The Weird World, and Equally Weird Measurement Models: Reactive Indicators and the Validity Revolution

Abstract

Researchers using structural equation modeling (SEM) aspire to learn about the world by seeking models with causal specifications that match the causal forces extant in the world. This quest for a model matching existing worldly causal forces constitutes an ontology that orients, or perhaps reorients, thinking about measurement STRUCTURAL EQUATION MODELING, 14(2), validity. This article illustrates several ways the seemingly innocuous quest for structural equation models that mirror "the world beyond" confronts entrenched notions of measurement validity. The article begins by considering simple measurement models and ends by "discovering" a new class of indicators called reactive indicators. Reactive indicators act as both the cause and effect of an underlying latent variable. The identifiability of a simple model containing a reactive indicator is proven and a research example illustrating the use of a reactive indicator is provided. However, the real challenge is to understand how an indicator can be both a cause and effect of the latent it measures. The understanding does not come from complying with the traditional rules for reliability and validity, but from focusing on the quest to make the structural equation model match the structuring of the worldly forces we seek to understand. Valid measurement in the context of a weirdly structured world requires an equally weird structural equation model. SEM RESEARCH ONTOLOGYMost structural equation modeling (SEM) researchers do not doubt the existence of an underlying causally structured world. For them, the issue is not whether a causal world exists but which particular causal forces provided the data at their fingertips. The ontological commitment to seek the structure of an existing causal world is buttressed by multiple epistemological commitments concerning the most trustworthy methodological means via which researchers can come to know the extant world. The epistemological commitments include the methodological admonitions: to avoid contradictory causal claims, to seek logical implications of one's causal claims, to seek evidence relevant to those implications, and to be diligent in making observations that test one's causal understandings.This article does not pursue measurement and validity in the context of epistemology or methodological diligence (attentiveness to gathering and handling data). Nor does it pursue the philosophy of whether the world's causal structure is fundamental, or merely coincidentally parallel because it floats on some unfathomably deeper sea of "structures that produce causal structuring." Instead, the consequences of the research quest to supplant the current hazy and incomplete understanding of the worldly forces is pursued by locating, representing, and encapsulating the actual worldly causal forces within a structural equation model. The article examines the consequences of making an ontological commitment to the structured existence of underlying causal forces as producing the values of observed variables-namely the research co...

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