From Multiple Streams to Muddling Through: Policy Process Theories and “Field of Vision”

Abstract Contemporary policy process theories are used to explain important aspects of the policy process, including the emergence or change of policies over time. However, these theories vary notably in their composition, such as their scope of analytical space, key concepts and assumptions, models of individual decision-making, and relationships between process-relevant factors and actors. There is little guidance on which theory may be best suited for explaining particular policy outcomes or how the different elements of the theories influence their analytical power. To begin to address this gap in the literature, a comparative analysis applied four established policy process theories to explain the emergence of the same policy outcome, a set of environmental policies associated with the North American Free Trade Agreement, while varying the analytical space or “field of vision” spatially and temporally. Overall, each theory demonstrated strong explanatory power but within analytical spaces of different scales, which indicates that the dimensionality aspects aspects the analytical space of policy process theories may contribute to a convergence in shared knowledge.


Introduction
Why do particular public policies emerge at particular times to address particular policy problems and not at other times? This question has driven much research in the field of public policy and led to the development of numerous theories1 to explain important aspects of the policy process, including the emergence or change of policies over time. Each contending theory constitutes a unique lens for understanding the policy process, with its own set of simplifying presupposition and critical relationships of concepts and propositions (Sabatier, 1999). As such, the models have varying levels of explanatory power for particular policies but there is little guidance to determine which theory may be best suited to explain a particular policy outcome. In other words, which policy process theory should be used?
According to Schlager (1999; see also Weible, 2017), no single theory can explain all policy outcomes and each one has its own strengths and weaknesses. In general, each theory seeks to explain why a particular policy emerges or changes within a given policy domain or space. To apply each theory, an analyst typically examines the processrelevant actors and factors that give rise to the policy change vis-à-vis the policy status quo within a specific analytical policy space or domain. Thus, defining the analytical space or scope of analysis is central to analyzing policy change, as the space simultaneously determines the actors and factors that will be considered in the analysis and the relationships between the two. However, defining the scope or boundaries of a policy domain or analytical space can be highly subjective (Birkland, 2011).
Given the important role that the policy domain or analytical space plays in policy process theories, it is surprising that specifying the boundaries and scope of a domain has received little scrutiny within the literature.2 To begin to address this gap in the literature, this research presents a comparative analysis of several contemporary policy process models to explore the relevance of scope of the policy domain or analytical space, referred to herein as the "field of vision", for analyzing policy emergence. The field of vision is adjusted spatially and temporally as each theory is used to explain the emergence of the suite of environmental policies developed for the North American Free Trade Agreement (NAFTA). Overall, the analysis highlights that different policy process theories have comparable explanatory power for the same public policies as the field of vision is varied across the theories.

Review of Literature on Policy Process Models
Researchers have been studying the policymaking process since the 1950s and have developed numerous policy process theories to understand the different process-relevant actors, factors, and dynamics that lead to either policy stability or change over time (see e.g. Sabatier, 1999Sabatier, , 2007Weible & Sabatier 2017). The body of literature associated with these theories is extensive and a thorough review is neither feasible nor necessary for setting the context for the analysis that will follow. Rather, the following review draws selectively from the corpus of policy process research. In general, existing policy process research has identified the process-relevant theoretical elements and factors that need to be considered in analyzing policy emergence and change. Heikkila and Cairney (2017) provide a general comparison of several contemporary policy process theories, including the punctuated equilibrium theory, multiple streams framework, narrative policy framework, and advocacy coalition framework, amongst others, to identify their respective frames of reference, foci, and concepts, along with their strengths and weaknesses and similarities and differences in explanatory outcomes. Their comparison highlights the key process-relevant elements and factors for each theory, including the actors, institutions, networks or subsystems, ideas or beliefs, policy context, and events, as well as the interactions between them (Heikkila & Cairney 2017: 303). In addition, the comparison identifies the scope and level of analysis and assumptions associated with each theory (Heikkila & Cairney 2017: 303). Taken altogether, this comparison underscores the variation in perspectives and approaches that can be brought to bear in analyzing the policy process and policy emergence.
