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Researchers interested in causal questions must deal with two sources of error: random error (random deviation from the true mean value of a distribution), and bias (systematic deviance from the true mean value due to extraneous factors). For some causal questions, randomization is not feasible, and observational studies are necessary. Bias poses a substantial threat to the validity of observational research and can have important consequences for health policy developed from the findings. The current piece describes bias and its sources, outlines proposed methods to estimate its impacts in an observational study, and demonstrates how these methods may be used to inform debate on the causal relationship between medically assisted reproduction (MAR) and health outcomes, using cancer as an example. In doing so, we aim to enlighten researchers who work with observational data, especially regarding the health effects of MAR and infertility, on the pitfalls of bias, and how to address them. We hope that, in combination with the provided example, we can convince readers that estimating the impact of bias in causal epidemiologic research is not only important but necessary to inform the development of robust health policy and clinical practice recommendations. [ABSTRACT FROM AUTHOR]

BACKGROUND Family-planning policies have focused on contraceptive approaches to avoid unintended pregnancies, postpone, or terminate pregnancies and mitigate population growth. These policies have contributed to significantly slowing world population growth. Presently, half the countries worldwide exhibit a fertility rate below replacement level. Not including the effects of migration, many countries are predicted to have a population decline of >50% from 2017 to 2100, causing demographic changes with profound societal implications. Policies that optimize chances to have a child when desired increase fertility rates and are gaining interest as a family-building method. Increasingly, countries have implemented child-friendly policies (mainly financial incentives in addition to public funding of fertility treatment in a limited number of countries) to mitigate decreasing national populations. However, the extent of public spending on child benefits varies greatly from country to country. To our knowledge, this International Federation of Fertility Societies (IFFS) consensus document represents the first attempt to describe major disparities in access to fertility care in the context of the global trend of decreasing growth in the world population, based on a narrative review of the existing literature. OBJECTIVE AND RATIONALE The concept of family building , the process by which individuals or couples create or expand their families, has been largely ignored in family-planning paradigms. Family building encompasses various methods and options for individuals or couples who wish to have children. It can involve biological means, such as natural conception, as well as ART, surrogacy, adoption, and foster care. Family-building acknowledges the diverse ways in which individuals or couples can create their desired family and reflects the understanding that there is no one-size-fits-all approach to building a family. Developing education programs for young adults to increase family-building awareness and prevent infertility is urgently needed. Recommendations are provided and important knowledge gaps identified to provide professionals, the public, and policymakers with a comprehensive understanding of the role of child-friendly policies. SEARCH METHODS A narrative review of the existing literature was performed by invited global leaders who themselves significantly contributed to this research field. Each section of the review was prepared by two to three experts, each of whom searched the published literature (PubMed) for peer reviewed full papers and reviews. Sections were discussed monthly by all authors and quarterly by the review board. The final document was prepared following discussions among all team members during a hybrid invitational meeting where full consensus was reached. OUTCOMES Major advances in fertility care have dramatically improved family-building opportunities since the 1990s. Although up to 10% of all children are born as a result of fertility care in some wealthy countries, there is great variation in access to care. The high cost to patients of infertility treatment renders it unaffordable for most. Preliminary studies point to the increasing contribution of fertility care to the global population and the associated economic benefits for society. WIDER IMPLICATIONS Fertility care has rarely been discussed in the context of a rapid decrease in world population growth. Soon, most countries will have an average number of children per woman far below the replacement level. While this may have a beneficial impact on the environment, underpopulation is of great concern in many countries. Although governments have implemented child-friendly policies, distinct discrepancies in access to fertility care remain. [ABSTRACT FROM AUTHOR]

