How do you estimate how long a trip to the supermarket is?

Most often, people simply rely on their intuition for the answer. When they think of this question, an answer comes to mind immediately – say, 20 minutes. This answer is error prone, especially if you are shopping at a new supermarket.

The second alternative is to break the shopping trip into chunks and estimate each chunk separately.

- Travel to and fro: 14 min
- Shopping for 20 items: 10 min
- Checkout and payment: 5 min
- Total: 29 min

This estimate is more accurate than blind intuition. However, it still needs some buffer. Just in case you lined up behind the gentleman who rummages through two purses for the ’17 cents’ portion of his bill.

The third alternative is statistical – to gather data from several shopping trips, calculate the mean and the standard deviation. This estimate is the hardest to calculate, but is the most robust.

Each estimation method I have listed out here is harder more reliable than the previous one. We often default to the easiest option, with little regard for how error-prone it can be.

Not all estimations are as trivial as a trip to the supermarket. Several deadlines we set have repercussions on our colleagues, clients and their families. In those cases, we are better off is slowing down and taking more time to provide an estimate rather than burning at both ends to meet an impossible deadline.

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