Is Human Systems Integration Different from Human Factors Engineering?

DoD acquisition policy requires Human Systems Integration (HSI). Various human-centered engineering approaches are also gaining traction outside of military projects. But is HSI just a fancier way of saying Human Factors Engineering (HFE)?

You’d be forgiven for thinking as much. People unfamiliar with HSI or HFE see “human” and assume that the terms are synonymous. The result is programs renaming their HFE effort as HSI in order to keep up with the latest trends, but falling short of actually delivering the value of an integrated human engineering effort.

The best way to describe the difference is a good ol’ fashion, SAT-style analogy:

Human factors engineering is to human systems integration as mechanical engineering is to systems engineering.

At a high level, systems engineers coordinate the other engineering teams, ensuring that requirements are flowed down, interfaces are agreed upon, tradeoffs are made analytically, and the various components come together to form an integrated system. Design and development of specific components is conducted by those relevant engineering disciplines (mechanical, electrical, materials, software etc., etc.). The systems engineer doesn’t need to know how to design any particular piece of the system, just how all of the efforts interrelate to result in a complete solution.

In the same way, the human systems integrator coordinates the HSI domains, ensuring that system requirements are flowed down, specialists are appropriately involved in design decisions, tradeoffs are made analytically, and the integrated system fully considers the human components. The hands-on work of human factors, safety, survivability, etc. are conducted by the relevant expert, the integrator just needs to know how they all interrelate to result in a complete solution.

As you can see, the human factors engineer is much more akin to the mechanical engineer while the human systems integrator is much more akin to the systems engineer.

The difference between HSI and HFE

HFE designs and analyzes the human interfaces to the system using a variety of tools and methods appropriate to the project. Human factors engineers work closely with the teams designing system components to ensure that those components meet all HFE designs and requirements.

HSI is part of the systems engineering team and participates in all of the normal systems engineering activities (requirements decomposition, tradeoff analyses, integration, etc.) with special emphasis on the human-related disciplines1. HSI supports these disciplines in two ways: First, coordinating their efforts to maximize their synergies2 and reduce duplication of effort. Second, ensuring that the disciplines are given appropriate weight throughout the engineering process.

All of the HSI domains including HFE take into account the system requirements, mission need, intended user population, operational context, and human performance models to ensure that the system is operationally effective.

Clear as mud? Anything to add or quibble with? The comment section awaits!


  1. Manpower and personnel planning, training, human factors engineering, human survivability, habitability, environment, safety, and occupational health
  2. Sorry for the buzzword, but it’s the best term to use here