Background The Surveillance and Treatment of Prisoners With Hepatitis C (SToP-C) study demonstrated that scaling up of direct-acting antiviral (DAA) treatment reduced hepatitis C virus (HCV) transmission. We evaluated the cost-effectiveness of scaling up HCV treatment in statewide prison services incorporating long-term outcomes across custodial and community settings. Methods A dynamic model of incarceration and HCV transmission among people who inject drugs (PWID) in New South Wales, Australia, was extended to include former PWID and those with long-term HCV progression. Using Australian costing data, we estimated the cost-effectiveness of scaling up HCV treatment in prisons by 44% (as achieved by the SToP-C study) for 10 years (2021–2030) before reducing to baseline levels, compared to a status quo scenario. The mean incremental cost-effectiveness ratio (ICER) was estimated by comparing the differences in costs and quality-adjusted life-years (QALYs) between the scale-up and status quo scenarios over 40 years (2021–2060) discounted at 5% per annum. Univariate and probabilistic sensitivity analyses were performed. Results Scaling up HCV treatment in the statewide prison service is projected to be cost-effective with a mean ICER of A$12 968/QALY gained. The base-case scenario gains 275 QALYs over 40 years at a net incremental cost of A$3.6 million. Excluding DAA pharmaceutical costs, the mean ICER is reduced to A$6 054/QALY. At the willingness-to-pay threshold of A$50 000/QALY, 100% of simulations are cost-effective at various discount rates, time horizons, and changes of treatment levels in prison and community. Conclusions Scaling up HCV testing and treatment in prisons is highly cost-effective and should be considered a priority in the national elimination strategy. Clinical Trials Registration NCT02064049. [ABSTRACT FROM AUTHOR]

STUDY QUESTION What is the association between a country's level of gender equality and access to ART, as measured through ART utilization? SUMMARY ANSWER ART utilization is associated with a country's level of gender equality even after controlling for the level of development. WHAT IS KNOWN ALREADY Although gender equality is recognized as an important determinant of population health, its association with fertility care, a highly gendered condition, has not been explored. STUDY DESIGN, SIZE, DURATION A longitudinal cross-national analysis of ART utilization in 69 countries during 2002–2014 was carried out. PARTICPANTS/MATERIALS, SETTING, METHODS The Gender Inequality Index (GII), Human Development Index (HDI), and their component indicators were modelled against ART utilization using univariate regression models as well as mixed-effects regression methods (adjusted for country, time, and economic/human development) with multiple imputation to account for missing data. MAIN RESULTS AND THE ROLE OF CHANCE ART utilization is associated with the GII. In an HDI-adjusted analysis, a one standard deviation decrease in the GII (towards greater equality) is associated with a 59% increase in ART utilization. Gross national income per capita, the maternal mortality ratio, and female parliamentary representation were the index components most predictive of ART utilization. LIMITATIONS, REASONS FOR CAUTION Only ART was used rather than all infertility treatments (including less costly and non-invasive treatments such as ovulation induction). This was a country-level analysis and the results cannot be generalized to smaller groups. Not all modelled variables were available for each country across 2002–2014. WIDER IMPLICATIONS OF THE FINDINGS Access to fertility care is central to women's sexual and reproductive health, to women's rights, and to human rights. As gender equality improves, so does access to ART. This relation is likely to be reinforcing and bi-directional, with progress towards global, equitable access to fertility care also improving women's status and participation in societies. STUDY FUNDING/COMPETING INTEREST(S) External funding was not provided for this study. G.D.A. declares consulting fees from Labcorp and CooperSurgical. G.D.A. is the founder and CEO of Advanced Reproductive Care, Inc. as well as the Chair of the International Committee for Monitoring Assisted Reproductive Technologies (ICMART) and the World Endometriosis Research Foundation, both of which are unpaid roles. G.M.C. is an ICMART Board Representative, which is an unpaid role, and no payments are received from ICMART to UNSW, Sydney, or to G.M.C. to undertake this study. O.F. S.D. F.Z.-H. and E.K. report no conflicts of interest. TRIAL REGISTRATION NUMBER N/A. [ABSTRACT FROM AUTHOR]

Study Question: Can we develop a prediction model for the chance of a live birth following the transfer of an embryo created using donated oocytes?, Summary Answer: Three primary models that included patient, past treatment, and cycle characteristics were developed using Australian data to predict the chance of a live birth following the transfer of an embryo created using donated oocytes; these models were well-calibrated to the population studied, achieved reasonable predictive power and generalizability when tested on New Zealand data., What Is Known Already: Nearly 9% of ART embryo transfer cycles performed globally use embryos created using donated oocytes. This percentage rises to one-quarter and one-half in same-sex couples and women aged over 45 years, respectively., Study Design, Size, Duration: This study uses population-based Australian clinical registry data comprising 9384 embryo transfer cycles that occurred between 2015 and 2021 for model development, with an external validation cohort of 1493 New Zealand embryo transfer cycles., Participants/materials, Setting, Methods: Three prediction models were compared that incorporated patient characteristics, but differed in whether they considered use of prior autologous treatment factors and current treatment parameters. We internally