Fast-And-Frugal Trees In A Nutshell

Fast-and-frugal trees are classification trees with sequentially ordered cues that aid in decision making. Fast-and-frugal trees (FFTs) are very simple illustrations of heuristic decision making. Each tree is comprised of sequentially ordered cues – or questions. In turn, each cue has two branches according to how the question can be answered:

  1. If the answer to the question is yes, then the branch leads to the next question in the sequence.
  2. If the answer to the question is no, then the branch leads to an exit point in the sequence.

At the final cue in the sequence, both branches lead to an exit point to ensure that a decision is made either way.

Why is the fast-and-frugal tree useful in business?

Fast-and-frugal trees are particularly useful when decisions need to be made quickly. They are well suited to binary classification problems – or problems with elements occupying two possible outcomes.

FFTs have been trialed in emergency room scenarios to help physicians triage patients. During a peer-reviewed study, a classification tree of just three cues enabled doctors to diagnose and then direct patients to either a regular nursing bed or the coronary care unit. 

Cues were based on historical acute heart disease data, allowing high-risk patients to be identified quickly and accurately. In fact, the process was so accurate that it was a better predictor of heart disease than the clinical judgment of the physicians themselves.

Constructing fast-and-frugal trees

There are several ways to construct fast-and-frugal trees.

In the emergency room example, physicians had historical data on factors that lead to acute heart disease. Chest pain was one such predisposition, leading to the creation of a cue entitled “Chest pain chief symptom?” with a yes or no answer.

Although FFTs were designed to be simple, they have nonetheless been adapted by using more complex methods. Primarily, this is seen in FFTs that are constructed using a zig-zag algorithm.

Here, the tree is created using positive and negative cue validity. This validity is defined as the proportion of cases with a positive/negative outcome in all cases with a positive/negative cue value. Typically, the first – or “root” – cue of a zig-zag analysis tree is the cue with the greatest positive (or negative) validity. This ensures that the most significant positive and negative decisions are made first. 

Typically, cue validities are determined by using counts and ratios. In more advanced scenarios, they must be estimated using elements of probability theory such as conditional independence. Zig-zag decision trees enhance the already strong fundamentals of FFTs. Given that the tree can be completed with pen and paper, the accuracy of a zig-zag tree is as high as using a logistic regression model.

Fast-and-frugal tree applications

As noted, FFTs are useful in any situation requiring fast and accurate decisions or risk assessment. 

Beyond medical applications, these trees have been used in the military to identify enemy threats and also in courtrooms to decide whether to bail or jail a defendant.

In recent times, fast-and-frugal trees have also shone a light on how customer management decisions are made. Retail banking sales managers who embodied fast, frugal, and adaptive decision making were able to better anticipate client needs.

Key takeaways:

  • Fast-and-frugal trees are heuristic models that are useful for tasks where binary decisions or classifications need to be made.
  • Fast-and-frugal trees are made of sequentially ordered cues, otherwise known as questions. Each cue has a binary answer, with one answer leading to a subsequent question and the other leading to an exit point.
  • Fast-and-frugal trees are simple and effective decision-making tools. However, the decision-making process is enhanced by using historical data and aspects of probability theory.

Connected Thinking Frameworks

Convergent vs. Divergent Thinking

Convergent thinking occurs when the solution to a problem can be found by applying established rules and logical reasoning. Whereas divergent thinking is an unstructured problem-solving method where participants are encouraged to develop many innovative ideas or solutions to a given problem. Where convergent thinking might work for larger, mature organizations where divergent thinking is more suited for startups and innovative companies.

Critical Thinking

Critical thinking involves analyzing observations, facts, evidence, and arguments to form a judgment about what someone reads, hears, says, or writes.

Systems Thinking

Systems thinking is a holistic means of investigating the factors and interactions that could contribute to a potential outcome. It is about thinking non-linearly, and understanding the second-order consequences of actions and input into the system.

Vertical Thinking

Vertical thinking, on the other hand, is a problem-solving approach that favors a selective, analytical, structured, and sequential mindset. The focus of vertical thinking is to arrive at a reasoned, defined solution.

Maslow’s Hammer

Maslow’s Hammer, otherwise known as the law of the instrument or the Einstellung effect, is a cognitive bias causing an over-reliance on a familiar tool. This can be expressed as the tendency to overuse a known tool (perhaps a hammer) to solve issues that might require a different tool. This problem is persistent in the business world where perhaps known tools or frameworks might be used in the wrong context (like business plans used as planning tools instead of only investors’ pitches).

Peter Principle

The Peter Principle was first described by Canadian sociologist Lawrence J. Peter in his 1969 book The Peter Principle. The Peter Principle states that people are continually promoted within an organization until they reach their level of incompetence.

Straw Man Fallacy

The straw man fallacy describes an argument that misrepresents an opponent’s stance to make rebuttal more convenient. The straw man fallacy is a type of informal logical fallacy, defined as a flaw in the structure of an argument that renders it invalid.

