Instrumental Variables Estimation in Political Science: A Readers’ Guide

The use of instrumental variables regression in political science has evolved from an obscure technique to a staple of the political science tool kit. Yet the surge of interest in the instrumental variables method has led to implementation of uneven quality. After providing a brief overview of the method and the assumptions on which it rests, we chart the ways in which these assumptions are invoked in practice in political science. We review more than 100 articles published in the American Journal of Political Science, the American Political Science Review, and World Politics over a 24‐year span. We discuss in detail two noteworthy applications of instrumental variables regression, calling attention to the statistical assumptions that each invokes. The concluding section proposes reporting standards and provides a checklist for readers to consider as they evaluate applications of this method.     

Pulling the Levers: Transformational Leadership,Public Service Motivation,and Mission Valence

This article contributes to our understanding of public service motivation and leadership by investigating ways in which organizational leaders can reinforce and even augment the potential effects of public service motivation on employees’ attraction to the organization’s mission (mission valence). The results contribute to two research questions. First, the findings provide new evidence on the sources of public service motivation. The authors find that transformational leadership is an organizational factor associated with higher public service motivation. Second, the article examines the relationship between transformational leadership and mission valence. The authors find that transformational leadership has an important indirect effect on mission valence through its influence on clarifying organizational goals and fostering public service motivation.     

Does Involvement in Performance Management Routines Encourage Performance Information Use? Evaluating GPRA and PART

The Government Performance and Results Act (GPRA) of 1993 and the George W. Bush administration’s Program Assessment Rating Tool (PART) established new routines that were intended to foster performance management practices. Using data from two surveys, the authors find that the involvement of agency employees in GPRA processes and PART reviews generally had little direct effect on performance information use once other factors are accounted for. The main exception is that managerial involvement in GPRA processes and PART reviews is associated with the use of performance data to refine measures and goals. This reflects the limits of government‐wide reform efforts that depend on difficult‐to‐observe bureaucratic behavior. The authors also find that a series of organizational factors—leadership commitment to results, learning routines led by supervisors, the motivational nature of the task, and the ability to link measures to actions—are positive predictors of performance information use.     

Detecting Spillover Effects: Design and Analysis of Multilevel Experiments

Interpersonal communication presents a methodological challenge and a research opportunity for researchers involved in field experiments. The challenge is that communication among subjects blurs the line between treatment and control conditions. When treatment effects are transmitted from subject to subject, the stable unit treatment value assumption (SUTVA) is violated, and comparison of treatment and control outcomes may provide a biased assessment of the treatment’s causal influence. Social scientists are increasingly interested in the substantive phenomena that lead to SUTVA violations, such as communication in advance of an election. Experimental designs that gauge SUTVA violations provide useful insights into the extent and influence of interpersonal communication. This article illustrates the value of one such design, a multilevel experiment in which treatments are randomly assigned to individuals and varying proportions of their neighbors. After describing the theoretical and statistical underpinnings of this design, we apply it to a large‐scale voter‐mobilization experiment conducted in Chicago during a special election in 2009 using social‐pressure mailings that highlight individual electoral participation. We find some evidence of within‐household spillovers but no evidence of spillovers across households. We conclude by discussing how multilevel designs might be employed in other substantive domains, such as the study of deterrence and policy diffusion.     

Evaluation of pediatric skull fracture imaging techniques

Radiologic imaging is crucial in the diagnosis of skull fracture, but there is some doubt as to whether different imaging modalities can accurately identify fractures present on a human skull. While studies have been performed to evaluate the efficacy of radiologic imaging at other anatomical locations, there have been no systematic studies comparing various CT techniques, including high resolution imaging with and without 3D reconstructions to conventional radiologic imaging in children, we investigated which imaging modalities: high-resolution CT scan with 3D projections, clinical-resolution CT scans or X-rays, best showed fracture occurrence in a pediatric human cadaver skull by having an expert pediatric radiologist examine radiologic images from fractured skulls. The skulls used were taken from pediatric cadavers ranging in age from 5 months to 16 years. We evaluated the sensitivity and specificity for the imaging modalities using dissection findings as the gold standard. We found that high-resolution CT scans with 3D projections and conventional CT provided the most accurate fracture diagnosis (single-fracture sensitivity of 71%) followed by X-rays (single-fracture sensitivity of 63%). Linear fractures outsider the region of the sutures were more identifiable than diastatic fractures, though the incidence of false positives was greater for linear fractures. In the two cases where multiple fractures were present on the same anatomical skull location, the radiologist was less likely to identify the presence of additional fractures than a single fracture. Overall, the high-resolution and clinical-resolution CT scans had the similar accuracy for detecting skull fractures while the use of the X-ray was both less accurate and had a lower specificity.     

Social Network Analysis and the Diffusion of the Strict Liability Rule for Manufacturing Defects, 1963–87

This article reports the results of a study that uses social network analysis to compare the persuasiveness of legal precedents in the diffusion of the strict liability rule for manufacturing defects. This new study tests which legal precedents were most influential and also whether certain state judicial variables influenced the diffusion process. The results are striking. The federal circuit regions appear to define an important reference group in the diffusion process, and social network effects dominate economic and political variables. In addition, the de facto separation of powers in the enactment of new state legislation appears to influence courts' propensities to adopt the strict liability rule. When the executive and legislative branches were controlled by the same political party, regardless of whether it was Republican or Democratic, state courts were more inclined to adopt the strict liability rule.     

A conversation with Donald Berwick on implementing national health reform

Michael Birnbaum interviews Donald Berwick shortly after his departure from the Centers for Medicare and Medicaid Services about the national health care landscape. Berwick discusses the strategic vision, policy levers, operational challenges, and political significance of federal health care reform. He rejects the notion that the Affordable Care Act represents a government takeover of health care financing or service delivery but says the law's Medicaid expansion and its creation of health benefit exchanges present a "watershed moment for American federalism." Berwick argues that the solution to Medicare's cost-containment challenge lies in quality improvement. He is optimistic that accountable care organizations can deliver savings and suggests that shifting risk downstream to providers throws the health insurance model into question. Finally, looking to the future, Berwick sees a race against time to make American health care more affordable.     

STR melting curve analysis as a genetic screening tool for crime scene samples

In this proof-of-concept study, high-resolution melt curve (HRMC) analysis was investigated as a postquantification screening tool to discriminate human CSF1PO and THO1 genotypes amplified with mini-STR primers in the presence of SYBR Green or LCGreen Plus dyes. A total of 12 CSF1PO and 11 HUMTHO1 genotypes were analyzed on the LightScanner HR96 and LS-32 systems and were correctly differentiated based upon their respective melt profiles. Short STR amplicon melt curves were affected by repeat number, and single-source and mixed DNA samples were additionally differentiated by the formation of heteroduplexes. Melting curves were shown to be unique and reproducible from DNA quantities ranging from 20 to 0.4 ng and distinguished identical from nonidentical genotypes from DNA derived from different biological fluids and compromised samples. Thus, a method is described which can assess both the quantity and the possible probative value of samples without full genotyping.