There is a suggestion that only the final target of a project's performance is needed to steer toward success. This target can be budget, a finish date, the number of stories or story points in an agile software project. With the target and the measure of performance to date, collected from the measures at each sample point, there is still a missing piece needed to guide the project.
With the target and the samples, no error signal is available to make intermediate corrections to arrive on target. With the target alone, any variances in cost, schedule, or techncial performance can only be discovered when the project arrives at the end. With the target alone, this is an Open Loop control system.
- Is a non-feedback system, where the output – the desired state – has no influence or effect on the control action of the input signal — the measures of performance are just measures. They are not compared to what the performance should be at that point in time.
- The output – the desired state– is neither measured nor “fed back” for comparison with the input — there is not an intermediate target goal to measure the actual performance against. Over budget, late, missing capabilities are only discovered at the end.
- Is expected to faithfully follow its input command or set point regardless of the final result — the planned work can be sliced into small chunks of equal size - this is a huge assumptions by the way - but the execution of this work must also faithfully follow the planned productivity. (See assumptions below).
- Has no knowledge of the output condition – the difference between desired state and actual state – so cannot self-correct any errors it could make when the preset value drifts, even if this results in large deviations from the preset value — the final target is present but the compliance with that target along the way is missing, since there is no intermediate target to steer toward for each period of assessment - only the final.
- The needed performance in terms of stories or any other measure of performance are linear and of the same size - this requires decompsong the planned work for each period to nearly identical sizes, work efforts, and outcomes.
- The productivity of the work performed is also linear and unvarying - this require zero defects, zero variance in the work effort, and sustained productivity at the desired performance level.
- Irreducible Uncertainty - this is the noise of the project. Random fluctuations on productivity, technical performance, efficiency, effectiveness, risk. These cannot be reduced. They are Aleatory Uncertainties.
- Reducible Uncertainty - these are event based uncertainties that have a probability of occurring, have a probability of the consequences, and have a residual probability that when fixed will come back back again.
Irreducible Uncertainty can only be handled with Margin. Cost margin, schedule margin, technical margin. This is the type of margin you use when you drive to work. The GPS Navigation system says it 23 ninutes to the office. It's NEVER 23 minutes to the office. Something always interferes with our progress.
Reducible Uncertainty is handled in two way. Spending money to buydown the risk that results from this uncertainty. Management Reserve (budget reserve and schedule contingency) to be used whenm soemthnig goes wrong to pay for the fix when the uncertainty turns into reality.
The next figure (page 28) shows how to manage in the presence of these uncertainties, by measuring actual performance against the desired performance at each step along the way.
In this figure, we measure at each assessment point the progress of the project against the desired progress - the planned progress, the needed progress. This planned, desired, or needed progress is developed by looking at the future effort, duration, risk, uncertainty - the stochastic processes that drive the project - and determining what should be the progress at this point in time to reach our target on or before the need date, at or below the needed cost, and with the needed confidence that the technical capabilities can be delivered along the way? This is closed loop control.
The planned performance, the needed performance, the desired performance is developed early in the project. Maybe on day one, more likely after actual performance has been assessed to calibrate future performance. This is called Reference Class Forecasting. With this information estimates of the needed performance can then be used to establish steering targets along the way to completing the project. These intermediate references - or steering - points provide feedback along the way toward the goal. They provide the error signal needed to keep the project on track. They are the basis of Closed Loop control.
In the US, many highways have rumble strips cut into the asphalt to signal that you are nearing the edge of the road on the right. They make a loud noise that tells you - hey get back in the lane, otherwise you're going to end up in the ditch.
This is the purpose of the intermediate steering targets for the project. When the variance between planned and actual exceeds a defined threshold, this says hey, you're not going to make it to the end on time, on budget, or with your needed capabilities if you keep going like this.
Kent Beck's quote is...
Optimism is the disease of software development. Feedback is the cure.
This feedback must have a reference to compare against if it is to be of any value in steering the project to a successful completion. Knowing it's going to be late, over budget, and doesn't work when we arrive at late, over budget, and not working is of little help to the passengers of the project.