conclude that tools for nonrandomized studies of interventions need to be further developed to incorporate evaluation questions for quasi-experiments with selection on unobservables.

Although HIV self-testing may overcome some barriers to HIV testing, various stakeholders have expressed concerns that HIV self-testing may lead to unintended harm, including psychological, social and medical harm. Recognizing that similar concerns were raised in the past for some other self-tests, we conduct a review of the literature on a set of self-tests that share some characteristics with HIV self-tests to determine whether there is any evidence of harm. We find that although the potential for harm is discussed in the literature on self-tests, there is very little evidence that such harm occurs.

To identify determinants of egg consumption in infants and young children aged 6-23·9 months in Ethiopia. Data used were from the cross-sectional baseline survey of an egg campaign in Ethiopia implemented by the Global Alliance for Improved Nutrition. Children aged 6-23·9 months ( 453) were sampled. Data on socio-demographic characteristics, economic resources, caregiver's behaviour, child health and feeding practices, and egg consumption in the last 7 d were collected using interviewer-administered questionnaires. Multivariable ordinal logistic regression was used to examine the association between explanatory variables and egg consumption in the last 7 d. About half of children (53·4 %) did not consume eggs in the last 7 d. The odds of children consuming eggs were 4·33 ( < 0·002) times higher when their caregivers had some college education compared with no education. Wealth was positively (OR, 1·13, = 0·029) and household food insecurity was negatively (OR, 0·96, = 0·117) associated with child egg consumption. Purchasing eggs (OR, 9·73, < 0·001) and caregiver's positive behavioural determinants (OR, 1·37, = 0·005) were associated with child egg consumption. The associations of socio-demographic characteristics and economic resources with egg consumption provide evidence of partial mediation through caregiver behaviour and child health. About half of children aged 6-23·9 months consumed eggs. Availability of eggs in households, mainly through purchase, was strongly associated with egg consumption. Education of caregivers and household heads and economic resources were associated with egg consumption and may operate through caregiver behaviour.

Traditional food markets are a key node of resilient food systems worldwide. However, improper food handling and limitations in market structures may result in foodborne disease. This study assessed the decision-making of consumers and vendors in traditional markets to identify opportunities to reduce foodborne contamination and exposure. A cross-sectional survey of 150 consumers and 150 vendors was conducted in Sidama, Ethiopia, in July–August 2022 to investigate practices, behavior drivers, and enabling environment factors relevant to food safety. Descriptive statistics were used to summarize demographics and behavior variables, and the Poverty Probability Index for socioeconomic status. Women consumers were the primary deciders for what food to buy. Of those surveyed, 26% of vendors and 19% of consumers lived below $3.20 USD/day. Consumers choose to purchase food based on price, food quality, vendor personality, and food safety (assessed using visual and sensory cues). Vendors were unconcerned about foodborne disease (73%) and attributed business success to food quality, their personality, and offering discounts. Salience and demand for food quality, as well as trusted relationships, could be leveraged as business incentives for vendors to adopt food safety practices and to increase consumers’ preference for safer food and ability to identify it.

Using a quasi‐experimental design, our study aimed to determine the effectiveness of the ‘Eggs Make Kids Sharp & Bright and Strong & Active’ demand‐creation campaign in Nigeria. The intervention arm received emotionally compelling radio and television advertisements about eggs, and was exposed to promotional activities and advertising about eggs at points of purchase, schools and health facilities; the comparison arm received no intervention. Children 6–59 months of age (intervention: n = 1359; comparison: n = 1485) were assessed 14 months apart. Intent‐to‐treat analyses with analysis of covariance method assessed the impact of the intervention on caregivers' behaviour towards eggs, caregivers' willingness to pay for eggs, availability of eggs in households, and consumption of eggs by children 6–59 months of age. Analyses were adjusted for possible confounders and perceived effects of COVID‐19 on finances and food consumption. Compared to the comparison arm, the intervention arm showed a greater prevalence of household egg acquisition (odds ratio = 1.34, p < 0.0001), and larger improvements in caregiver self‐efficacy (β = 0.242, p = 0.004) and intent to feed eggs to children (β = 0.080, p = 0.021). No effects were found on children's egg consumption or caregivers' reported willingness to pay for eggs. The lack of impact on child egg consumption despite increased acquisition of eggs and caregiver self‐efficacy suggests that other barriers to child consumption may exist. Additional research should further investigate factors that may influence intrahousehold distribution of eggs and whether these may also influence other nutritious foods. Key messages An emotionally engaged demand creation campaign around eggs resulted in small improvements in household acquisition of eggs and caregivers' self‐efficacy and intent to feed eggs to their child 6–59 months of age, but did not improve egg consumption in children. Economic hardships imposed by the COVID‐19 pandemic and low interpersonal communication associated with the campaign may have contributed to the lack of effects of egg consumption. Demand generation activities as stand‐alone activities are insufficient in improving egg consumption among children 6–59 months of age in this context.

