Fred W. Riggs, a prominent scholar in comparative public administration, significantly contributed to the field by advocating an 'ecological approach' – studying public administration in relation to its socio-economic, political, and cultural environment. In his analysis of the evolution of comparative public administration, Riggs identified three distinct trends that characterized its development:

1. From Normative to Empirical: Initially, the study of public administration, particularly in its comparative aspects, was largely normative. Scholars focused on prescribing how administration should function, often based on Western models, and sought to identify universal principles of good governance. Riggs observed a shift towards an empirical approach, where the focus moved to understanding how administrative systems actually operate in different contexts. This trend emphasized objective observation, data collection, and analysis of real-world administrative phenomena, rather than just prescribing ideals. It sought to describe and explain administrative behavior as it is, acknowledging the diversity of administrative realities.

2. From Ideographic to Nomothetic: The early comparative studies tended to be 'ideographic,' meaning they focused on describing unique cases or specific administrative systems in isolation. Each country or system was treated as a distinct entity, with little attempt to generalize findings across different contexts. Riggs noted a trend towards a 'nomothetic' approach, which aims to develop generalizable theories, concepts, and models that can explain administrative phenomena across a range of societies. This involved moving beyond mere description to seeking patterns, regularities, and causal relationships that could lead to broader theoretical frameworks applicable to multiple administrative systems, such as his own fused-prismatic-diffracted model.

3. From Non-ecological to Ecological: Perhaps the most significant trend identified by Riggs was the shift from a non-ecological to an ecological perspective. Earlier studies often viewed public administration as an isolated system, separate from its societal context. They focused on internal organizational structures and processes without adequately considering the external environment's influence. Riggs championed the ecological approach, which emphasizes the intricate interdependence between administrative systems and their surrounding environment – including social, economic, political, and cultural factors. This trend highlighted that administrative structures and behaviors are shaped by, and in turn shape, their environment, making it crucial to study administration within its broader societal context to understand its functioning and effectiveness.

These three trends collectively marked a maturation of comparative public administration, moving it from a prescriptive and isolated discipline to a more scientific, analytical, and context-sensitive field of study. Riggs's observations and his own theoretical contributions were instrumental in shaping this evolution, laying the groundwork for a more rigorous and comprehensive understanding of administrative systems worldwide.