Numerous observational studies have attempted to identify risk factors for infection with SARS-CoV-2 and COVID-19 disease outcomes. Studies have used datasets sampled from patients admitted to hospital, people tested for active infection, or people who volunteered to participate. Here, we highlight the challenge of interpreting observational evidence from such non-representative samples. Collider bias can induce associations between two or more variables which affect the likelihood of an individual being sampled, distorting associations between these variables in the sample. Analysing UK Biobank data, compared to the wider cohort the participants tested for COVID-19 were highly selected for a range of genetic, behavioural, cardiovascular, demographic, and anthropometric traits. We discuss the mechanisms inducing these problems, and approaches that could help mitigate them. While collider bias should be explored in existing studies, the optimal way to mitigate the problem is to use appropriate sampling strategies at the study design stage.

Acknowledgements: We would like to thank the editor, Mike Pratt, and the three anonymous reviewers for their insightful comments. We would also like to acknowledge the help we received from Paula Jarzabkowski and members of OTREG on earlier drafts, and the support of the Novak Druce Center for Professional Service Firms at the University of Oxford. 2 FROM PRACTICE TO FIELD: A MULTI-LEVEL MODEL OF PRACTICE-DRIVEN INSTITUTIONAL CHANGE ABSTRACTThis paper develops a model of practice-driven institutional change; that is, change that originates in the everyday work of individuals, but results in a shift in field-level logic. In demonstrating how improvisations at work can generate institutional change, we attend to the earliest moments of change that extant research neglects; and we contrast existing accounts that focus on active entrepreneurship and the contested nature of change. We outline the specific mechanisms by which change emerges from everyday work, becomes justified, and diffuses within the organization and field, as well as precipitating and enabling dynamics that trigger and condition these mechanisms.3

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Estimates from Mendelian randomization studies of unrelated individuals can be biased due to uncontrolled confounding from familial effects. Here we describe methods for withinfamily Mendelian randomization analyses and use simulation studies to show that familybased analyses can reduce such biases. We illustrate empirically how familial effects can affect estimates using data from 61,008 siblings from the Nord-Trøndelag Health Study and UK Biobank and replicated our findings using 222,368 siblings from 23andMe. Both Mendelian randomization estimates using unrelated individuals and within family methods reproduced established effects of lower BMI reducing risk of diabetes and high blood pressure. However, while Mendelian randomization estimates from samples of unrelated individuals suggested that taller height and lower BMI increase educational attainment, these effects were strongly attenuated in within-family Mendelian randomization analyses. Our findings indicate the necessity of controlling for population structure and familial effects in Mendelian randomization studies.

Purpose – The purpose of this paper is to examine how a system of human resource management (HRM) practices, labelled high-performance work systems (HPWS), influences organizational innovation in professional service firms (PSFs). In this study, innovation in PSFs is seen as an indicator of firm performance and is calculated as the revenue per person generated from new clients and new services, respectively. Design/methodology/approach – Quantitative data were collected from 195 managing partners, HR managers or experienced Partners in 120 Irish accounting firms. Hierarchical regression analysis was used to test the hypotheses. Findings – The analysis results indicate strong support for the mediating role of employees’ innovative work behaviours in the relationship between HPWS and two types of PSFs’ innovation performance. Practical implications – Managers need to effectively adopt and implement innovation-based HRM practices to encourage and support employees’ creative thinking and innovation. Through the adoption and utilization of these practices managers can enhance the firm’s innovation and its performance. Originality/value – This study contributes to our understanding of the link between HRM and firm innovation by explicating a pathway between these variables. This study also generalizes consistent findings on the HRM-firm innovation relationship to a different context, i.e. PSFs.