Streisand Effect

The Streisand Effect is a paradoxical phenomenon where the act of suppressing information to reduce visibility causes it to become more visible. In 2003, Streisand attempted to suppress aerial photographs of her Californian home by suing photographer Kenneth Adelman for an invasion of privacy. Adelman, who Streisand assumed was paparazzi, was instead taking photographs to document and study coastal erosion. In her quest for more privacy, Streisand’s efforts had the opposite effect.


As highlighted by German psychologist Gerd Gigerenzer in the paper “Heuristic Decision Making,” the term heuristic is of Greek origin, meaning “serving to find out or discover.” More precisely, a heuristic is a fast and accurate way to make decisions in the real world, which is driven by uncertainty.

Recognition Heuristic

The recognition heuristic is a psychological model of judgment and decision making. It is part of a suite of simple and economical heuristics proposed by psychologists Daniel Goldstein and Gerd Gigerenzer. The recognition heuristic argues that inferences are made about an object based on whether it is recognized or not.

Representativeness Heuristic

The representativeness heuristic was first described by psychologists Daniel Kahneman and Amos Tversky. The representativeness heuristic judges the probability of an event according to the degree to which that event resembles a broader class. When queried, most will choose the first option because the description of John matches the stereotype we may hold for an archaeologist.

Take-The-Best Heuristic

The take-the-best heuristic is a decision-making shortcut that helps an individual choose between several alternatives. The take-the-best (TTB) heuristic decides between two or more alternatives based on a single good attribute, otherwise known as a cue. In the process, less desirable attributes are ignored.


The concept of cognitive biases was introduced and popularized by the work of Amos Tversky and Daniel Kahneman in 1972. Biases are seen as systematic errors and flaws that make humans deviate from the standards of rationality, thus making us inept at making good decisions under uncertainty.

Bundling Bias

The bundling bias is a cognitive bias in e-commerce where a consumer tends not to use all of the products bought as a group, or bundle. Bundling occurs when individual products or services are sold together as a bundle. Common examples are tickets and experiences. The bundling bias dictates that consumers are less likely to use each item in the bundle. This means that the value of the bundle and indeed the value of each item in the bundle is decreased.

Barnum Effect

The Barnum Effect is a cognitive bias where individuals believe that generic information – which applies to most people – is specifically tailored for themselves.

First-Principles Thinking

First-principles thinking – sometimes called reasoning from first principles – is used to reverse-engineer complex problems and encourage creativity. It involves breaking down problems into basic elements and reassembling them from the ground up. Elon Musk is among the strongest proponents of this way of thinking.

Ladder Of Inference

The ladder of inference is a conscious or subconscious thinking process where an individual moves from a fact to a decision or action. The ladder of inference was created by academic Chris Argyris to illustrate how people form and then use mental models to make decisions.

Six Thinking Hats Model

The Six Thinking Hats model was created by psychologist Edward de Bono in 1986, who noted that personality type was a key driver of how people approached problem-solving. For example, optimists view situations differently from pessimists. Analytical individuals may generate ideas that a more emotional person would not, and vice versa.

Second-Order Thinking

Second-order thinking is a means of assessing the implications of our decisions by considering future consequences. Second-order thinking is a mental model that considers all future possibilities. It encourages individuals to think outside of the box so that they can prepare for every and eventuality. It also discourages the tendency for individuals to default to the most obvious choice.

Lateral Thinking

Lateral thinking is a business strategy that involves approaching a problem from a different direction. The strategy attempts to remove traditionally formulaic and routine approaches to problem-solving by advocating creative thinking, therefore finding unconventional ways to solve a known problem. This sort of non-linear approach to problem-solving, can at times, create a big impact.

Bounded Rationality

Bounded rationality is a concept attributed to Herbert Simon, an economist and political scientist interested in decision-making and how we make decisions in the real world. In fact, he believed that rather than optimizing (which was the mainstream view in the past decades) humans follow what he called satisficing.

Dunning-Kruger Effect

The Dunning-Kruger effect describes a cognitive bias where people with low ability in a task overestimate their ability to perform that task well. Consumers or businesses that do not possess the requisite knowledge make bad decisions. What’s more, knowledge gaps prevent the person or business from seeing their mistakes.

Occam’s Razor

Occam’s Razor states that one should not increase (beyond reason) the number of entities required to explain anything. All things being equal, the simplest solution is often the best one. The principle is attributed to 14th-century English theologian William of Ockham.

Mandela Effect

The Mandela effect is a phenomenon where a large group of people remembers an event differently from how it occurred. The Mandela effect was first described in relation to Fiona Broome, who believed that former South African President Nelson Mandela died in prison during the 1980s. While Mandela was released from prison in 1990 and died 23 years later, Broome remembered news coverage of his death in prison and even a speech from his widow. Of course, neither event occurred in reality. But Broome was later to discover that she was not the only one with the same recollection of events.

Crowding-Out Effect

The crowding-out effect occurs when public sector spending reduces spending in the private sector.

Bandwagon Effect

The bandwagon effect tells us that the more a belief or idea has been adopted by more people within a group, the more the individual adoption of that idea might increase within the same group. This is the psychological effect that leads to herd mentality. What in marketing can be associated with social proof.

Read Next: Heuristics, Biases.

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