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Heuristic Methods

Using Rules of Thumb

Most of us use "rules of thumb" in all sorts of areas of our daily lives. "When the needle on the fuel level indicator gets to the red, I know it'll last at least another 20 miles", for example, or "Software with a user interface that's anything other than grey or blue hardly ever gets through the user acceptance testing."

These rough rules, based on experience, are invaluable because they help us to make decisions without further detailed fact-finding: Drivers know they don't need to divert immediately to find a fuel station, and the software designer can save him or herself rework later by making the interface blue or grey in the first place.

But no one expects these rules to be 100% accurate: If the car ran out of fuel in 18 miles, the driver wouldn't be particularly surprised, and if testing showed that users actually liked an application that had a tasteful green interface, the developer might raise an eyebrow, but that would be all.

This is because rules of thumb are only used in situations where the risks associated with using a "good enough" approximation are acceptable. No one would use a rule of thumb such as this fuel usage one for a F1 racing car: They'd do a detailed analysis of the exact amount required to cover the race distance.

The formal term for these rules of thumb is "heuristics". Heuristics are a topic of interest in various fields from computer science to psychology and philosophy, but the principle is the same in all of these.

When to Use the Tool

Because a heuristic is a model which offers only a limited representation of reality, it should only be used when the speed or low cost of using it makes it better value than using a detailed set of data. So heuristics are often used in calculating estimates, for proof-of-concept prototypes, or for filtering a set of options so that you are left with a shortlist of a manageable size.

Constructing a Heuristic

Heuristics need to be formalized if they are to be most useful. This raises them above the level of "gut instinct", and it also means that they can be shared with other people.

When you find yourself using your experience to make a judgment, try to work out the rule of thumb that you've just invoked. If possible, add this to your procedure manual, or talk about it with a colleague so that your experience is validated and passed on.

A typical example in a car breakdown call centre might be, "25% of all reported breakdowns are caused by running out of fuel, so always start by asking the driver to check this before you schedule a mechanic."

In this case, using the heuristic allows a certain proportion of breakdowns to be "fixed" immediately, which means that the limited number of mechanics can focus on the real breakdowns.

Heuristics can also be created specifically to solve a problem. For example, creating a diagram or straw man showing a possible solution will help you identify where your basic idea doesn't work, or is lacking some important feature, so that you can refine it more easily.

Another heuristic approach is to take a solution to another problem, and adapt it to solve yours. TRIZ is a systematic and highly developed approach for doing this.

Heuristic Checklists

Whether heuristics are used to filter a large number of options down to a manageable number, or whether you want to make an early "go/no go" decision, you will usually need to draw up a checklist of heuristics, rather than simply use an individual rule of thumb.

For example, in the food industry, the following heuristics might help the product development team decide whether it's worth investing in taking a new pie to the test marketing stage:

• Does the pie look appetizing in its packaging?
  
• Can it be packaged so that it won't be damaged in transit?
  
• Can it be cooked in under 20 minutes, so that busy people will buy it?
  
• Is its shelf life at least 5 days from manufacture to "use by" date?
  
• Does it maintain its integrity when sliced (or will the pastry topping fall apart when being transferred to a plate)?

This type of list will have been developed based on experience of previous products, and from market research. Of course, there's no guarantee that a pie that meets all these criteria will prove to be a success: it might not taste as good as rival products, and so not attract repeat sales, or the mix of filling ingredients might make it too expensive. However, the heuristic checklist will help the development team quickly and cheaply weed out "non-starters".

Key Points

Heuristics or "rules of thumb" are models based on experience. When you use heuristic, it's important to remember that these models have their limitations, and so heuristics should not be applied in situations where there is a high degree of risk associated with making the wrong choice.

The term "heuristic methods" can be used to describe any problem solving or creativity technique that involves creating a basic model as a starting point for further experimentation or refinement. Heuristic methods are trial-and-error approaches.

Apply This to Your Life: Think of situations where you regularly apply your experience, in which you could formalize the rules of thumb that you use, and so save yourself or others time on future occasions. Possible areas could include: Filtering resumes for shortlisting, when recruiting for an in-demand job. Choosing suppliers. Homing in on the sources of a problem referred from customer services. Next time you have a problem to solve, consider building a heuristic model of a potential solution. See if this helps you evaluate whether your idea is worth working up into a complete solution, or whether it contains fundamental flaws that mean you need to start again.

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