A comparison of reweighting estimators of average treatment effects in real world populations

Regulatory agencies typically evaluate the efficacy and safety of new interventions and grant commercial approval based on randomized controlled trials (RCTs). Other major healthcare stakeholders, such as insurance companies and health technology assessment agencies, while basing initial access and reimbursement decisions on RCT results, are also keenly interested in whether results observed in idealized trial settings will translate into comparable outcomes in real world settings—that is, into so-called “real world” effectiveness. Unfortunately, evidence of real world effectiveness for new interventions is not available at the time of initial approval. To bridge this gap, statistical methods are available to extend the estimated treatment effect observed in a RCT to a target population. The generalization is done by weighting the subjects who participated in a RCT so that the weighted trial population resembles a target population. We evaluate a variety of alternative estimation and weight construction procedures using both simulations and a real world data example using two clinical trials of an investigational intervention for Alzheimer's disease. Our results suggest an optimal approach to estimation depends on the characteristics of source and target populations, including degree of selection bias and treatment effect heterogeneity.     

Unpaid labour and territorial extraction in digital value networks

Production in knowledge and data-intensive industries is powered by work that can, in theory, be done from anywhere, via cloudwork platforms. Cloudwork platforms govern data value chains in distinct ways to concentrate power and extract value at the global scale. We argue that unpaid labour is a systemic mechanism of accumulation in these digital value networks. In this paper we demonstrate how it is tied to platform business models and facilitated by elements of platform governance including monopsony power, a high degree of spatial flexibility in sourcing labour, regulatory unaccountability and digital enclosure. We draw on a survey of 699 workers on 14 platforms in 74 countries to show that unpaid labour is an engine of South–North value extraction, and workers in the global South perform more unpaid labour than counterparts in the global North. Our findings have important ramifications our understanding of the changing international division of labour and platform capitalism.     

Statistical Artifacts in the Ratio of Discrete Quantities

The ratio is a familiar statistic, but it is often misused. One frequently overlooked problem occurs when ratioing two discrete (digitized) variables. Fine structure appears in the histogram of the ratio that can be very subtle, or can sometimes even dominate the histogram. It disappears when the numerator and/or denominator become continuous. This statistical artifact is not a binning error, nor is it removed by taking more data. It is important to be aware of the artifact in order to avoid misinterpretation of ratio data. We provide examples of the statistical artifact (including one from baseball) and discuss ways to avoid or minimize the problems it can cause.     

Understanding Ethnic Small Business: A Case Study of Marrickville

Ethnic small businesses are an increasingly important feature of economic life in Australian cities. Which groups are most likely to go into this sector, and what are the factors which make for ‘success’? What is the price for survival in terms of working conditions and family life, and what are the fruits of success? These are some of the questions being investigated in a two-year study of ethnic small business in the Sydney region. This paper provides the first report from the study, examining the development of Greek and Vietnamese businesses in the inner suburb of Marrickville.     

How Important is Selection? Experimental VS. Non‐Experimental Measures of the Income Gains from Migration

How much do migrants stand to gain in income from moving across borders? Answering this question is complicated by non‐random selection of migrants from the general population, which makes it hard to obtain an appropriate comparison group of non‐migrants. New Zealand allows a quota of Tongans to immigrate each year with a random ballot used to choose among the excess number of applicants. A unique survey conducted by the authors allows experimental estimates of the income gains from migration to be obtained by comparing the incomes of migrants to those who applied to migrate, but whose names were not drawn in the ballot, after allowing for the effect of non‐compliance among some of those whose names were drawn. We also conducted a survey of individuals who did not apply for the ballot. Comparing this non‐applicant group to the migrants enables assessment of the degree to which non‐experimental methods can provide an unbiased estimate of the income gains from migration. We find evidence of migrants being positively selected in terms of both observed and unobserved skills. As a result, non‐experimental methods other than instrumental variables are found to overstate the gains from migration by 20–82%, with difference‐in‐differences and bias‐adjusted matching estimators performing best among the alternatives to instrumental variables. (JEL: J61, F22, C21)