Focusing specifically on the policy domain or analytical space associated with each policy process model, the scope of the analyses varies considerably and includes individual policy choices, political system stability, policy and politics interactions, advocacy coalition dynamics, collective choices in designing institutions, and dynamics of policy social construction (Heikkila & Cairney 2017: 306). The level of analyses also varies and includes individual actor, coalition, policy subsystem, action situation, entire policymaking system, and society (Heikkila & Cairney 2017: 306). The wide variability in specificity and foci of the analytical spaces for these theories undoubtedly underscores the fact that the "context of a policy theory field … is not conducive to systematic comparison" (Heikkila & Cairney 2017: 301).
Although it may be difficult to directly compare the form and structure of the policy process theories, that does not preclude using these theories in a comparative analysis of a single policy change. In general, the purpose of the research presented below is not to compare the theories per se, but rather how their analytical space varies in explaining a particular policy outcome. In doing so, this analysis will hopefully provide some insights into importance of the analytical spaces across the policy process theories as each is used to explain policy change while holding the particular policy outcome constant. The policy change to be examined is the emergence of a suite of environmental policies associated with NAFTA and the policy process theories used to explain the change are the punctuated equilibrium theory, multiple streams framework, advocacy coalition framework, and incrementalism. Each policy model is described in more detail below, but to first set the substantive policy context for the analysis, background on the environmental policies for NAFTA is provided.

Background on NAFTA Environmental Policies
The focus of this comparative analysis is on the emergence of a suite of trilateral environmental policies to address the potential negative environmental effects of NAFTA in the early 1990s. This suite of policies is frequently analyzed together because they are all associated with a single trade agreement, even though they may be located in different legal instruments and focused on addressing different negative environmental effects. A few of the environmental policies are located within core text of NAFTA while the majority of policies are set forth in the North American Agreement on Environmental Cooperation (NAAEC), a trilateral agreement negotiated between the U.S., Mexico, and Canada.3 Prior to NAFTA, the environmental effects of trade liberalization had not been directly considered during trade policy negotiations and the development of these environmental policies, and in particular the NAAEC, was considered a watershed event because these policies were the first to explicitly address the complex linkages between environmental protection and liberalized trade.
In general, trade liberalization can give rise to various negative environmental effects, which are often classified as legal, sectoral, product, and scale effects; for NAFTA, the principle effects of concern were the legal effects, in particular, the differing levels of domestic environmental safeguards or enforcement between trading partners, or a 'conflict of rules' between trade regime rules and domestic or international environmental laws (OECD, 1994;Nordström & Vaughan, 1999;Salzman 2001). Differing levels of safeguards or enforcement may foster a downward harmonization of regulations, or migration of dirty industries to countries with lower standards or enforcement (Cole, 1999;Nordström & Vaughan, 1999;Ferrantino, 1997) whereas a conflict between trade regime rules and environmental laws may restrict the use of trade-related measures for enforcement of international environmental laws and treaties or restrict domestic environmental regulations if the regulations are determined to be non-tariff barriers to trade (Nordström & Vaughan, 1999;Krutilla, 1997).
Overall, NAAEC established a trilateral commission, the North American Commission for Environmental Cooperation (CEC), responsible for implementing broad mandates to promote environmental cooperation and integration of trade and environment objectives under NAFTA, and improve enforcement of environmental laws in North America. Many of the environmental policies were considered innovative, including the public submission process, the state-to-state dispute resolution process, and NAFTA provisions related to privileging the trade-related measures under multilateral environmental agreements over obligations under the trade agreement and a commitment to not waive or otherwise derogate from domestic environmental measures in order to retain or attract investment (Allen, 2018). Collectively, the NAFTA environmental policies were intended to ensure that trade liberalization did not foster increased environmental degradation in North America, but particularly in Mexico.

Comparative Analysis of Policy Process Models
The emergence of the NAFTA environmental policies is examined using four policy process theories: punctuated equilibrium theory, multiple streams framework, advocacy coalition framework, and incrementalism. The first three theories listed were selected because of they are considered to be some of the most established theories in the policy field (Weible, 2017: 1) whereas the fourth theory, incrementalism or the science of muddling through, was also selected for this analysis because it is one of the longest standing policy process theories, widely known albeit eclipsed by more recent theories (Birkland 2011: 256). Incrementalism offers the broadest analytical space for analyzing policy change. Each of these theories is described in general first, followed by its application to explaining the emergence of the NAFTA environmental policies. Conceptually, the theories are presented in an order that starts with the narrowest spatial and temporal field of vision or analytical space and proceeds up to the broadest field of vision.
