1. 1
Valerie Niklas
Literature Review on Policy Diffusion
December 17, 2015
Abstract
The objective of this review is to clarify and organize what research has been done in
regards to policy diffusion, as well as how policy diffusion research can be improved. I found that
there were four major factors which influence policy diffusion: internal and external pressures,
learning, coercion, and policy characteristics. Based off of these factors, one of the strongest
conclusions we can draw from existing policy diffusion research is that policy diffusion is not a
concrete process. Policy adoption and diffusion revolves around a district, state, or nations
individual political, economic, and societal circumstances, as well as the characteristics of the
policies.
Introduction
Policy diffusion, defined as the phenomenon in which policy adoption is influenced by
policy choices made elsewhere, has been studied by political scientists for decades. Therefore,
continuing research in this field may be difficult without a strong understanding of what needs to
be researched and what has already been researched. This review found that existing research
points to four determining factors in policy diffusion: internal and external pressures, learning,
coercion, and policy characteristics. The first section will look at environmental policy, and how
internal and external pressures play a role in the diffusion of environmental policymaking. The
third discusses learning, and the three primary factors governments consider when adopting
policies from other governments: innovation, proximity and ideology, and political consequences.
The fourth section will assess how coercion by powerful players such as the media, government,
and stakeholders affects diffusion. The final section will summarize ways policy diffusion research
can be improved.
Internal vs. External Pressures
It is not surprising that states may prioritize adopting a policy when there is internal or
external pressure to do so. However, there might be limits to a nation or state's ability to adopt
policies. One field of study where this was applicable was environmental policymaking. Two
consistent findings were made in research revolving around environmental issues. First, that
economic factors and a national capacity for change were important factors. Second, that internal
and external pressures led to environmental policy change.
Kern et al. (2005) and Daley (2005) found in their research that economic resources of a
country or state played an important role in policy adoption and diffusion. A core finding of Kern
et al.’s (2005) research was that the national capacity for change was an important factor in which
policy’s are adopted. Governments must take into account economic resources, as well as political
or social barriers. For example, a policy which contradicts national traditions has less of a chance
of being implemented. Without the proper resources, a state might not be able to adopt the same
policies a wealthier and more powerful state might adopt. This would lead to the conclusion that

2. 2
internal factors can affect diffusion positively or negatively. The easier the policy can be
implemented without repercussions, the more likely it is to diffuse.
Matisoff (2008), Kern et al. (2005), and Daley (2005) all concluded that there were external
and internal pressures that affected policymaking. Matisoff (2008) found that internal demand for
a policy or solution played an important role. He found this by looking for the motivation behind
policy diffusion. However, motivation does not necessarily only come internally. External
pressures such as international agreements, or recovering from an environmental scandal can also
motivate players to bring environmental policies on the agenda. Their conclusions suggest that
policy diffusion, at least in terms of environmental policy, depends on international and national
demand. Moreover, if there is a crisis or pressure to act then policies are adopted. China might be
pressured externally because they are such a powerful industrialized player in the international
community, but it might also be pressured internally, by the populace, because of the smog
problem. These conclusions are especially applicable to environmental policy because there is a
global and local need for change, however research on charter school policy diffusion also found
that intrastate circumstances, such as political structures, the presence of formal organizations and
social movements, affected diffusion.
In sum, when there is a statewide, national, or international crisis or pressure to change,
diffusion is likely to occur if the government has the means to do so. These conclusions are drawn
from research that specifically target environmental policymaking, further research could be done
to assess the extent of these correlations.
Learning
An overwhelming amount of the research agglomerated for this review concluded that
states learn from states. However states do not simply turn to any other government. Researchers
found several different strategies states use when looking at other policies, specifically: innovation,
ideological similarities, and political consequences.
