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What is the Nomological Net?

The nomological network is an idea that was developed by Lee Cronbach and Paul Meehl in 1955 (Cronbach, L. and Meehl, P. (1955). Construct validity in psychological tests, Psychological Bulletin, 52, 4, 281-302.) as part of the American Psychological Association's efforts to develop standards for psychological testing. The term "nomological" is derived from Greek and means "lawful", so the nomological network can be thought of as the "lawful network." The nomological network was Cronbach and Meehl's view of construct validity. That is, in order to provide evidence that your measure has construct validity, Cronbach and Meehl argued that you had to develop a nomological network for your measure. This network would include the theoretical framework for what you are trying to measure, an empirical framework for how you are going to measure it, and specification of the linkages among and between these two frameworks.

The nomological network is founded on a number of principles that guide the researcher when trying to establish construct validity. They are:

  • Scientifically, to make clear what something is or means, so that laws can be set forth in which that something occurs.
  • The laws in a nomological network may relate:
    • observable properties or quantities to each other
    • different theoretical constructs to each other
    • theoretical constructs to observables
  • At least some of the laws in the network must involve observables.
  • "Learning more about" a theoretical construct is a matter of elaborating the nomological network in which it occurs or of increasing the definiteness of its components.
  • The basic rule for adding a new construct or relation to a theory is that it must generate laws (nomologicals) confirmed by observation or reduce the number of nomologicals required to predict some observables.
  • Operations which are qualitatively different "overlap" or "measure the same thing" if their positions in the nomological net tie them to the same construct variable.

What Cronbach and Meehl were trying to do is to link the conceptual/theoretical realm with the observable one, because this is the central concern of construct validity. While the nomological network idea may work as a philosophical foundation for construct validity, it does not provide a practical and usable methodology for actually assessing construct validity. The next phase in the evolution of the idea of construct validity -- the development of the multitrait-multimethod matrix -- moved us a bit further toward a methodological approach to construct validity.

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