Trade studies

If you have worked as or with a systems engineer from the Defense and Aerospace industries, you have very likely heard the term “trade study” used to describe a type of design analysis and the white paper or report that documents it.  From my travels, engineers from other industries are more likely to call the same task a “design decision” or “design tradeoff“.

From a human thinking perspective all design is decision-making.  Whenever you stand in the present and seek to answer “Which one?” or “Which way?” you are making a decision.  A decision is a fundamental question/issue that demands an answer/solution.  Every trade study seeks to make (or at least partially inform) one decision or a cluster of related decisions.  Before you launch any trade study effort you should first specifically define the scope of the analysis.  To do so, state/frame the decision or decisions that you are attempting to make; this bounds the problem domain for which a best-fit solution will be sought.

There’s no magic or unique process for completing a trade study – you just follow the best thinking practices associated with any decision:

  • Define criteria
  • Define alternatives
  • Evaluate alternatives
  • Select/commit to a best-fit alternative for implementation

Of course, the supporting analyses that are used to inform the “Evaluate alternatives” step may vary widely depending on the decision scope.  You may be able to rely on paper analysis; simple estimates of the effectiveness of the alternatives based on your experience.  You may populate spreadsheets or use math models with lots of probabilities or run custom and complex simulations.  You may build and test a few prototypes or do field trials to better understand the alternatives’ performance.  As always, you should tailor the rigor of your analysis and completeness of your documentation to match the importance of each decision.

The Decision Driven® Solutions Framework (DDSF) is built to:

  • Support a rich trade study process, but with easy-to-use web tools (e.g. drag-drop weighting/scoring)
  • Accelerate it by providing proven decision patterns (well-framed decisions, ready-to-attack) and criteria patterns (~10 criteria per decision)
  • Provide rich graphics (Tornado Chart, Spider Chart) to foster and communicate insights
  • Generate a Decision Report that could be pasted into your company’s trade study document template.

I particularly like to use the Spider Chart when summarizing the trade space that the alternatives occupy.

Spider Charts highlight the trade space

Every viable alternative will create a web on the spider chart that falls between the Threshold for each criterion (at the center of the chart) and the Objective (best realistic achievable value).  The ideal alternative (which almost never exists) is shown by the outermost web outlined by the grey line on the chart.  Any real-world alternative will have its own strengths and weaknesses; selecting it will force you to trade-off design margin between the various factors.  The best-fit solution is the one with the maximum area; it offers the highest average design margin across all factors when the importance (weight) of each factor is considered.

You may also use a Tornado Chart to compare any pair of promising alternatives.  In the example below, the systems engineer will have to trade-off design margin in manufacturing cost, development cost and reliability in order to gain advantages in operating cost, hazard removal, strategic fit, etc.

Tornado Chart highlights design margin tradeoffs

Use the powerful capabilities of the Decision Driven® Solutions Framework (DDSF) to capture, visualize and communicate your trade studies. Start your free trial of DDSF by contacting the Decision Driven® Solutions team at trial@decisiondriven.com or solutions@decisiondriven.com.

About decisiondriven

Innovator in Decision Management, Systems Thinking and System Engineering methods and tools
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