Punctuated Equilibrium Theory. The punctuated equilibrium theory developed by Baumgartner and Jones (1993) represents a policymaking process "characterized by long periods of incremental change punctuated by brief periods of major change" (Sabatier, 1999: 9); it can explain both policy stasis and dramatic change in policies, referred to as policy punctuations (Baumgartner, Jones, & Mortensen, 2014: 60). The dynamic at the center of this theory is the changing definitions of policy issues and agenda setting that allow for challenges to existing policies, which in turn open up opportunities for policy reversals (Baumgartner, Jones, & Mortensen, 2014: 60). This dynamic occurs because of the overlap and interaction between the politics of issue-specific policy subsystem(s) and the macro-politics of the Congress and presidency (for national level policies in the U.S.) (Baumgartner, Jones, & Mortensen, 2014: 61). Established policy subsystems, which support policy stasis, can be transformed when external actors redefine the policy issue and force changes to the subsystem, resulting in new policies (Baumgartner, Jones, & Mortensen, 2014: 64).
Prima facie, the application of the punctuated equilibrium theory appears to be particularly well-suited for explaining the emergence of the NAFTA environmental policies. Much of the literature on the NAFTA environmental policies describes these policies as groundbreaking, a drastic departure from past trade agreements (see e.g., Audley, 1997). Conceptually, it is hard to argue with this characterization given that trade agreements prior to NAFTA never included any environmental policies, so obviously, the inclusion of environmental policies under NAFTA can be viewed as a policy punctuation. However, in addition to this intuitive observation, a more detailed analysis reveals that emergence of these environmental policies can be explained by the transformation of then the dominant policy subsystem for trade policy and its interaction with the macro-politics of national-level political institutions. This transformation was driven by external actors, in particular environmentalists, who identified possible linkages between trade liberalization and on-the-ground environmental degradation and thereby crafted a different policy image for trade liberalization. These actors then sought to drastically modify the status quo trade policies as the NAFTA was being considered on the macro-political agenda.
Prior to NAFTA, there existed a policy monopoly for trade policy. Throughout the post-World War II era, the U.S. had been the primary advocate for trade liberalization and historically led efforts to negotiate trade agreements at the multilateral level under the General Agreement on Tariffs and Trade (GATT) framework (USITC, 2009). During this time period, there was a well-established policy monopoly for trade policy subsystem in the U.S., comprised of powerful producer interest groups (export-oriented) and a small number of political actors (e.g. pro-free trade congressmen, congressional trade committees) and bureaucratic actors (e.g. U.S. Trade Representative, Department of Commerce) closely aligned with the producer interest groups (Destler & Balint, 2000). These free trade advocates were united by a common goal to reduce barriers to trade and negotiated free trade agreements in relative secrecy while being weary of external actors seeking to impose new restrictions on trade (Esty, 1994;Audley, 1997).
Historically, environmentalists did not have a formal role in trade policy subsystem and the trade community did not consider environmental issues explicitly within free trade agreements (Esty, 1993;Audley, 1997). However, weak enforcement of environmental laws in Mexico coupled with an adverse ruling by the GATT (Christensen, 1991) while NAFTA was being negotiated provided environmentalists with sufficient evidence to argue that trade liberalization would adversely affect the environment. By recasting the policy image of trade liberalization as having extensive and dire environmental consequences, the environmentalists upset the trade policy monopoly and gained access to the trade policy subsystem in the U.S. (see Audley, 1997). The inclusion of environmentalists in this subsystem, in turn, resulted in the participation of other closely aligned political (e.g. congressional environment committees, proenvironment / pro-trade congressmen) and bureaucratic (e.g. U.S. Environmental Protection Agency) actors, which significantly transformed the trade policy subsystem. This recasting of the trade policy image ultimately resulted in the inclusion of environmental policies in NAFTA, a policy punctuation given the status quo of the trade policy subsystem prior to that trade agreement.
