Academic journal article Memory & Cognition

Bias in Memory Predicts Bias in Estimation of Future Task Duration

Academic journal article Memory & Cognition

Bias in Memory Predicts Bias in Estimation of Future Task Duration

Article excerpt

Both anecdotal accounts and experimental evidence suggest that people underestimate how long it will take them to complete future tasks. A possible reason for this tendency is that people remember tasks as taking less time than they actually did, with these biased memories causing a corresponding bias in prediction. Two experiments were performed to determine whether or not a systematic bias in memory could explain a similar systematic bias in prediction. In support, it was found that (1) the tendency to underestimate future duration disappears when the task is novel, (2) there is similar bias in estimation of both past and future durations, and (3) variables that affect memory of duration, such as level of experience with the task and duration of delay before estimation, affect prediction of duration in the same way. It appears that, at least in part, people underestimate future event duration because they underestimate past event duration.

It often takes people longer than planned to finish tasks. Even though people are aware that their estimates have come up short in the past, they continue to underestimate the duration of future projects. Studies have shown underestimation for such tasks as writing papers, performing everyday and school tasks, completing a computer assignment (Buehler, Griffin, & Ross, 1994; Connolly & Dean, 1997; Griffin & Buehler, 1999; Koole & Spijker, 2000; Newby-Clark, Ross, Buehler, Koehler, & Griffin, 2000; Taylor, Pham, Rivkin, & Armor, 1998), building a computer stand (Byram, 1997), doing a spell check task (Francis-Smythe & Robertson, 1999), completing tax forms (Buehler, Griffin, & MacDonald, 1997), finishing Christmas shopping (Buehler & Griffin, 2003), completing Web development projects (Mol0kken & J0rgensen, 2005), programming software (J0rgensen & Sjeberg, 2001 ), reading a manuscript (Josephs & Hahn, 1995), and waiting in line for gas (Konecni & Ebbesen, 1976).

In the business world, underestimation of task duration has numerous negative consequences: missed deadlines, budget overruns, terminated contracts, and loss of business. These negative effects of task underestimation may be quite large in the multimillion dollar software design business (Connolly & Dean, 1997).

The memory bias account (Roy, Christenfeld, & McKenzie, 2005) supplies a possible explanation for this tendency to underestimate future duration: Our memories for past durations are incorrect, causing corresponding errors in prediction. People remember past task durations as being shorter than they actually were, and therefore, when they consult them to predict the next task, they underestimate how long that task will take.

Memories of past task durations will generally be based on estimates, rather than on actual measured durations, since it is rare that people know the exact beginning and ending times of tasks, especially when the task is completed over a number of different sessions. Studies of software development companies have shown that the people in charge of predicting how long projects will take rarely know the actual duration for previous, similar projects (Jørgensen & Sjaberg, 2001; Moløkken & Jørgensen, 2005). Furthermore, research has indicated that there is a tendency to underestimate task duration retrospectively (for reviews, see Block & Zakay, 1997; Fraisse, 1963; Poynter, 1989; Wallace & Rabin, 1960). If people rely on estimations and estimations tend to be short, predictions are likely to underestimate actual durations.

It is unlikely that when people predict future duration, they recall every past instance of similar tasks and estimate the duration for each. At times, people may recall the duration of a specific instance, but they may also call upon a more general representation that they have for that task that is based on past experience. This past experience could be one of performing the task directly or observing others. …

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