436. ITTO
Process group process ITTO Value
Planning
Outputs Schedule Management Plan
Define Activities
Sequence Activities
Precedence Diagramming Method (PDM) Dependency Determination
Leads and Lags
Outputs Project Schedule Network Diagrams Project Document Updates
Outputs Activity Duration Estimates Project Document Updates
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Proj Schedule Network Diagrams Activity Resource Requirements
Proj. Mgmt Plan Updates Proj. Doc Updates
Organizational Process Assets Updates
437. We also saw the term decomposition used in the Scope Management chapter, in the Create WBS process.
Carefully read exam questions using the term. If the team is decomposing work into work packages (deliverables), they are creating a WBS (part of scope management).
If they are decomposing work packages into the activities required to produce them, they are in the Define Activities process.
So what do you need in order to define activities? That question is all there really is to the concept of inputs.) You need your schedule management plan, created in the previous process, and the scope baseline (scope statement, WBS, and WBS dictionary) from scope management.
You may also refer to organizational process assets including existing templates, historical information such as activity lists from other similar project, and any standards, such as a prescribed scheduling methodology.
Involving the team in the Define Activities process helps define the activities completely and accurately and therefore makes the estimates, created later in the planning process, more accurate.
438. Things to know about estimating for the exam
The next two time management processes-Estimate Activity Resources and Estimate Activity Durations-and the Estimate Costs process (see the Cost Management chapter) all involve estimating.
The following are important points to understand about time and cost estimating for the exam.
Management plans provide the basis for estimating.
Estimating should be based on a WBS to improve accuracy.
Time and cost estimates are interrelated, as time estimates may impact cost, and vice versa.
Identified risks must be considered when estimating time and cost of project work.
Estimating should be done by the person doing the work whenever possible to improve accuracy.
Historical information from past projects (part of organizational process assets) is key to improving estimates.
Schedule, cost, and scope baselines should be kept and not changed except for approved project changes.
The project schedule activities should be managed to the schedule baseline for the project.
The project costs should be managed to the cost baseline for the project.
Changes are approved in integrated change control.
Estimates are more accurate if smaller-size work components are estimated.
Changes should be requested when problems with schedule, cost, scope, quality, or resources occur and cannot be solved by using time and cost reserves.
A project manager should never just accept constraints from management, but should instead the needs of the project, come up with his or her own estimates (based on input from the team members doing the work when possible), and reconcile any differences to produce realistic objectives
The project manager may periodically the estimate to complete (ETC) for the project. in order to make sure adequate time, funds, resource's, etc., are available for the project.
Plans should be revised during completion of the work as necessary with approved changes.
There is a process for creating the most accurate estimate possible.
Padding is not an acceptable project management practice.
The project manager must meet any agreed-upon estimates.
Estimates must be reviewed when they received to see if they are reasonable and to check for padding and risks.
Estimates must be kept realistic through the life of the project by reestimating and reviewing them periodically.
Estimates can be decreased by reducing or eliminating risks.
Estimates can be decreased by reducing or eliminating risks.
A project manager has a professional responsibility to provide estimates that are as accurate as feasible and to maintain the integrity of those estimates throughout the life of the project.
439. The project cost and project schedule for work can be reliably estimated at the work package, or lowest, level of the WBS using bottom-up estimating, or at the highest level using top-down estimating.
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440. RAM is set based on WBS work packages level.
If the question states that you to put more weight on your most likely duration or cost estimate, this is another expression for PERT.
441. When you are answering formula questions you may not see the exact answer as one of the answer choices due to different types of calculators available and different rounding calculations. The most important thing to remember is that if you do not see the exact answer to the question, you want to select the closest answer to your calculated answer because this will be the
442. For the exam, it's important to know the formula for both triangular and beta distribution and understand that if you are being asked to calculate the activity (or cost) duration, you will need to read the situation carefully to determine which formula to use.
Look for language like simple or straight (triangular), or PERT or weighted (beta) that might help you choose the correct formula.
You may be asked to perform calculations using the formulas or to analyze information to determine how best to deal with a situation. The exercises that follow can help you prepare for three-point estimating questions on the exam. But first, here are the formulas again, plus a new one for standard deviation:
You must MEMORIZE these formulas and remember that they can be used for both time and cost estimates.
Legend: P = Pessimistic, M = Most Likely, 0 = Optimistic
Activity standard deviation is the possible range for the estimate. For example, an activity estimate of 30 hours that has a standard deviation of +/-2 could end up taking between 28 hours and 32 hours. We've listed the formula for beta activity standard deviation here. Although there is a standard deviation formula for triangular distribution, it's complicated and is unlikely to be on the exam. What you need to remember for the exam is that the greater the range created by the standard deviation calculation, the greater the risk.
