Social scientists are often interested in testing multiple causal mechanisms through which a treatment affects outcomes. A predominant approach has been to use linear structural equation models and examine the statistical significance of the corresponding path coefficients. However, this approach implicitly assumes that the multiple mechanisms are causally independent of one another. In this article, we consider a set of alternative assumptions that are sufficient to identify the average causal mediation effects when multiple, causally related mediators exist. We develop a new sensitivity analysis for examining the robustness of empirical findings to the potential violation of a key identification assumption. We apply the proposed methods to three political psychology experiments, which examine alternative causal pathways between media framing and public opinion. Our analysis reveals that the validity of original conclusions is highly reliant on the assumed independence of alternative causal mechanisms, highlighting the importance of proposed sensitivity analysis. All of the proposed methods can be implemented via an open source R package, mediation.

Social scientists generally enjoy substantial latitude in selecting measures and models for hypothesis testing. Coupled with publication and related biases, this latitude raises the concern that researchers may intentionally or unintentionally select models that yield positive findings, leading to an unreliable body of published research. To combat this “fishing” problem in medical studies, leading journals now require preregistration of designs that emphasize the prior identification of dependent and independent variables. However, we demonstrate here that even with this level of advanced specification, the scope for fishing is considerable when there is latitude over selection of covariates, subgroups, and other elements of an analysis plan. These concerns could be addressed through the use of a form of comprehensive registration. We experiment with such an approach in the context of an ongoing field experiment for which we drafted a complete “mock report” of findings using fake data on treatment assignment. We describe the advantages and disadvantages of this form of registration and propose that a comprehensive but nonbinding approach be adopted as a first step to combat fishing by social scientists. Likely effects of comprehensive but nonbinding registration are discussed, the principal advantage being communication rather than commitment, in particular that it generates a clear distinction between exploratory analyses and genuine tests.

Political knowledge research faces a problem, perhaps even a crisis. For two decades, the American National Election Studies asked open-ended questions about political knowledge and coded answers using procedures that are neither reliable nor replicable and that were never shown to be optimally valid. Consequently, conclusions based on these widely used measures of the public's competence are in doubt. This article presents several new and overdue methodological improvements: coding knowledge data using formal and specific coding rules based on a substantive rationale for the validity of the codes, recognizing partially correct answers, using multiple coders working independently, using machine coding, and testing reliability and validity. The new methods are an improvement because they are transparent and replicable and they produce valid and extremely reliable knowledge data. Further, machine coding produces codes nearly identical to those from a team of human coders, at much lower cost.

Politics and political conflict often occur in the written and spoken word. Scholars have long recognized this, but the massive costs of analyzing even moderately sized collections of texts have hindered their use in political science research. Here lies the promise of automated text analysis: it substantially reduces the costs of analyzing large collections of text. We provide a guide to this exciting new area of research and show how, in many instances, the methods have already obtained part of their promise. But there are pitfalls to using automated methods—they are no substitute for careful thought and close reading and require extensive and problem-specific validation. We survey a wide range of new methods, provide guidance on how to validate the output of the models, and clarify misconceptions and errors in the literature. To conclude, we argue that for automated text methods to become a standard tool for political scientists, methodologists must contribute new methods and new methods of validation.

Valid comparisons of group scores on additive measures such as political knowledge scales require that the conditional response probabilities for individuals on the observed items be invariant across groups after controlling for their overall level of the latent trait of interest. Using a multi-group confirmatory factor analysis of knowledge items drawn from American National Election Studies, we find that the scales used in recent research are not sufficiently invariant for valid comparisons across a host of theoretically important grouping variables. We demonstrate that it is possible to construct valid invariant scales using a subset of items and show the impact of invariance by comparing results from the valid and invalid scales. We provide an analysis of differential item functioning based on grouping variables commonly used in political science research to explore the utility of each item in the construction of valid knowledge scales. An application of the VTT suggests it is more appropriate to conceive of these items as effects of a latent variable rather than cause or formative indicators. These results suggest that models attempting to explain apparent knowledge gaps between subgroups have been unsuccessful because previously constructed scales were validated by fiat.