validated the models on Australian data using grouped cross-validation and reported several measures of model discrimination and calibration. Variable importance was measured through calculating the change in predictive performance that resulted from variable permutation. The best-performing model was externally validated on data from New Zealand., Main Results and the Role of Chance: The best-performing model had an internal validation AUC-ROC of 0.60 and Brier score of 0.20, and external validation AUC-ROC of 0.61 and Brier score of 0.23. While these results indicate ∼15% less discriminatory ability compared to models assessed on an autologous cohort from the same population the performance of the models was clearly statistically significantly better than random, demonstrated generalizability, and was well-calibrated to the population studied. The most important variables for predicting the chance of a live birth were the oocyte donor age, the number of prior oocyte recipient embryo transfer cycles, whether the transferred embryo was cleavage or blastocyst stage and oocyte recipient age. Of lesser importance were the oocyte-recipient parity, whether donor or partner sperm was used, the number of prior autologous embryo transfer cycles and the number of embryos transferred., Limitations, Reasons for Caution: The models had relatively weak discrimination suggesting further features need to be added to improve their predictive power. Variation in donor oocyte cohorts across countries due to differences such as whether anonymous and compensated donation are allowed may necessitate the models be recalibrated prior to application in non-Australian cohorts., Wider Implications of the Findings: These results confirm the well-established importance of oocyte age and ART treatment history as the key prognostic factors in predicting treatment outcomes. One of the developed models has been incorporated into a consumer-facing website (YourIVFSuccess.com.au/Estimator) to allow patients to obtain personalized estimates of their chance of success using donor oocytes., Study Funding/competing Interest(s): This research was funded by the Australian government as part of the Medical Research Future Fund (MRFF) Emerging Priorities and Consumer Driven Research initiative: EPCD000007. L.R. declares personal consulting fees from Abbott and Merck, lecture fees from Abbott, receipt of an educational grant from Merck, past presidency of the Fertility Society of Australia & New Zealand and World Endometriosis Society and being a minor shareholder in Monash IVF Group (ASX:MVF). G.M.C. declares receipt of Australian government grant funding for the research study and the development and maintenance of the YourIVFSuccess website. O.F., J.N., and A.P. report no conflicts of interest., Trial Registration Number: N/A., (© The Author(s) 2024. Published by Oxford University Press on behalf of European Society of Human Reproduction and Embryology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Background: The Surveillance and Treatment of Prisoners With Hepatitis C (SToP-C) study demonstrated that scaling up of direct-acting antiviral (DAA) treatment reduced hepatitis C virus (HCV) transmission. We evaluated the cost-effectiveness of scaling up HCV treatment in statewide prison services incorporating long-term outcomes across custodial and community settings., Methods: A dynamic model of incarceration and HCV transmission among people who inject drugs (PWID) in New South Wales, Australia, was extended to include former PWID and those with long-term HCV progression. Using Australian costing data, we estimated the cost-effectiveness of scaling up HCV treatment in prisons by 44% (as achieved by the SToP-C study) for 10 years (2021-2030) before reducing to baseline levels, compared to a status quo scenario. The mean incremental cost-effectiveness ratio (ICER) was estimated by comparing the differences in costs and quality-adjusted life-years (QALYs) between the scale-up and status quo scenarios over 40 years (2021-2060) discounted at 5% per annum. Univariate and probabilistic sensitivity analyses were performed., Results: Scaling up HCV treatment in the statewide prison service is projected to be cost-effective with a mean ICER of A$12 968/QALY gained. The base-case scenario gains 275 QALYs over 40 years at a net incremental cost of A$3.6 million. Excluding DAA pharmaceutical costs, the mean ICER is reduced to A$6 054/QALY. At the willingness-to-pay threshold of A$50 000/QALY, 100% of simulations are cost-effective at various discount rates, time horizons, and changes of treatment levels in prison and community., Conclusions: Scaling up HCV testing and treatment in prisons is highly cost-effective and should be considered a priority in the national elimination strategy., Clinical Trials Registration: NCT02064049., Competing Interests: Potential conflicts of interest. G. J. D. is a consultant/advisor for and has received research grants from Gilead, AbbVie, Merck, Bristol-Myers Squibb, and Cepheid. A. R. L. has received investigator-initiated research grants from Gilead, AbbVie, Merck, and Bristol-Myers Squibb. J. G. is a consultant/advisor and has received research grants from Gilead, AbbVie, Merck, and Cepheid. P. V. has received investigator-initiated untied grants from Gilead and honoraria from Gilead and Merck. N. K. M. has received unrestricted research grants from Gilead and Merck. All other authors report no potential conflicts., (© The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America.)