I work for QSM, a leading software project estimation and demand management company. We focus on top-down estimation, meaning we figure out the total project duration and effort before any detailed planning occurs. We use SLIM-Estimate also known as the Putnam Model. Larry Putnam Sr. introduced SLIM in 1978. It is one of the leading software estimation tools in the world, validated with over 35 years of industry leading research and updated regularly with the latest technologies. 

Many people call us for help with team size software project estimation, they want to see how many people it’s going to take to deliver a specified amount of functionality within a certain duration and budget. At the time they call us they are often using task level planning tools to try to figure this out. 

The problem is that it’s tough to allocate people and the number of hours they will work when they haven’t figured out the specific requirements of each task and when they haven’t estimated the total duration and effort for the overall system. A manager could spend days creating a task level plan that doesn’t add up to the overall project duration and budget that is needed to deliver the functional requirements. When it doesn’t add up then re-planning has to take place costing more time and money. This is why QSM recommends estimating the big picture first, the scope level. 

At QSM, we have one of the largest industry databases in the world of completed software projects. The data comes from our clients with their permission and this data has been the backbone of our software estimation business for over 35 years. We can see what is reasonable on software development projects as it relates to cost, team size, effort, duration, size, and reliability. Because of our experience we are often asked about risk factors and estimation accuracy early in the project lifecycle. We explain that increased accuracy comes with having historical data and good sizing information.

But what happens on the early estimates when clients don’t have history and detailed sizing information? Can they still generate scope level estimates so they can make good business decisions? The answer is yes. Risk management techniques can be applied and project uncertainty can be calculated so organizations can plan effectively. This is very important because big business decisions are often made early. Decision-makers need to know if they should move forward with a project and they need to know how much time and effort to allocate.

We use SLIM-Estimate, which is a leading estimation tool that leverages the Putnam Model. It generates reliable estimates based on QSM’s time-tested forecasting models and historical data and it also provides scope level estimates when project information is hard to find. It will allow you to see the chance you have of hitting your project goals and it will allow you to factor in your uncertainty.

Since I work for a software metrics and estimation company, many people ask me questions regarding capacity planning and demand management. Most of the project managers that I speak with are using project portfolio management tools for very detailed, task-level resource capacity planning. They spend a lot of time planning the person hours for each task and then these task-level plans are prioritized and viewed across the organization. These are useful tools and methods and they usually require a sizable investment.

The problem is that many of these project managers don’t have a good way to support demand management. That is to say that they aren’t able to accurately estimate the key drivers that go into their PPM tools.  They need to be able to answer key questions like: Should we commit to 6 months or 9 for the project duration? Do we need 10 software developers or 20 to finish in 9 months? How much is the overall project going to cost? What alternatives do we have? Has anyone ever achieved that duration in the past? Should we even go forward with this project; what is the risk?

Oftentimes the project manager comes up with this information informally based on experience. Unfortunately, when they don’t use a scientific approach to estimating, they leave out key factors that affect the estimate and project success, like project complexity, team efficiency, and overall project uncertainty.

One of the most common objections we hear from companies with regard to getting started with top-down estimation is that it’s not needed, because they already have a detailed planning spreadsheet in place. Customers will concede that their estimation practices are not perfect, but that they are working “OK.” But, when it comes to spending your company’s money on software projects is “OK” enough?