Survey researchers avoid using large multi-item scales to measure latent traits due to both the financial costs and the risk of driving up nonresponse rates. Typically, investigators select a subset of available scale items rather than asking the full battery. Reduced batteries, however, can sharply reduce measurement precision and introduce bias. In this article, we present computerized adaptive testing (CAT) as a method for minimizing the number of questions each respondent must answer while preserving measurement accuracy and precision. CAT algorithms respond to individuals' previous answers to select subsequent questions that most efficiently reveal respondents' positions on a latent dimension. We introduce the basic stages of a CAT algorithm and present the details for one approach to item selection appropriate for public opinion research. We then demonstrate the advantages of CAT via simulation and empirically comparing dynamic and static measures of political knowledge.

Automated and statistical methods for estimating latent political traits and classes from textual data hold great promise, because virtually every political act involves the production of text. Statistical models of natural language features, however, are heavily laden with unrealistic assumptions about the process that generates these data, including the stochastic process of text generation, the functional link between political variables and observed text, and the nature of the variables (and dimensions) on which observed text should be conditioned. While acknowledging statistical models of latent traits to be “wrong,” political scientists nonetheless treat their results as sufficiently valid to be useful. In this article, we address the issue of substantive validity in the face of potential model failure, in the context of unsupervised scaling methods of latent traits. We critically examine one popular parametric measurement model of latent traits for text and then compare its results to systematic human judgments of the texts as a benchmark for validity.

Social scientists long have debated how closely their research methods resemble the pure, classical ideal: sequentially (and absent pejorative “data snooping”) formulate a theory; develop empirically falsifiable hypotheses; collect data; and conduct the appropriate statistical tests. Meanwhile, in private quarters, they acknowledged that true research seldom proceeds in this fashion. Rather, in the event, the world is observed, data are collected, hypotheses formed, tests conducted, more data collected, and hypotheses revised (e.g., the classic Bernal 1974). Results are collected by the field's scientists into a body of knowledge that defines “known science” and sets the accepted boundaries for future research. Kuhn (1970) labeled this a paradigm. Occasionally, he argued, results appear that lie outside the bounds of the extant paradigm—then, innovation occurs.

The articles included in this issue's symposium discuss “registration” of empirical studies. The purpose is to reduce “publication bias,” that is, to prevent the scientific equivalent of schoolboy cheating: reporting tests of hypotheses that became evident only after the data were in hand. Registration has little power against the type of research fraud that is discovered from time to time. There are costs, however, when scientists operating within an accepted paradigm discourage researchers from exploring and reporting any/all relationships and correlations in a data set.

Methods for analysis of network dynamics have seen great progress in the past decade. This article shows how Dynamic Network Logistic Regression techniques (a special case of the Temporal Exponential Random Graph Models) can be used to implement decision theoretic models for network dynamics in a panel data context. We also provide practical heuristics for model building and assessment. We illustrate the power of these techniques by applying them to a dynamic blog network sampled during the 2004 US presidential election cycle. This is a particularly interesting case because it marks the debut of Internet-based media such as blogs and social networking web sites as institutionally recognized features of the American political landscape. Using a longitudinal sample of all Democratic National Convention/Republican National Convention—designated blog citation networks, we are able to test the influence of various strategic, institutional, and balance-theoretic mechanisms as well as exogenous factors such as seasonality and political events on the propensity of blogs to cite one another over time. Using a combination of deviance-based model selection criteria and simulation-based model adequacy tests, we identify the combination of processes that best characterizes the choice behavior of the contending blogs.

Political scientists are often interested in estimating causal effects. Identification of causal estimates with observational data invariably requires strong untestable assumptions. Here, we outline a number of the assumptions used in the extant empirical literature. We argue that these assumptions require careful evaluation within the context of specific applications. To that end, we present an empirical case study on the effect of Election Day Registration (EDR) on turnout. We show how different identification assumptions lead to different answers, and that many of the standard assumptions used are implausible. Specifically, we show that EDR likely had negligible effects in the states of Minnesota and Wisconsin. We conclude with an argument for stronger research designs.

Much politico-economic research on individuals' preferences is cross-sectional and does not model dynamic aspects of preference or attitude formation. I present a Bayesian dynamic panel model, which facilitates the analysis of repeated preferences using individual-level panel data. My model deals with three problems. First, I explicitly include feedback from previous preferences taking into account that available survey measures of preferences are categorical. Second, I model individuals' initial conditions when entering the panel as resulting from observed and unobserved individual attributes. Third, I capture unobserved individual preference heterogeneity both via standard parametric random effects and a robust alternative based on Bayesian nonparametric density estimation. I use this model to analyze the impact of income and wealth on preferences for government intervention using the British Household Panel Study from 1991 to 2007.

