Improving estimate accuracy

targetDon’t we just get frustrated when our estimates or guesstimates on timescales or costs turn out to be different from what actually happens? So how do we improve the accuracy of our estimates?

What do we need estimates for?

This is a golden question – ask yourself this whenever you do an estimate. It’s a lean principle to remove waste (i.e. non-value adding activity). If the estimate information you are producing isn’t vital for making a decision, then take a good hard look as to whether you need it. Some of the teams I have worked with have stopped some kinds of estimates as these estimates were not changing the decision.

Why are estimates uncertain?

Estimates are uncertain because we lack information. We’ve never built this particular feature before. We don’t exactly know what we need to do. As we work further with the feature, we gain more information and our uncertainty about how much work is required reduces. This leads to the idea of the cone of uncertainty shown below which suggests that uncertainty decreases (and hence accuracy of estimate increases) throughout the life of a feature.

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What helps improve estimating accuracy?

1. Break work down

If you only do one thing, break the work down into smaller pieces (this is a core lean principle!) It’s much easier to estimate smaller activities than larger ones. By simply breaking down large work items into smaller pieces, your estimating accuracy will improve.

2. Increase the rate at which the estimator gains experience

Ability to estimate comes from learning from past experience of estimating. So get more experience! The way you increase your learning rate is to shorten the cycle time i.e. the time it takes to produce something. Doubling the cycle time doubles the rate of learning! Of course, the experience gained needs to be effectively captured (retrospectives, low staff turnover, etc.).

3. Ensure estimators are the people who are doing the work

Seems simple but in a lot of cases, the people doing the estimating are far from the actual work (or, sometimes, estimates are adjusted by people far from the work!)

4. Reduce dependencies

Typically if a task requires 90% of one person and 10% of another, the 10% person will be the bottleneck because his focus is not on the task. This means that it’s difficult for him/her to be available precisely when needed. Eliminating this dependency will reduce variation in timelines. Feature teams help with this.

5. Get multiple inputs

Agile teams often use planning poker to harness the brainpower of the entire team to improve the estimate – it’s unlikely that one person has all the best information. This is a fun and easy thing to try.

6. Agree on which estimate we want

Many timeline estimates are simply the earliest possible time for which the probability of delivery is not zero. Did you want the most likely date (50% chance of being early, 50% chance of being late) or the date for which it is almost certain delivery will have happened by? Make sure everybody agrees which estimate we are talking about.

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7. Understand the politics

There are also all sorts of human dynamics that can skew your estimate. For example:

  • If there are “punishments” for getting it wrong, folk tend to add buffers to their estimates.
  • If folk believe that the uncertainty associated with the estimate will not be communicated clearly (for example to senior management) then they tend to add buffers. A solution to this that a lot of agile teams use when they are doing an early guesstimate is to use “T-shirt” sizing whereby the estimate is classified as Small, Medium, Large or Extra Large. Communicating guesstimates like this makes it clear that they are not very accurate.
  • If there is already a target declared (“we want this to be under $100k” or, “we want to complete this by June”) then folk tend to be anchored by that and don’t like to say it’s not possible. We all like to please our stakeholders.
  • Many fascinating studies show that people have a natural subconscious tendency to be overconfident in their estimating skills. If the estimator(s) have little data on past performance to help correct this, then its likely they will underestimate tasks.

 

Setting expectations on estimate accuracy

It’s tempting to set a team a goal to improve estimate accuracy. The risk with this (which I have seen in some teams) is that the quickest and simplest way of improving estimating accuracy is either to add undeclared buffers or to invest more time and resource before making the estimate. The latter effectively moves estimate creation to later in the lifecycle which destroys the purpose of the estimate (which is to make decisions early on in the lifecycle).

A better way of improving estimating accuracy is to set the team goals on reducing cycle time and reducing the size of items flowing thro’ the pipeline (as per the first two points above). By focusing on these general lean-agile practices, we also get an improvement in estimating accuracy!

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