Planning in Scrum: planning and variance (1/2)

This article is one of two about Planning in Scrum

We humans really suck at planning. We can plan simple things pretty accurate: cleaning the house, food preparation, repetitive labor. Planning improves if we do the same or similar tasks often. We learn it by doing. But for the rest? Planning of anything that isn't simple is hard.

One of the things that surprises me is that we don't get taught planning in school. In high school teachers assume the students can plan, but it has never been taught in primary school. And it doesn't improve after high school either. There is a general assumption that everybody can plan, although we all know we can't.

Planning

Planning is about three things, the first one is time, the second one is breakdown and the third one is order. When we talk about time we want to know how much time we need to complete the work. We can guestimate that vacuuming the living room will take approximately half an hour. But we also know that there can be a slight variance in time. Which means that all time estimations should carry a variance with them. We should say: "vacuuming the living room will take me half an hour plus or minus five minutes or between 25 and 35 minutes". 

For bigger tasks we need to break them down in smaller task we can comprehend and plan. So if there is the task of vacuuming the entire house, we should break it up in vacuuming per room. Smaller tasks are easier to understand and guestimate. 

Last but not least we need to take into account that there is an order in doing things. Vacuuming the attic, then the basement and then the living room doesn't sounds like a practical order. We must reorder to optimize our work plan. All in all planning is more then just a time estimate and even that is worthless without knowing the variance.

Variance

Variance is the deviation from the norm. So if we plan an hour and it can be either five minutes shorter or longer, the variance is five minutes. All estimation should have a variance to predict minimum and maximum time needed. The time we need is only known in hindsight, but should be somewhere between min and max. The larger the estimation, the larger the variance. The ratio between estimation and variance is not linear. It is more exponential. This means that the bigger the job, the bigger the variance can be. And the variance will grow more compared to the increase in time. Which enforces the need to breakdown work.

Conclusion

Planning is hard to master, it takes three ingredients: time, breakdown and order. And when talking about time, always mention the variance.

Next week we talk about story points and planning poker