The traditional system of scientific and scholarly publishing is breaking down in two different directions.

This article presents a new method of reconstructing actors' political positions from coded political texts. It is based on a model that combines a dynamic perspective on actors' political positions with a probabilistic account of how these positions are translated into emphases of policy topics in political texts. In the article it is shown how model parameters can be estimated based on a maximum marginal likelihood principle and how political actors' positions can be reconstructed using empirical Bayes techniques. For this purpose, a Monte Carlo Expectation Maximization algorithm is used that employs independent sample techniques with automatic Monte Carlo sample size adjustment. An example application is given by estimating a model of an economic policy space and a noneconomic policy space based on the data from the Comparative Manifesto Project. Parties' positions in policy spaces reconstructed using these models are made publicly available for download.

Multilevel regression and poststratification (MRP) is a method to estimate public opinion across geographic units from individual-level survey data. If it works with samples the size of typical national surveys, then MRP offers the possibility of analyzing many political phenomena previously believed to be outside the bounds of systematic empirical inquiry. Initial investigations of its performance with conventional national samples produce generally optimistic assessments. This article examines a larger number of cases and a greater range of opinions than in previous studies and finds substantial variation in MRP performance. Through empirical and Monte Carlo analyses, we develop an explanation for this variation. The findings suggest that the conditions necessary for MRP to perform well will not always be met. Thus, we draw a less optimistic conclusion than previous studies do regarding the use of MRP with samples of the size found in typical national surveys.

Utilizing hierarchical cluster analysis, a new measure of democracy, the DCC index, is proposed and constructed from five popular indices of democracy (Freedom House, Polity IV, Vanahanen's index of democratization, Cheibub et al.'s index of democracy and dictatorship, and the Cingranelli-Richards index of electoral self-determination). The DCC was used to classify the regime types for twenty-four countries in the Americas and thirty-nine countries in Europe over a thirty-year period. The results indicated that democracy is a latent class variable. Sensitivity and specificity analyses were conducted for the five existing democracy indices as well as the newly proposed Unified Democracy Scores index and a predicted DCC score. This analysis revealed significant problems with existing measures. Overall, the predicted DCC index attained the highest level of accuracy although one other index achieved high levels of accuracy in identifying nondemocracies.

This article offers a new explanation for the results of twin studies in political science that supposedly disclose a genetic basis for political traits. I argue that identical twins tend to be more alike than nonidentical twins because the former are more similarly affected by the same environmental conditions, but the content of those greater trait similarities is nevertheless completely malleable and determined by particular environments. The twin studies method thus can neither prove nor refute the argument for a genetic basis of political traits such as liberal and conservative preferences or voting turnout. The meaning of heritability estimates results in twin studies are discussed, as well as the definition and function of the environment in the political science twin studies. The premature attempts to associate political traits with specific genes despite countertrends in genetics are also examined. I conclude by proposing that the alternative explanation of this article may explain certain puzzles in behavioral genetics, particularly why social and political traits have higher heritability estimates than common physical and medical traits. I map the main point of disagreements with the methodology and the interpretation of its results, and delineate the main operative implications for future research.

Both papers in this volume on which I was asked to comment (James E. Monogan III, “A Case for Registering Studies of Political Outcomes: An Application in the 2010 House Elections” and Macartan Humphreys, Raul Sanchez de la Sierra, and Peter van der Windt, “Fishing, Commitment, and Communication: A Proposal for Comprehensive Nonbinding Research Registration”) advocate registration regimes for our discipline. The recommendations in both are incremental [promoting, as Lindblom (1965) might have said it, the “intelligence of research” and cognizant of the costs in scientific learning from such a regime if rigidly enforced. Moreover, both papers cite studies by Gerber and various co-authors (e.g., Gerber, Green, and Nickerson 2001) demonstrating publication bias in political science, incentivizing researchers to manipulate their regression models until they can show a z-statistic ≥ 1.96, and thereby reaching standard levels of significance. I fully accept that Gerber et al.'s papers have detected a serious flaw in our scientific practices; there is a problem to be solved. The Monogan and Humphreys et al. proposals are therefore worthy of consideration.