Multiple Streams Framework. The multiple streams framework, a policy process theory developed by Kingdon (1984) that built upon earlier work by Cohen, March, and Olsen, explains policy emergence as a somewhat stochastic event, when three separate streams of policies, problems, and politics within the policy process come together at opportune times to generate a policy change (Zahariadis, 2014). The problems stream consists of the nature of the policy problem, the policies stream constitutes the potential ideas that could be advanced as solutions, and the politics stream encompasses the prevailing politics and public opinion of the day (Zahariadis, 2014). These streams exist concurrently and independently of each other, but can come together during a window of opportunity to generate a new policy, triggered by a change in one or more of the streams and facilitated by policy entrepreneurs (Zahariadis, 2014).
The multiple streams framework also appears to be well-suited to explaining the emergence of the NAFTA environmental policies. However, unlike the punctuated equilibrium theory that when applied can explain changes to the trade policy domain, the multiple streams framework is used to explain changes to regional environmental policy domain, which is the primary focus of the NAFTA environmental policies. In general, the U.S., Mexico, and Canada have long recognized their ecological interdependence due to shared ecosystems on the North American continent (see e.g., CEC, 1997) and have established formal and informal environmental institutions at the national and subnationallevels to promote environmental policy coordination between the countries (see e.g., Munton & Kirton, 1994;Munton & Kirton, 1995).
At the national-level, the three countries have established numerous bilateral, and to a lesser extent, trilateral environmental institutions to facilitate joint action on environmental issues of common concern (see e.g. Munton & Kirton, 1994;Sanchez-Rodriguez, et al., 1998;Szekely, 1993). At the bilateral-level, examples include the International Boundary and Water Commission and International Joint Commission for managing transboundary waterbodies on the U.S-Mexico and U.S.-Canada borders, respectively. At the subnational-level, considerable environmental policy coordination has also occurred; by the early 1990s, there existed over 100 agreements related to environmental and natural resource issues between provinces and states in the three countries, of which about two-thirds were formal agreements (Munton & Kirton, 1995). Despite this rich network of subnational and national-level environmental policies covering all or part of the North American continent, overall environmental management for North America was highly fragmented (Sanchez-Rodriguez, et al., 1998). One observer noted that given "the leadership role that the three countries have traditionally played in international affairs …. it [is] rather surprising that the North American countries have not formally banded together to adequately care for their substantial corner of the earth…" (Szekely, 1993: 557).
By the early 1990s, some environmental policy advocates recognized the need for additional institutions to address unresolved or emerging environmental problems at the continental-level (see e.g. Kelly, 1998;von Moltke, 1993;Sanchez-Rodriguez, et al., 1998). As such, the policy idea for a trilateral environmental policy to promote broad-based regional environmental cooperation existed prior to NAFTA, although it was not given serious consideration within the regional environmental policy domain. When environmental concerns emerged during the NAFTA negotiations, environmentalists first proposed establishment of a trilateral institution to facilitate environmental policy coordination and cooperation between the three countries in 1991 and repeatedly raised the idea throughout the negotiations of NAFTA (see e.g., ATI, et al., 1991;NAS, et al., 1991;NWF, 1992;NRDC, et al., 1992;Kelly, 1993). At the same time, the environmental agencies in the three countries came to view establishment of a trilateral institution as an opportunity to advance their domestic environmental objectives and agenda and improve environmental management and cooperation at the regional level, and collectively supported the establishment of a credible and functional environmental institution (Allen, 2005).
As the NAFTA negotiations proceeded, environmental concerns gained more prominence at the nationallevel, especially after an adverse ruling by the GATT related to U.S. laws to protect dolphins (Christensen, 1991). Environmentalists used the ruling, along with general concerns about increased environmental degradation due to trade liberalization, to mobilize public opinion in support of environmental safeguards within NAFTA (ITR, 1992a(ITR, , 1992bInside U.S. Trade, 1993). This notable shift in public opinion, coupled with the efforts of environmentalists acting as policy entrepreneurs (Audley, 1997;Hogenboom, 1998), ultimately resulted in negotiation of a suite of trilateral environmental policies for NAFTA, including establishment of a trilateral environmental commission, the CEC, responsible for promoting broad-based environmental cooperation between the three NAFTA countries. In general, the changes in public opinion related to the need for environmental safeguards during negotiation of NAFTA created a window of opportunity, that when coupled with a pre-existing policy solution for improving regional environmental management in North America and policy entrepreneurs strategically advancing the solution within the macro-political arena, resulted in the emergence of new regional environmental policies that had been envisioned long before NAFTA existed.
