SAS® and software development best practice. Hints, tips, & experience of interest to a wide range of SAS practitioners. Published by Andrew Ratcliffe's RTSL.eu, guiding clients to knowledge since 1993
Tuesday, 21 January 2014
Estimation (Effort and Duration) #1/2
Beware. When we say we can't do estimates, it doesn't stop others doing the estimation on our behalf. The end result of somebody else estimating how long it'll take us to deliver a task is a mixture of inaccuracy and false expectations placed upon us. Our own estimates of our own tasks should be better than somebody else's estimate.
My personal belief is that anybody can (with a bit of practice and experience) make decent estimates, but only if they perceive that there is a value in doing so. In this article I'll address both: value, and how to estimate.
So, let's start by understanding the value to be gained from estimation. The purpose is not to beat up the estimator if the work stakes longer than estimated! All teams need to be able to plan - it allows them to balance their use of constrained resources, e.g. money and staff. No team has enough staff and money to do everything it wants at the same time. Having a plan, with estimated effort and duration for each activity, helps the team keep on top of what's happening now and what's happening next; it allows the team to start things in sufficient time to make sure they're finished by when they need to be; it allows teams to understand that they probably won't get a task done in time and hence the team needs to do something to bypass the issue.
Estimates form a key part of a plan. For me, the value of a plan comes from a) the thought processes used to create the plan, and b) the information gained from tracking actual activity against the planned activities and spotting the deviations. There's very little value, in my opinion, in simply having a plan; it's what you do with it that's important.
Estimates for effort or duration of individual tasks combine to form a plan - along with dependencies between tasks, etc.
Okay, so what's the magic set of steps to get an accurate, bullet-proof estimate?...
Well, before we get to the steps, let's be clear that an estimate is (by definition) not accurate nor bullet-proof. I remember the introduction of estimation in maths classes in my youth. Having been taught how to accurately answer mathematical questions, I recall that many of us struggled with the concept of estimation. In hindsight, I can see that estimating required a far higher level of skill than cranking out an accurate answer to a calculation. Instead of dealing with the numbers I was given, I had to make decisions about whether to round them up or round them down, and I had to choose whether to round to the nearest integer, ten or hundred before I performed the eventual calculation.
We use estimation every day. We tot-up an estimate of the bill in our heads as we walk around the supermarket putting things into our trolley (to make sure we don't go over budget). We estimate the distance and speed of approaching vehicles before overtaking the car in front of us. So, it's a skill that we all have and we all use regularly.
When I'm doing business analysis, I most frequently find that the person who is least able to provide detail on what they do is the person whose job is being studied. It's the business analyst's responsibility to help coax the information out of them. It's a skill that the business analyst needs to possess or learn.
So, it shouldn't surprise us to find that we use estimation every day of our life yet we feel challenged to know what to do when we need to use the same skills in a different context, i.e. we do it without thinking in the supermarket and in the car, yet we struggle when asked to consciously use the same techniques in the office. And, let's face it, the result of an inaccurate estimate in the office is unlikely to be as damaging as an inaccurate estimate whilst driving, so we should have confidence in our office-based estimations - if only we could figure out how to do it!
We should have confidence in our ability to estimate, and we should recognise that the objective is to get a value (or set of values) that are close enough; we're not trying to get the exact answer; we're trying to get something that is good enough for our purposes.
Don't just tell your project manager the value that you think they want to hear. That doesn't help you, and it doesn't help the project manager either.
Don't be afraid to be pessimistic and add a fudge factor or contingency factor. If you think it'll take you a day then it'll probably take you a day and a half! I used to work with somebody who was an eternal optimist with his estimations. He wasn't trying to pull the wool over anybody's eyes, he honestly believed his estimations (JH, you know I'm talking you!). Yet everybody in the office knew that his estimations were completely unreliable. Typically, his current piece of work would be "done by lunchtime" or "done by the end of today". We need to be realistic with our estimations, and we need to look back and compare how long the task took compared with our estimation. If you estimated one day and it took two, make sure you double your next estimation. If somebody questions why you think it'll "take you so long", point them to your last similar piece of work and tell them how long it took you.
When creating and supplying an estimate it's worth thinking about three values: the most likely estimate, the smallest estimate, and the biggest estimate. For example, if I want to estimate the time it might take to develop a single DI Studio job that requires a significant degree of complexity, perhaps I can be sure it'll take at least a couple of days to develop the job, certainly no more than two weeks. Armed with those boundaries, I can more confidently estimate that it'll take one week.
If you're not confident with your estimates, try supplying upper and lower bounds alongside them, so that the recipient of your estimates can better understand your degree of confidence.
Tomorrow I'll get into the meat of things and offer my recipe for estimation success.