Heritability, genetic correlation, and genetic associations estimated from samples of unrelated individuals are often perceived as confirmation that genotype causes the phenotype(s). However, these estimates can arise from indirect mechanisms due to population phenomena including population stratification, dynastic effects, and assortative mating. We introduce these, describe how they can bias or inflate genotype-phenotype associations, and demonstrate methods that can be used to assess their presence. Using data on educational achievement and parental socioeconomic position as an exemplar, we demonstrate that both heritability and genetic correlation may be biased estimates of the causal contribution of genotype. These results highlight the limitations of genotype-phenotype estimates obtained from samples of unrelated individuals. Use of these methods in combination with family-based designs may offer researchers greater opportunities to explore the mechanisms driving genotype-phenotype associations and identify factors underlying bias in estimates.

Professional service fi rms (PSFs) play an important role in the knowledge-based economy. Their success is highly dependent on their people, the knowledge resources they possess, and how they use these resources. However, how to systematically manage human resources to attain high performance is not fully understood. This study addresses this issue by investigating the linkage mechanisms through which high-performance work systems (HPWS) infl uence the performance of PSFs. We integrate resource-based and dynamic capability theories in order to identify and investigate two intervening mechanisms that link HR practices to fi rm performance. The fi rst mechanism is the intellectual capital resources comprising the human, social, and organizational capital that HPWS create. The second mechanism is the uses to which both HPWS and resources can be applied, operationalized as organizational ambidexterity, the simultaneous exploitation of existing knowledge and exploration of new knowledge. These mechanisms are hypothesized to link HPWS to fi rm performance in the form of a practicesresources-uses-performance linkage model. Results from a longitudinal study of 93 accounting fi rms support this linkage model. © 2015 Wiley Periodicals, Inc.Keywords: high-performance work systems; professional service fi rms; organizational resources and uses; fi rm performance; linkages model P rofessional service firms (PSFs) are knowledge intensive organizations requiring a highly educated workforce to provide customized solutions to clients (Greenwood, Li, Prakash, & Deephouse, 2005;Maister, 1993; von Nordenflycht, 2010). The primary assets of PSFs are the knowledge and capabilities embedded in their professional staff (Løwendahl, 2000). The success of PSFs such as accounting, consulting, and law firms largely depends on their human resources, although only a few studies address their human resource issues (e.g., Fu, 1991) and dynamic capability theory (Teece, Pisano, & Shuen, 1997). The RBV argues that the firm's competitive advantage lies in its valuable, rare, imperfectly imitable, and nonsubstitutable resources. HR practices themselves are not a direct source of competitive advantage. Rather, advantage derives from the contributions made by people selected, trained, and developed through such practices. In particular, it is the human and social capital that HPWS creates that provide firms the means to achieve superior competitive performance (e.g., Messersmith & Guthrie, 2010;Takeuchi, Lepak, Wang, & Takeuchi, 2007;Youndt et al., 1996). Intellectual capital resources including human capital (Becker, 1964;O'Sullivan & Sheffrin, 1998), social capital (Burt, 1992;Nahapiet & Ghoshal, 1998), and organizational capital (Subramaniam & Youndt, 2005;Youndt, Subramaniam, & Snell, 2004) are particularly important in knowledge-based PSFs. Below, we review the literature and propose specific hypotheses regarding the effects HPWS dimensions have on these distinct forms of capital.The mere possession of resources is inadequate in understanding fir...

154Abstract Mendelian randomization (MR) is a widely-used method for causal inference using genetic data.Mendelian randomization studies of unrelated individuals may be susceptible to bias from family structure, for example, through dynastic effects which occur when parental genotypes directly affect offspring phenotypes. Here we describe methods for within-family Mendelian randomization and through simulations show that family-based methods can overcome bias due to dynastic effects. We illustrate these issues empirically using data from 61,008 siblings from the UK Biobank and Nord-Trøndelag Health Study. Both within-family and populationbased Mendelian randomization analyses reproduced established effects of lower BMI reducing risk of diabetes and high blood pressure. However, while MR estimates from population-based samples of unrelated individuals suggested that taller height and lower BMI increase educational attainment, these effects largely disappeared in within-family MR analyses. We found differences between population-based and within-family based estimates, indicating the importance of controlling for family effects and population structure in Mendelian randomization studies.