Advocacy Coalition Framework. The advocacy coalition framework, developed by Sabatier (1988;& Jenkins-Smith, 1993), explains policy emergence and change through the functioning of policy subsystems. Policy subsystems are "defined by a policy topic, territorial scope, and the actors directly or indirectly influencing policy subsystems affairs" (Jenkins-Smith, et al., 2014: 189). These actors are aggregated "into one or more coalitions" which are based on shared beliefs and coordination strategies (Jenkins-Smith, et al., 2014: 191). These coalitions pursue different strategies to influence decision-makers and ultimately policy outcomes (Jenkins-Smith, et al., 2014: 193). Similar to the punctuated equilibrium theory, the advocacy coalition framework can be used to explain periods of policy stability as well as dramatic and non-incremental policy change (Jenkins-Smith, et al., 2014: 201). Major policy changes reflect a change in the direction or goals of a subsystem while minor policy changes are changes in secondary aspects of the subsystem (e.g. means for achieving the goals) (Jenkins-Smith, et al., 2014: 201). Major policy change may occur due to several dynamics that effect the subsystem, including the presence of some external event or shock that is outside the control of the subsystem participants, such as changes in public opinion or other policy subsystems, or when warring coalitions are forced to negotiate an agreement under certain conditions, such as a hurting stalemate that gives rise to an unacceptable status quo (Jenkins-Smith, et al., 2014: 202).
With its focus on policy subsystems, the advocacy coalition framework lends itself well to explaining the emergence of the environmental policies for NAFTA, with the analysis focused on the trade policy subsystem. As was noted above under punctuated equilibrium theory, trade policy in the U.S. had long been developed within a stable policy subsystem dominated by a coalition of industry representatives, pro-trade bureaucrats, and pro-trade legislators. This coalition held strong beliefs that freer trade benefited not just certain industries but all of society because of increased economic efficiency. However, starting in the 1970s and 1980s, this view began to change as increased trade liberalization and foreign competition contributed to the de-industrialization and economic devastation in the U.S. (Aaronson, 2001). At the same time, trade policy increasingly touched on non-tariff barriers to trade and efforts to reduce these barriers threatened the long-standing social compact in the U.S. (Aaronson, 2001). Trade policy could be used to restrict the setting of domestic social policies, such as public health, environmental, or labor standards (Destler & Balint, 2000) while disparities between countries' social policies could also create pressure for downward harmonization in order for domestic industries to remain competitive (Destler, 1991).
In general, these social costs of trade liberalization came to fore during the late 1980s and early 1990s, coinciding with the negotiation of NAFTA. Various coalitions formed to minimize these costs and protect their interests, such as labor, human rights, and environmental interests, within the trade policy domain (see generally, Aaronson, 2001). These coalitions likewise held strong beliefs related to the need to ensure fair labor practices, uphold human rights, and protect the environment. Initially, these social movement coalitions held little sway within the trade policy subsystem, but their ability to mobilize public opinion and align with key legislators in the U.S. Congress created the political imperative that their policy concerns be addressed as a condition for passage of NAFTA. As a result of this imperative, the environmentalists formed an increasingly powerful coalition within the trade policy subsystem and the competing beliefs and interests of the trade and environmental coalitions necessitated a negotiated agreement, which resulted in the environmental policies for NAFTA. Although these policies did not materially change the substantive terms of NAFTA itself, the policies reflect changes to the goals and direction of the trade policy subsystem, which have become firmly embedded within the subsystem and continue to this day.
Incrementalism. Developed by Lindblom (1959Lindblom ( , 1979, incrementalism is one of the earliest and widely known policy process theories; this theory posits that the bounded rationality of decision-makers (also assumed for other theories) constrains their ability to make drastic shifts in policy. As such, policies are changed incrementally, based on feedback from policy learning, giving rise to a series of small policy adjustments over time. This theory has been criticized as providing an incomplete explanation of policymaking (Baumgartner, Jones, & Mortensen, 2014: 69), but the theory is retained for this analysis because of its prominence within the policy field and the fact that it provides the longest and widest perspective on policymaking to understand how policies are tweaked at the margins and slowly evolve over time. Expanding the policy domain to the broadest possible context of environmental policymaking, in terms of both time and policy space, it considers the NAFTA environmental polices within the overall domain of international environmental policies.