Innovation and Front-Runners
When looking at policy knowledge diffusion, that is the diffusion of ideas of policies rather
than the actual implementation of policies, researchers found that policy makers actively seek out
policies from more innovative states (Glick & Friedland, 2014). Innovative states were determined
through an "Innovativeness score", determined by Boehmke and Skinner (2012). When larger and
more influential countries adopt a policy, the diffusion process is much higher than if a smaller
country adopts the policy first (Kern et al., 2005). These front-runner countries, such as Britain,
the U.S., and Germany, were found to have a serious impact of environmental policy adoption
because they are seen as influential and innovative. Shipan and Volden (2008) found that a core
mechanism for diffusion was imitation of larger cities, which they found tended to be innovative
leaders. These conclusions mean that powerful and innovative governments influence policy
diffusion, and that states and nations turn to these players when looking for policies.
Proximity and Ideology

3. 3
Proximity and ideology have been linked together because most research conducted on
regional similarities of policies led to the conclusion that it was predominantly similar ideology
that affected the diffusion of these policies.
When researching charter school policy diffusion across the United States, Renzulli and
Roscigno (2005) found that there were regional similarities in charter school legislation. They
suggest that there are two main factors for this. First, information is most easily transferred through
shared borders. When states are uncertain, they will turn to neighboring states to evaluate whether
a policy is a success or not. Second, states turn to states with similar cultural norms, as well as
shared regional identities for policymaking. When looking at how states study each other, Glick
and Friedland (2014) discovered that states searched for policies in neighboring states, however
they found that similarity of states accounts for diffusion more than proximity. These conclusions
mean that although proximity does play a role in learning, states predominantly factor in and learn
from similar states. Gilardi (2010) found that ideological positions influence the interpretation of
policies and their effectiveness. Specifically that “Right governments tend to be more sensitive to
information on the electoral consequences of reforms, while left governments are more likely to
be influenced by their policy effects.” (Gilardi, p.660). Policy effects refers to the outcomes of the
policies, how effective or ineffective it was, what drawbacks it had, etc. This means that not only
do states turn to ideologically similar states, but their ideologies influence their views and
interpretations of policies.
Political Consequences
Perhaps most importantly but not unique from the previous strategies is that states factor
in political consequences and effectiveness when adopting policies. As previously stated, ideology
affects how governments view the effectiveness of a policy. Ideology is also taken into account
when asking whether a policy will work for the state (Nicholson-Crotty & Carley, 2015). States
cannot adopt policies without taking into account the political makeup of their constituencies.
Furthermore, governments must consider political consequences of policies (Gilardi, 2010). If they
were to adopt a policy that conflicts with internal politics, there could be backlash. In conclusion,
diffusion most frequently occurs after a state has investigated a policy and asked whether it would
be applicable to them.
Learning is one of the biggest contributors to policy diffusion. States will wait to see if a
policy is effective before adopting it. It is usually innovative players which are first to implement
these policies. Further research could be done to better understand the connection between learning
from policy and from political outcomes, and finding the connection between ideology and prior
beliefs.
Coercion

4. 4
Significant research points to coercion as a mechanism for policy diffusion. This review
will mention three of the most prominent players of coercion: the media, government players, and
stakeholders.
Media
In a review of 23 studies on the diffusion of criminal justice policies, Bergin (2015) found
that mechanisms such as geographic proximity and political ideology had mixed results, whereas
media attention had consistent support in increasing policy diffusion (2015). When studying the
effects of media attention on fetal homicide policies, Oakley (2009) found that increased media
attention increased the likelihood of policy change in states. Media attention makes a policy more
salient, which puts pressure on legislators, and changes public opinion.
Government Players
Another important player in policy diffusion is the government. Karch (2010) analyzed the
politics of embryonic stem cell research and found that the national government can influence state
agendas in several ways. National political activities (Supreme Court rulings, public opinion) can
affect the diffusion process, national governments can provide financial incentives and help states
overcome certain obstacles, and encourage agenda setting in states (Karch, 2010). Shipan and
Volden (2008) also found that vertical coercion by governments affected diffusion. They found
that it is very easy for national governments to coerce states to implement policies through the use
of grants.
