Planning Fallacy..
In a 1994 study, 37 psychology students were asked to estimate how long it would take to finish their senior theses. The average estimate was 33.9 days. They also estimated how long it would take "if everything went as well as it possibly could" (averaging 27.4 days) and "if everything went as poorly as it possibly could" (averaging 48.6 days). The average actual completion time was 55.5 days, with only about 30% of the students completing their thesis in the amount of time they predicted.
The researchers asked their students for estimates of when they (the students) thought they would complete their personal academic projects, with 50%, 75%, and 99% confidence.
• 13% of subjects finished their project by the time they had assigned a 50% probability level;
• 19% finished by the time assigned a 75% probability level;
• 45% (less than half) finished by the time of their 99% probability level.
In project management, this is sometimes referred to as Hofstadter’s Law: It always takes longer than you expect, even when you take into account Hofstadter’s Law. (Douglas Hofstadter was the author of the 1979 work Gödel, Escher, Bach.) There are a number of theories as to why this is so often true. To my mind, the best explanation comes from Elihu Goldratt in his 1997 Critical Chain, which analyzed project management issues from a different perspective.
Goldratt argued that when asked to estimate task duration, people tended to give a safe estimate whenever possible. Knowing the estimate had safety built in, people then tended to procrastinate or attack other problems until the actual time available was insufficient to get the job done. This is also known as Parkinson’s Law, the tendency of work to expand to fill the time available for its completion.
Numerous books try to point out solutions, but the problem persists.
The researchers asked their students for estimates of when they (the students) thought they would complete their personal academic projects, with 50%, 75%, and 99% confidence.
• 13% of subjects finished their project by the time they had assigned a 50% probability level;
• 19% finished by the time assigned a 75% probability level;
• 45% (less than half) finished by the time of their 99% probability level.
In project management, this is sometimes referred to as Hofstadter’s Law: It always takes longer than you expect, even when you take into account Hofstadter’s Law. (Douglas Hofstadter was the author of the 1979 work Gödel, Escher, Bach.) There are a number of theories as to why this is so often true. To my mind, the best explanation comes from Elihu Goldratt in his 1997 Critical Chain, which analyzed project management issues from a different perspective.
Goldratt argued that when asked to estimate task duration, people tended to give a safe estimate whenever possible. Knowing the estimate had safety built in, people then tended to procrastinate or attack other problems until the actual time available was insufficient to get the job done. This is also known as Parkinson’s Law, the tendency of work to expand to fill the time available for its completion.
Numerous books try to point out solutions, but the problem persists.
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