The exam may ask you to calculate a range for an individual activity estimate using weighted (beta) averaging. To do you need to know the beta expected activity duration (EAD) and the beta activity standard deviation (SD). you calculate the range using beta EAD +/- SD. the start of the range is beta EAD- SD, and the end of the range is beta EAD+SD. the second exercise in this section will give a chance to practice these calculations. (be aware that it is possible to calculate a range for individual activity estimates using simple (triangular) averaging, which would involve triangular EAD and the standard deviation formula for triangular distribution. but again, since the exam is unlikely to require you to perform this calculation, we haven't included it in our discussion.)
If we are doing a project for the first time, and there is no previous history of similar projects to fall back on, it may make sense to use the Triangular distribution, as there is no basis to give more weight to a particular estimate. Thus, a Triangular Distribution is more suited for judgmental data estimates. These are most likely not based on a lot of experience or expertise… but are more of a guess-times.
Expected Activity
EXERCISE 1
Now tries this exercise. On the following charts, label the examples of each of the ten listed items by placing the item number next to be location on the chart(S).
Answers
Now tries this exercise. On the following charts, label the examples of each of the ten listed items by placing the item number next to be location on the chart(S).
Exercise 2
Calculate the expected activity duration using triangular distribution. It is best to calculate to three decimal places and round to two decimal places when you are ready to check your answers on the exam.
activity P M O expected activity duration
Complete the chart using the appropriate formulas. All estimates are in hours.
activity P M O expected activity
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Please compare the answers in the "Expected Activity Duration (Beta Distribution) column above to the answers in the "Expected Activity Duration (Triangular Distribution)" column from the previous exercise. Notice that the results are not hugely different. However, if you do not select the right formula for a question that requires the calculation of expected activity duration, you could end up picking the wrong answer.
443. Please note that these exercises are provided for understanding and do not necessarily represent the complexity of questions on the exam. Most of the questions on the exam relating to three-point estimating are relatively simple and may require assessment but not calculations.
Note that the formulas we've been discussing relate to activities, rather than the overall project, and that the exam concentrates on using three-point estimating to find ranges for activity duration and cost estimates. But as a project manager, you also use this information to calculate the overall project estimate and the project standard deviation to manage a project successfully. You need to consider how these ranges might affect the estimate of the overall project duration and cost. You can then use this knowledge to effectively address variations on your project.
For the exam, you should be able to do simple calculations using the formulas, understand that estimates of time (or cost) should be in a range, and know the concept of three-point time (or cost) weighted estimates per activity as well as how to calculate simple and weighted average distributions. You may also see a beta or PERT total project duration used in questions not requiring calculation (e.g., the project duration is 35 months plus or minus 3 months) and need to evaluate the situation to answer the questions correctly. Remember that, just like with an activity, the greater the range for the project as a whole, the greater the risk.
So why do project managers need to understand expected durations, range estimates, and standard deviations?
The main purpose is to use these concepts to better control projects. These calculations help you know the potential variances on your project and determine appropriate courses of action.
For example, you can use estimate ranges and standard deviation to assess risk. Looking back at the answers for the second exercise in this section, which activity has the most risks? The answer is activity B. It has the widest range and the highest standard deviation, and is therefore likely to have the greatest risk. These calculations are based on the pessimistic, optimistic, and most likely estimates for an activity the further away from the mean these estimates are, the more that could go right and wrong to affect.
The activity Therefore, you can assess and compare the risk of various activities by looking at activity ranges and standard deviations.
Don't forget that these concepts also apply to cost. Let's say you have estimated that a portion of your project will cost $1 million with a standard deviation of $200,000. You need to decide whether to use a fixed-price contract to outsource that piece of the project work. The standard deviation indicates there is a 40 percent range in the cost estimate for the work. Therefore, you would not likely choose a fixed-price contract, since this large standard deviation suggests there is not a firm definition of the scope of the work to be done. (See the Procurement Management chapter for information about different types of contracts.)
Make sure you have a general understanding of these estimating concepts. If you are still struggling with this topic, review this section again.
444. The easiest way to find the critical path is to identify all paths through the network and add the activity durations along each path. The path with the longest duration is the critical path. Be careful that you do the exercises that follow and practice doing this manual work for the exam. People will commonly not identify all of the paths or not calculate the duration correctly and get questions wrong on the exam.
445. "There is a start formula and a finish formula, and we always begin late:' Notice that the formula uses either two starts or two finishes and each begins with late.
start formula finish formula float = LS - ES float= LF - EF
You determine whether to use the start or finish formula based on the information available. For example, if an exam question states that you have a late start of 30, an early start of 18, and a late finish of 34, how do you find the float? Using the previous trick, you know to subtract the two starts or the two finishes. Since you do not have two finishes, you subtract 30 - 18 to get 12.
