To Plan or Not to Plan? A Mixed-Methods Diary Study Examining When, How and Why Knowledge Work Planning is Inaccurate

Reliable and accurate planning is essential for modern knowledge workers. However, there is limited insight about when, how and why planning is inaccurate, and the circumstances in which those inaccuracies are troublesome. To investigate this, we asked 20 academics to keep a diary for a single work day. They estimated the duration of the tasks they wanted to achieve at the start of the day and noted down in detail the tasks they actually achieved during the day. Semi-structured interviews were conducted to complement this diary data. The diaries showed that some tasks, such as email and coding, were more susceptible to time underestimation bias while other tasks, such as writing and planning, were more susceptible to time overestimation bias in planning. Based on interviews, a typology of common reasons for delays in planned daily work is presented. It suggests that vague and optimistic planning leads to the observed discrepancy between planned and actual work. Finally, interviews suggested that participants adopted four planning strategies that vary in the frequency of planning, from minimal planning to daily, weekly and multi-level planning. We close by discussing ways support systems for accurate planning can be better designed for different use cases. © 2021 ACM.