The contemporary field of environmental policymaking is widely considered to have emerged in the 1960s as societal awareness about humans' impacts on the environment dramatically increased. This increased awareness fostered the passage of major environmental legislation within the U.S. and other developed countries. The U.S., for example, passed the National Environmental Policy Act in 1969, followed by major revisions to the federal Clean Air Act in 1970 and Clean Water Act in 1972. Since that time, there has been a proliferation of domestic environmental policies enacted by countries throughout the world. At the international-level, similar policymaking efforts were pursued to address transboundary or global environmental issues starting in the early 1970s. These efforts were initiated by the 1972 UN Conference on the Human Environment, which set into place a framework for coordinating "environmental policies throughout the international institutional system" (Young 2002: 34). Since the early 1970s, there has likewise been a proliferation of international environmental policies; at present, there are over 4,000 international environmental agreements, protocols, and the like (Mitchell, 2020), which collectively serve to create a global environmental governance system (IISD, 2006). These agreements are often focused on protecting specific natural resources and global commons or addressing particular global environmental problems.
In conjunction with the formal multilateral agreements and institutions within the international environmental policy domain, there have also been a multitude of other environmental policies developed since the early 1970s related to global economic development activities (Young, 2002: 35). These policies are not typically formal state-tostate international agreements but rather are policies adopted by specific development and financing institutions to mitigate the environmental impacts of their core activities, such as multilateral development and financing assistance, official development assistance, international trade, and foreign direct investment. In general, many of these policies were based on existing policies in the domestic policy arenas, such as completing environmental impact assessments of projects (see e.g. World Bank, 1972Bank, , 1974Bank, , 1995Bank, , 1997Wenning, 1985;Rich, 1985;Mendez & Houghton, 2020). These domestic policies were transferred to new policy settings and adjusted to fit the new context through a process of policy learning.
Multilateral financing institutions and official development assistance were the initial foci for this policymaking due to the tangible and extensive environmental impacts of their financing and development actions (Stein & Johnson, 1979). For example, in 1977, the U.S. required that multilateral development banks consider the environmental impacts of their loans (International Financial Institutions Act 1977;Rich 1985), but even as early as 1970, institutions such as the World Bank had committed in principle to review its projects for their environmental impacts (Rich, 1985: 703). Policies were developed and institutionalized over time, such as in 1980 with the New York Declaration of Environmental Policies and Procedures Relating to Economic Development and Committee of International Development Institutions on the Environment by multilateral development banks (Rich, 1985). Similarly, policies were developed to require environmental reviews and consideration for official development assistance activities; in the U.S., these policies were put into place starting in the 1970s as well (Rich, 1985: 713;International Financial Institutions Act 1977). By the 1980s, environmental policies and requirements for environmental impact assessments of development assistance projects were being developed by other countries (Wenning, 1989) in accordance with guidelines and principles agreed to by many countries (OECD, 2009).
The next realm of global economic development to adopt policies was related to international trade. Concern over the environmental impacts of trade actually emerged in the early 1970s, when the GATT Council established a Working Group on Environmental Measures and International Trade (Ahn, 1999: 821). Although this Working Group remained dormant until 1991, efforts to incorporate environmental policies into international trade policy began in the mid-1980s, during negotiations of the Uruguay round of the GATT and the U.S.-Canada free trade agreement, as the potential environmental impacts of these agreements became apparent (Shrybman, 1988a(Shrybman, , 1988b(Shrybman, , 1990Swenarchuk, 1988: Ritchie, 1990Ferretti, Makuch, & Traynor, 1991;Arden-Clarke, 1991). The first trade agreement to explicitly incorporate environmental policies was NAFTA in 1993 and since that time, many other bilateral or regional trade agreements have likewise incorporated similar policies (see e.g., Jinnah & Lindsay, 2016: Laurens, et al., 2019OECD, 2007). At the multilateral level, the World Trade Organization has examined integrating environmental policies but not yet done so explicitly (Gabler, 2010;WTO, n.d.). The last realm of global economic development activities to adopt environmental policies and principles has been private foreign investment, first in the early 2000s, with the Equator Principles and more recently with the Principles for Responsible Banking (IFC, n.d. ;Kamijyo 2004;UNEP, n.d.) to minimize the impacts of this investment on the environment.