Using the Critical Path Method Now that we have discussed the basic concepts, let's look at how the critical path method works. We'll use the network diagram in figure 6. 7 as an example:
To determine the earliest and latest each activity can start and the earliest and latest each activity can be completed, you need to perform a forward and backward pass through the network diagram. The "early"
figures are found by calculating from the beginning of the project to the end of the project, following the dependencies in the network diagram-a forward pass through the network diagram. The "late" figures are found by moving from the end of the project, following the dependencies to the beginning of the project-a backward pass.
The first activity in the diagram normally has an early start of zero. Some people, however, use 1 as the early start of the first activity. There is no right way to start calculating through network diagrams for the early and late starts; either method will get you the right answer. Just pick one method, and use it consistently.
Let's start with the forward pass. You need to move through the activities from the start until you reach the end, determining the early starts and early finishes, as illustrated in figure 6.8 this example uses zero as the early start for the first activities.
It is important to look at where paths converge (path convergence). To compute the early start and the early finish in a forward pass, you have to take into account all the paths that lead into that activity (see activity F and activity Gin figure 6.8). The same concept applies to the backward pass; to compute the late finish and late start you need to consider all the paths that flow backward into an activity (see activity D and activity Fin figure 6.8). In this diagram, paths converge during the forward pass at activity F and at activity G. So you need to do the forward pass on both paths leading up to activity F, calculating the early finishes for activities D (EF = 4) and A (EF = 3). You then select the later early finish of activities D and A to use as the early start for activity F, since activity F cannot start until both activities D and A are complete. Therefore, the early start of activity F is 4. You use the same process for calculating the early finish of activities E (EF = 13) and F (EF = 12) before determining the early start of activity G (ES= 13).
Once you have completed the forward pass, you can begin the backward pass, computing the late finish and late start for each activity. The backward pass uses the duration of the critical path (in this case, 26) as the early finish of the last activity or activities in the network. See figure 6.9 for the late start and late finish data.
Again, you need to be careful at points of convergence as you move thought the network diagram There is convergence at activity F and at activity D. You work from the end back to these by first computing the late start of activities B(LS = 22) and G (LS=13). Select the earlier late start to use for the late finish of activity F, since activity F must be finished before either activity B or G can start.
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Therefore, the late finish of activity F is l3. this same process should be used on activities E (LS = 4) and F (LS=5) before calculating the late finish for activity D(LF=4).
Once you finish calculating the starts and finishes, you have the data required to calculate float. It's time to use those formulas. What was that trick again? "There is a start formula and a finish formula, and we always begin late." Therefore, the formulas are:
start formula finish formula float = LS - ES float= LF - EF
The activities with zero float are on the critical path (identified by the bold arrows). See figure 6.10 for the float of each activity:
The next few exercises should help you better understand these concepts. As you do the exercises, think about how knowing float helps you in managing your real-world projects.
Exam questions may be substantially similar to the following exercises, or they may be more situational and wordy, without requiring you to draw a network diagram. Be prepared for both types.
446. The following are good questions to test your knowledge about critical paths, float, etc.:
Can there be more than one critical path? Yes, you can have two, three, or many critical paths.
Do you want there to be? No; it increases risk.
Can a critical path change? Yes.
Can there be negative float? Yes; it means you are behind.
How much float does the critical path have? In planning, the critical path has zero total float.
During project executing, if an activity on the critical path is completed earlier or later than planned, the critical path may then have positive or negative float. Negative float on the critical path requires corrective actions or changes to the project to bring it back in line with the plan.
Does the network diagram change when the end dates changes? No, not automatically, but the project manager should investigate schedule compression options such as fast tracking and crashing the schedule to meet the new data. Then, with approved changes, the project manager should change the network diagram accordingly.
Would you have leaved the project with negative float? no; you would compress the schedule.
447. If you encounter multiple questions on the exam that require you to draw a network diagram you may be able to reuse the same network diagram to answer more than one question. Look to see if this is true before you spend time redrawing the diagram.
448. WARNING: For questions about changes to the network diagram, make sure you look for shifts to new critical paths caused by the changes to the network diagram or to activity durations.
Modeling PAGE 180In creating a finalized, realistic schedule, it is helpful to ask "What if a particular factor changed on the project? Would that produce a shorter schedule?" The assumptions for each activity can change and, therefore, the activity durations can also change. One of the ways to calculate, or model, the effect of these changes is through a Monte Carlo analysis.
449. Approximating number of work periods required to complete individual activities with estimated resources is done in Estimate Activity Duration process.
450. If you have two critical paths, the only right choice to affect the critical paths is by affecting the diversion
450. If you have two critical paths, the only right choice to affect the critical paths is by affecting the diversion