The Ties that Bind Us: The Influence of Perceived State Similarity on Policy Diffusion

• Date: 01 June 2021
• Published date: 01 June 2021
• DOI: 10.1177/1065912920906611
• Subject Matter: Articles

https://doi.org/10.1177/1065912920906611

Political Research Quarterly

2021, Vol. 74(2) 377 –387

© 2020 University of Utah

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DOI: 10.1177/1065912920906611

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Article

Since Walker’s (1969) article on policy diffusion, research

focusing on how policies spread across the United States

has often relied on a key assumption—geographic conti-

guity drives diffusion. Early diffusion literature argues

that policies spread more readily from state to state when

the states border each other or are in the same region

(Berry and Baybeck 2005; Gray 1973; Walker 1969).

Meta-analyses of the literature show that contiguity is

almost always included in diffusion models and is often a

predictor of policy adoption (Maggetti and Gilardi 2016).

Yet, there are plenty of examples of how contiguity

does not explain how policies travel across U.S. states.

The legalization of same-sex marriage is one example.

Massachusetts and Connecticut were the first two states

to legalize same-sex marriage in 2003 and 2008. Iowa,

however, halfway across the country, was the third

adopter in 2009. This is one of many examples of non-

contiguous policy adoption. Clearly, there is more at play

in how policies diffuse than just geographic proximity.

Recent research has challenged contiguity as a mea-

sure of diffusion and proposed alternative understandings

of policy adoption and innovation. Scholars are using

more sophisticated measures and methods to understand

diffusion beyond the role of contiguity (Desmarais,

Harden, and Boehmke 2015; Nicholson-Crotty and

Carley 2018; Pacheco 2012; Shipan and Volden 2012).

This more methodologically rigorous research has shown

that, while contiguity is relevant to understanding policy

diffusion, it is only a “good starting point” but is “overly

limiting” and “sometimes misleading (or even wrong)”

(Gilardi 2016). Despite this, scholars continue to include

contiguity as a one-size-fits-all variable in model

specification.

We propose using a new measure, perceived state

similarity, as a more sophisticated and versatile alterna-

tive to contiguity. In this study, we generate and use a

continuous measure of citizen perceptions of state simi-

larity to predict the diffusion of eighty-nine policies

adopted from 2012 to 2016. We find that perceived state

similarity is a strong predictor of dyadic policy similar-

ity. We also find that similarity remains a strong predic-

tor of diffusion when expanded to a larger set of policies

in a pooled event history analysis (EHA) from 1990 to

2016. We suggest scholars consider moving beyond

contiguity to understand relationships between states

when modeling policy adoption and innovation, and use

perceived state similarity as a way to understand inter-

state connections.

906611PRQXXX10.1177/1065912920906611Political Research QuarterlyBricker and LaCombe

research-article2020

1Warren Wilson College, Swannanoa, NC, USA

2The University of Iowa, Iowa City, USA

Corresponding Author:

Christine Bricker, Department of History & Political Science, Warren

Wilson College, 701 Warren Wilson Rd., Swannanoa, NC 28778,

USA.

Email: cbricker@warren-wilson.edu; christine-bricker.com

The Ties that Bind Us: The Influence

of Perceived State Similarity

on Policy Diffusion

Christine Bricker1 and Scott LaCombe2

Abstract

In this paper, we propose a new measure to understand policy connections between the states. For decades, diffusion

scholars have relied on the largely untested assumption that contiguous states are more similar than noncontiguous

states, despite evidence that similarity is more complex than geographic proximity. We use a unique survey of citizens’

perceptions of other states to construct a national network of similarity ties between the states. We apply this new

measure with a data set of state policy adoptions in a dyadic and monadic event history analysis and find that similar

state adoptions are a reliable predictor of policy innovation. We argue that perceived state similarity is a more

complete measure of how states look to each other than contiguity.

Keywords

diffusion, similarity, policy, state politics, event history