Overall, since the early 1970s, many countries and international institutions have been developing policies to address global environmental problems that require interstate coordination and cooperation. In addition, these countries and institutions have pursued policies to mitigate the environmental impacts of global economic development activities associated with multilateral development and financing assistance, official development assistance, international trade, and private foreign direct investment. When viewed over the long arc of history, the development of these later environmental policies has been incremental, gradually moving from one realm of global economic development to another as well as slowly diffusing throughout each individual realm through a process of policy learning. Situating the adoption of the environmental policies for NAFTA within the broader temporal and spatial analytical space of international environmental policy during the contemporary environmental policy era, it appears that the NAFTA policies are an incremental policy change. Moreover, the incremental development of these policies over time was influenced by policy learning, as policymakers transferred existing domestic environmental policies to the international level based on new understandings of the policy problems and possible solutions.

Discussion and Conclusions
A comparative analysis using four different policy process theories, punctuated equilibrium theory, multiple streams framework, advocacy coalition framework, and incrementalism, was completed to explain the emergence of a suite of environmental policies for NAFTA. Although the theories differed in terms of their conceptualization of the policy process as well as the causal relationships between the process-relevant factors and actors, each was used to explain the same exact policy change in order to better understand one key dimension of the theories, the spatial and temporal scope of the analytical space or policy domain, referred to in this research as the field of vision, which varied across the theories. Spatially, the field of vision ranged from a fairly narrowly scoped trade policy subsystem for the punctuated equilibrium theory and advocacy coalition framework to moderately scoped regional environmental policy domain for the multiple streams framework to the broadly scoped global domain of international environmental policy for incrementalism. The field of vision also varied temporally, from a relatively short time period surrounding the development of the NAFTA environmental policies for the punctuated equilibrium theory and advocacy coalition framework to a much longer time period, from around 1970 to present, for incrementalism, although placing distinct temporal boundaries on the field of vision appeared to be a somewhat subjective undertaking. Overall, it appears that scope of the analytical space is central to the explanatory power of these policy process theories because the scope defines the boundaries for capturing different process-relevant factors, actors, and dynamics for a policy analysis. Both the spatial and temporal dimensions of the field of vision are important although the temporal scope has historically been more implicit than well-defined (Barke & Champlin Gurley, 2014).
Overall, the comparative analysis indicates that the four policy process models have strong explanatory power when applied to the emergence of the NAFTA environmental policies and adjusting the field of vision is key to that outcome, however, it is important to recognize that there is a lot of subjectivity associated with the defining the analytical space as well as other key concepts for these models that influence the analysis results. Policy domains, for example, are defined largely by the nature of the policy problem, which itself depends on the social construction of the problem, potential solutions, agenda, and groups involved (Birkland, 2011). In other words, domain boundaries are theoretical constructs that can be conceptualized and adjusted at will. Likewise with the concept of policy change and what constitutes a theoretically relevant change in policy. For the advocacy coalition framework, policy changes are categorized as minor or major depending on "the extent to which alterations deviate from previous policy" (Jenkins-Smith, et al., 2014: 201). However, defining a policy change may be directly linked to defining the scope of the policy domain, and Lindblom (1979) provides an illustrative example of this dilemma. When discussing examples of incrementalism, he highlights different policy changes, the first being changing a discount rate, the second changing the type of monetary control used by a country, the third, changing the type of monetary system used, and the last, changing the basis for economic exchange. How the policy domain is conceptualized, whether it is the entire economic system or merely one element in it, influences how each of these policy changes are perceived, in other words, where along the continuum of incremental to drastic the policy change may fall (Lindblom 1979). Clearly, there remains much work to be done in refining and building robust policy process models, and towards that end, the comparative research presented herein provides some insights into the importance of some dimensions of these models, in particular the field of vision or analytical space.

Conflicts of Interest:
The author declares that there is no conflict of interest.
Author Biography. Linda J. Allen is an independent researcher focusing on environmental policy issues. She received a PhD in public policy from Indiana University and has published extensively on issues related to trade and environment.