3 Common mistakes when making estimations
Currently I am creating an Excel sheet that I am using to monitor the progress of the project I am currently working. Working on this Excel sheet made me aware of some common mistakes people often make while making estimations. Here are 3 of the most common mistakes:
1. Forgetting that you will probably NOT be working full time on your project.
When you work 8 hours a day, it is often the case that you won’t be working 8 hours full time on your project. People disturb you, you have some meetings you need to attend, you spend some time answering email, you’ve got a brainstorm session, you need to go out to meet the customer, etc. Not working full time on your project means that your focus factor is not 100%. If you call everything else a ‘disturbance’ of effective work time, it might be interesting to figure out how much of your time is spent on disturbances and how much of your time is effectively spent on your project. The project I am currently working on will eventually turn out to have a focus factor of around 80%, which means that 20% of my time at work is spent at meetings, etc.
2. Forgetting the number of hours you have available
If you’re working in a team where some of your team members are part time employees, you will have less available hours to get the work done than a team consisting only of full time employees. Although this sounds logical, available hours is something that is quite often not taken into account.
3. Forgetting that productivity / speed will change over time and can be hard to estimate in advance.
If you’re starting a project with a new team, it will be difficult to estimate how fast your team will work. Once you have worked together for some time, you will (if you measure it) gain some knowledge of how much work your team can complete in a certain period of time. Without this experience as a team, you have to base your estimation on wild guesses and experience with other teams that may be different than this one. It is also very hard to estimate how long something will take when you’re going to do something that is entirely new for you: will it be easy? Will it take lots of study time to master it? Also, you will probably get better at the tasks you’re about to be doing. This means that an estimation of 4 days in the beginning of a project could be only 3 days once you’re familiar with the tasks at hand. Making relative estimations can be a solution to decouple time from size. If you estimate in absolute or fixed days, you are actually ignoring the fact that you’re team will get better and faster along the way.
Example:
Say, you estimate that some task takes 4 days. Now, if you have a focus factor of 80%, this means that the work will take 5 days to complete. Now, if this person only works 4 hours a week, this will mean that if he starts on Monday, has a focus factor of 80% and 1 part time day off, then the task won’t be finished until Monday next week in the end of the day.
So remember that you always take into account that you won’t be working full time on a project, and that you have a (limited) number of hours available for your project. Also take into account that estimations at the beginning of a project may be unrealistic further in time. Remember this when determining a deadline, or deciding which parts of the project will be skipped in order to make it to the deadline.