Stakeholders
Finally, stakeholders and interest groups play an important role in policy diffusion.
Researchers looked at modification, or the process by which states alter statutes in response to
political and societal changes, to better understand the effect of stakeholders on diffusion. They
found that during this process, stakeholders are able to influence information that lawmakers need
to take into account (Karch & Cravens, 2014). In other words, this process gives the opportunity
for other parties to give new or biased information, therefore influencing the final statute. Garret
and Jansa (2015) looked at the influence of interest groups on policy diffusion and had similar
findings: special interest groups can influence the diffusion process by providing information to
lawmakers. They use model legislation and connections to legislators to influence state policy
making (Garret & Jansa, 2015). However, it is important to note that research on environmental
policymaking found that interest groups were not influential in decision making, suggesting that
this mechanism could be relative to areas of policymaking (Daley, 2005).
In sum, there seems to be a strong connection between powerful influences and policy
diffusion. Furthermore, Karch and Cravens (2014), who studied the process of modification to
better understand policy diffusion, concluded that there is much to be learned from treating
diffusion as a process, to better understand specific mechanisms which affect diffusion.
Policy Characteristics

5. 5
A final influence on policy diffusion is the characteristics of individual policies. Nicholson-
Crotty (2009) found that looking at policy characteristics can help formulate predictions about the
diffusion of certain policies. He found through a multivariate analysis that high-salience, low-
complexity policies were most likely to diffuse rapidly because lawmakers are willing to forgo
policy learning in order to have immediate electoral gains. Moreover, salience and complexity of
a policy were found to be the two key characteristics in policy diffusion. Salient policies are key
because a vast majority of people are concerned or affected by it, therefore there is increased
incentives for policymakers to take action. Salient policies therefore diffuse more rapidly.
Complex policies require expertise and technical information, which takes more time. Therefore
complex policies tend to increase uncertainty and diffuse more slowly (Nicholson-Crotty, 2009).
In terms of environmental policy diffusion, Kern et al. (2005) found that policies which called for
a redistribution of funds were controversial.
These findings make it clear that policy characteristics affect the rate of diffusion. Further
research could be done to investigate the effects of other policy characteristics.
Research Methods: What Can Be Improved?
With the amount of research on policy diffusion, there are critics on how policy diffusion
research is conducted. To conclude this review I will summarize the ways researchers suggest we
can improve policy diffusion research.
According to Gilardi (2015) there are four ways ways to improve policy diffusion research.
First, he suggests that instead of thinking of new ideas, researchers should focus on new
measurements of existing ideas. Second, researchers should decide whether they are hoping to
learn something new about diffusion, or to understand more of a pre-existing phenomenon. Third,
researchers should develop new research designs tailored to their specific research question. He
suggests that they “use better data, carry out placebo tests whenever possible, and pay more
attention to causal inference.” (Gilardi, p.9). Fourth, he says researchers must make it clear why
their conclusions matter.
Dobbin et al. (2007) argue that theorists often attribute identical phenomena to different
mechanisms. These overlaps can be seen in some of the research shown here. He devises four
schools of thought of policy diffusion: constructivism, coercion theorists, competition theorists,
and learning theorists. He says that there are overlaps in these theories and that much can be learned
from looking at the big picture, “Scholars who have devised strategies for testing the concrete
mechanisms that the four different schools point to have not only produced more rigorous and
compelling analyses, but they have also developed new insights that feed back into theory
development” (Dobbin et al., p. 464). This means that researchers should think outside what their
individual theories point to, and try to understand how other mechanisms might be at play.
Conclusion
This review determined that there are four primary groupings of existing policy diffusion
research. First, when there is an internal or external demand for change or intervention, diffusion
of these policies occurs more rapidly, if the policies are financially and politically realistic for a
government. Second, governments learn from existing policies. They tend to learn from states that
are most innovative, with similar ideologies and close proximity. When implementing these

6. 6
policies, they tailor them to their individual circumstances. Third, coercion by the media,
government, and stakeholders helps diffusion occur more rapidly through financial, social, and
political incentives. Fourth, the characteristics of certain policies, especially salience and
complexity, affect how rapidly they will diffuse. Finally, future researchers should focus on what
we already know about policy diffusion and find ways to better understand existing phenomena.
