Successful Project Managers Road Map by Mostafa Alshimi - HTML preview

3- How to estimate more  accurately

Estimating activity duration accurately is important to the success of any  project. You and your team estimate the various requirements of cost,  time, and resources throughout your project. Although activity duration  estimation looks at the time it takes to complete the entire project,  activity duration estimation is dependent on other time and resource  estimates.

You might start on these estimates at the inception of the project, but you  make the most of the estimates during the planning phase. It's a good  idea that all the people who implement the plan participate in preparing  It.   Estimates are never exact. That's their nature — they are best guesses.  But you can improve your accuracy by dividing the estimation task into  three distinct steps: determining a Work Breakdown Structure (WBS),  estimating the amount of work and duration of work packages, and  calculating the project schedule.

1- Determine the Work Breakdown Structure (WBS): The Work  Breakdown Structure (WBS) is an estimating tool that defines a  project in terms of its deliverables. The WBS also provides a  method for breaking down deliverables into meaningful units of  work. With this breakdown, you establish the work hierarchy and  create a foundation for the other elements of the estimating  Process.

A WBS is divided into work levels. Work packages are at the  lowest levels (or "end nodes") of each branch of your WBS. A work  package usually refers to a unit of work to be performed within  your organization.

Get your stakeholders involved when you start on your WBS. They  can provide information on tasks and resources that might  otherwise be overlooked. Generally, the more complete your  WBS, the more accurate your duration estimate.

When creating your WBS:

a. Develop your WBS before scheduling or allocating resources.

b. Do not use your WBS to show the work sequence.

c. Involve knowledgeable individuals in your WBS development.

d. Break down your project only as far as you must for accurate estimation.

e. Do not force all paths on your WBS down to the same level.

f. Use no more than 20 levels.

2- Estimate the duration of work packages: The duration of a work  package is equal to the amount of time required to do the work,  divided by the number of people working (duration=work/number  of people). 

After you have the raw estimate for a work package, you need to  add some padding to get a realistic number. The padding accounts  for real-life factors such as:

• Lost time Team members and workers are not available  five days per week, 52 weeks per year. Personal or public  holidays, sickness, training, group meetings, family  emergencies, and other events affect the time that  workers can spend on the job. Keep these factors in mind  when you calculate the duration of work packages. You  can use enterprise calendars in project-tracking systems,  such as Microsoft Office Project Professional 2003, to help  you make accurate estimates that allow for these time  Losses.

• Part–time work Assigning part–time work on a given  work package lengthens its duration. Half–time work  doubles the duration, three–quarter work adds 50% to  the duration, and so on. Consult personal schedules and  work hours when calculating the effect of part–time work  on your estimate.

• Interference Physical constraints or features of the work  location can have a negative impact on effectiveness and  increase work package duration. Areas with limited access  or workspace might cause workers to get in each other's  way or limit their use of facilities. For instance, in a room  that accommodates only one worker at a time, adding  another worker does not decrease duration, but might  add to it instead. Fax machines, phones, noise, proximity  of machinery, placement of equipment, and even traffic  flow might cause interference. As interference rises,  productivity falls and work duration rises. Take into  account the possible interference factor when you make  your duration estimate.

• Communication Communication takes time. While  communication is good, trying to communicate too much  between too many team members can increase work  duration. The number of communication channels grows  exponentially as the number of team members increases.  Messages can also lag when distance and time–zone  differences are involved. Include the communication  factor in your estimate.

Experience and the use of historical data also improves  your estimates. If you've done a task frequently — or have  a lot of documentation for similar tasks — you'll know the  task's average duration. After you know the level of  human resources available to do the work, you can use  this average in calculating your estimate. But because  estimates are not exact, an average duration is only that  — an average. In practice, the duration has a 50% chance  of being higher or lower than the average.

With this in mind, it's tempting to pad your estimate a lot  and increase the probability that the work is completed  on time or ahead of time. But beware: Pad with care. Over  padding increases budget costs. If your budget is too fat,  your project might not get funded.

Some projects don't lend themselves well to standard  estimating techniques. Historical data becomes  particularly useful in these cases. For instance, most  software projects are not mechanistic and activities can  be indeterminate, so estimating project duration for  software development has always been difficult. But by  tailoring their model to their needs and using historical  data about similar projects, many software companies  produce better estimates than ever before. Using  historical data provides a key to better estimation.

3- Calculate the project schedule: When your WBS is complete and  you have duration estimates for all the work packages, you and  your project team can determine the overall project duration. The  two most common estimating methods for this are the Critical  Path Method (CPM) and the Performance Evaluation Review  Technique (PERT).

The differences between CPM and PERT are:

• CPM calculates the total project duration based on individual task  durations and their interdependencies. The sequence of tasks  determining the minimum time needed for the project is the  critical path.

• PERT is a pictorial description of project tasks as a network of  dependencies. Although it is also concerned with critical paths,  PERT looks at the most likely time estimates for tasks and  boundary times (time windows) for tasks.

Next, you need to know the early start and finish dates, the late start and  finish dates, and the float. Calculate the early start and finish dates by  using software which is very commonly used nowadays.

When you've identified the early start and finish dates, the late start and  finish dates, and the float, you and your project team can identify the  critical path. The critical path is the shortest path on the project. If a task  on the critical path is delayed, the entire project is delayed.

With all this information assembled, you can calculate your schedule and  complete your estimate of project duration.

Final estimate: A structured and disciplined approach to estimating  project duration helps you create a comprehensive estimate that reflects  real tasks and real-world scheduling. This approach removes uncertainty  and creates a project plan that helps you know your options and adapt to  path changes. Sound duration estimation also supports realistic budget  estimates that increase your project's chance of success. Even though  estimates are never exact, solid data and good estimating practices make  your "best guesses" better.

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