We estimated the cost-effectiveness of home fortification with micronutrient powder delivered in a sales-based programme in reducing the prevalence of Fe deficiency anaemia among children 6-59 months in Bangladesh. Cross-sectional interviews with local and central-level programme staff and document reviews were conducted. Using an activity-based costing approach, we estimated start-up and implementation costs of the programme. The incremental cost per anaemia case averted and disability-adjusted life years (DALY) averted were estimated by comparing the home fortification programme and no intervention scenarios. The home fortification programme was implemented in 164 upazilas (sub-districts) in Bangladesh. Caregivers of child 6-59 months and BRAC staff members including community health workers were the participants for this study. The home fortification programme had an estimated total start-up cost of 35·46 million BDT (456 thousand USD) and implementation cost of 1111·63 million BDT (14·12 million USD). The incremental cost per Fe deficiency anaemia case averted and per DALY averted was estimated to be 1749 BDT (22·2 USD) and 12 558 BDT (159·3 USD), respectively. Considering per capita gross domestic product (1516·5 USD) as the cost-effectiveness threshold, the home fortification programme was highly cost-effective. The programme coverage and costs for nutritional counselling of the beneficiary were influential parameters for cost per DALY averted in the one-way sensitivity analysis. The market-based home fortification programme was a highly cost-effective mechanism for delivering micronutrients to a large number of children in Bangladesh. The policymakers should consider funding and sustaining large-scale sales-based micronutrient home fortification efforts assuming the clear population-level need and potential to benefit persists.

In Kenya 26% of children under age 5 experience stunted growth, 4% are wasted and 11% are underweight. In pregnant women, the prevalence of iron deficiency is 36% and iron‐deficiency anaemia prevalence is 26%. Previous studies have identified affordability as a key barrier to the intake of nutrients, particularly from animal‐source foods (ASFs). Thus, this study analyzes to what extent the affordability of ASF in Kenya can be improved. It focuses on four ASFs: eggs, milk, chicken and beef. Using a computable general equilibrium model, three policy simulations were undertaken to establish the impact of potential changes on nutritious ASF availability and affordability: a 20% increase in total factor productivity (TFP) for the four products; a 20% TFP increase plus a 25% reduction in trade and transportation margins; and a 20% TFP increase for ASF and maize (a key input in animal feed). Simulations suggest increasing the productivity of the four ASF products would increase their availability and lower consumer prices (up to 17% lower). Household consumption of the four commodities would increase, resulting in improved household dietary diversity. Rural households would gain more compared with urban households. Poor households (the lowest 40%) would register larger welfare (Equivalent Variation) gains than other households in both urban and rural areas. The richest 20% of the population would neither lose nor gain following the policy changes. Reducing transportation costs and trade margins and increasing maize productivity could further reduce the price of ASFs through lower production costs and increased consumption. Key messages Affordability is a key barrier to the consumption of nutritious animal‐source foods (ASFs) in Kenya. We undertook simulations to understand how policy changes would impact ASF affordability and availability. Increasing the supply of ASFs could yield lower prices for these foods. The impact on prices could be magnified if supply increases were accompanied by reduced trade and transportation margins. Intake of ASFs and dietary diversity could increase if prices were lowered.

Quasi-experimental designs are gaining popularity in epidemiology and health systems research—in particular for the evaluation of health care practice, programs, and policy—because they allow strong causal inferences without randomized controlled experiments. We describe the concepts underlying five important quasi-experimental designs: Instrumental Variables, Regression Discontinuity, Interrupted Time Series, Fixed Effects, and Difference-in-Differences designs. We illustrate each of the designs with an example from health research. We then describe the assumptions required for each of the designs to ensure valid causal inference and discuss the tests available to examine the assumptions.