References
Bergin, T. 'How And Why Do Criminal Justice Public Policies Spread Throughout U.S. States? A
Critical Review Of The Diffusion Literature'. Criminal Justice Policy Review 22.4
(2011): 403-421. Web. 21 Oct. 2015.
Daley, D. M. 'Horizontal Diffusion, Vertical Diffusion, And Internal Pressure In State
Environmental Policymaking, 1989-1998'. American Politics Research 33.5 (2005):
615-644. Web.
Dobbin, Frank, Beth Simmons, and Geoffrey Garrett. 'The Global Diffusion Of Public Policies:
Social Construction, Coercion, Competition, Or Learning?'. Annu. Rev. Sociol. 33.1
(2007): 449-472. Web.
Garrett, K. N., and J. M. Jansa. 'Interest Group Influence In Policy Diffusion Networks'. State
Politics & Policy Quarterly 15.3 (2015): 387-417. Web.
Glick, D. M., and Z. Friedland. 'How Often Do States Study Each Other? Evidence Of Policy
Knowledge Diffusion'. American Politics Research 42.6 (2014): 956-985. Web.
Gilardi, F. 'Four Ways We Can Improve Policy Diffusion Research'. State Politics & Policy
Quarterly (2015): n. pag. Web.
Gilardi, Fabrizio. 'Who Learns From What In Policy Diffusion Processes?'. American Journal of
Political Science 54.3 (2010): 650-666. Web.
Karch, A., and M. Cravens. 'Rapid Diffusion And Policy Reform: The Adoption And
Modification Of Three Strikes Laws'. State Politics & Policy Quarterly 14.4 (2014):
461-491. Web.
Karch, A. 'Vertical Diffusion And The Policy-Making Process: The Politics Of Embryonic Stem
Cell Research'. Political Research Quarterly 65.1 (2010): 48-61. Web.
Kern, Kristine, Helge Jörgens, and Martin Jänicke. 'The Diffusion Of Environmental Policy
Innovations: A Contribution To The Globalisation Of Environmental Policy'. SSRN
Electronic Journal n. pag. Web.

7. 7
Matisoff, Daniel C. 'The Adoption Of State Climate Change Policies And Renewable Portfolio
Standards: Regional Diffusion Or Internal Determinants?'. Review of Policy Research
25.6 (2008): 527-546. Web.
Nicholson-Crotty, S., and S. Carley. 'Effectiveness, Implementation, And Policy Diffusion: Or
"Can We Make That Work For Us?"'. State Politics & Policy Quarterly (2015): n. pag.
Web.
Oakley, M. R. "Agenda Setting And State Policy Diffusion: The Effects Of Media Attention,
State Court Decisions, And Policy Learning On Fetal Killing Policy". Social Science
Quarterly 90.1 (2009): 164-178. Web.
Renzulli, L. A., and V. J. Roscigno. 'Charter School Policy, Implementation, And Diffusion
Across The United States'. Sociology of Education 78.4 (2005): 344-366. Web.
Shipan, Charles R., and Craig Volden. 'The Mechanisms Of Policy Diffusion'. American Journal
of Political Science 52.4 (2008): 840-857. Web.
VOLDEN, CRAIG, MICHAEL M. TING, and DANIEL P. CARPENTER. 'A Formal Model Of
Learning And Policy Diffusion'. Am. Pol. Sci. Rev. 102.03 (2008): n. pag. Web.
Yukawa, T., I. Yoshimoto, and S. Yamakage. 'International Policy Diffusion At The Systemic
Level: Linking Micro Patterns To Macro Dynamism'. Journal of Theoretical Politics 26.2
(2013): 177-196. Web