Planning fallacy

The planning fallacy (English planning fallacy ) is the tendency of people and organizations to underestimate how much time they need to complete a task. The English term was first proposed by Daniel Kahneman and Amos Tversky in a publication of 1979. The effect allows predictions for a wide range of tasks, including filling out tax documents, homework, the construction of furniture, programming and origami. The fallacy only affects predictions about their own tasks; when outside observers predict the completion time of a task, they show a pessimistic tendency and overestimate the time required. Lovallo and Kahneman proposed in 2003 an expanded definition of the planning fallacy before: as the tendency of the time, costs and / or risks of future actions to be underestimated, while overestimating the benefits of these actions. By this definition, the planning fallacy not only leads to exceeding the planned timeframe, but also to exploding costs and fewer benefits than planned.

Studies and examples

In a 1994 study, 37 psychology students were asked to estimate how long it would take for the completion of their theses. The average estimate was 33.9 days. They also estimated how long it would take " if everything would run as good as possible " ( with an average of 27.4 days ) and " when everything was going so badly as possible " ( with an average of 48.6 days ). The actual average time for completion was 55.5 days, with only 30 % of the students presented their work done in the predicted time.

Another study commissioned students to guess when they would complete a study-related project. The researchers asked about the estimated times at which the students expected with 50 %, 75%, and 99 % probability, to cope with their projects.

A survey of Canadian taxpayers, which was published in 1997, reported that respondents einschickten their tax documents about a week later than predicted. They were aware of their past difficulties, send the documents in time, aware, but expected the next time to come faster. This illustrates an important feature of the planning fallacy; that people recognize their past forecasts as excessively optimistic, and at the same time insist that their current forecasts are realistic.

Explanations

Kahneman and Tversky original statement was that people focused on when planning the most optimistic scenario for the task, instead of using their full experience, how long does similar tasks. One explanation that has been offered by Roger Buehler and colleagues, is wishful thinking: people think that tasks are completed quickly and easily, because they want that this is the case. In another publication Buehler and colleagues suggest an explanation based on the self-esteem- relevant distortion of past performance. By tasks that went out well, taking credit, but blame for delays outside influences can get people past experiences with poor scheduling aside to. An experiment showed that the optimistic bias is absent when people made ​​their predictions anonymous. This suggests that people give optimistic estimates to make a positive impression on others.

It tries to explain the planning fallacy in the context of impression management theory was.

Planners tend to focus their attention on the project, and the time for illness, vacation, meetings and other additional expenses to be underestimated. They also tend not to plan projects to such a level of detail that would allow the prediction of individual tasks, such as placing a brick in a wall. This promotes unrealistic optimism (English optimism bias) and prevents the time required can be predicted by measurements, such as the timing for placement of a tile and then multiplying with the number of bricks. In addition, fall complex projects that have no fixed targets, often a creeping expansion of the project objectives (English mission creep ) for sacrifices. As Fred Brooks reported in The Mythical Man -Month, adding additional staff due to an already late project in a number of risks and additional costs which further delayed the project may even. This is known as the " Brooksche law."

Another possible explanation is the need to obtain the approval for the project (English imperative authorization ): A large part of the project planning takes place in a context in which the approval of funds is required to proceed with the project. Since the end of the plan is often keen to get the project approved, these dynamics can lead to the end of the plan cost and effort deliberately underestimated. It is easier to get in arrears forgiveness of financial or contracting for overdrafts, but to get at the beginning of a permit for the project with a realistic cost estimate.

Methods to avoid the planning fallacy

Daniel Kahneman, Amos Tversky and Bent Flyvbjerg developed the so-called reference class forecasting to eliminate the effects of the planning fallacy in making decisions or reduce. The prediction based on the results of similar situations in the past is created.