Critical Chain Method

Critical Chain Method allows buffers to be added due to limited or constraint in the resources and project uncertainties. Three kinds of buffers are used, project buffer, feeding buffer and resource buffer. Project buffer is added at the end of critical chain to avoid slippage in the project schedule or the customer committed date. Feeding buffer is added to the non-critical paths which are converging to the critical path. Resource buffer are used for flexibility.

Critical Chain Method is used in Develop Schedule process.

Critical Path Method

Critical Path Method is the longest duration path in a given network or the minimum time that is required to complete the project. This method is used to find the duration of the project. Here are the steps to find the critical path.

1. Draw the network diagram based on the dependencies of the activities.

2. Find the number of the paths from the network diagram. Number of paths means the paths which are traversing from start of the project to the end of the project.

3. Find the duration of each path by adding the duration of all the activities from the respective path.

4. The highest duration path is the critical path. And this itself is the duration of the project.

After finding the critical path one can find the total float or slack. Total float is nothing but how much an activity can be delayed without affecting the overall schedule of the project or the immediate start of the successor activity. How to calculate the total float? You need to follow two steps. One is forward pass and the second is backward pass. Forward pass is moving from start of the project by adding the duration of each of the activity and backward pass is moving from end of the project to the start of the project by subtracting the duration of each activity. After carrying out these steps you will find four values Early Start (ES), Early Finish (EF), Late Start (LS) and Late Finish (LF).

EF=ES + duration of the activity LS=LF - duration of the activity

Calculate total float using the formula

Total Float=LS-ES or LF-EF

The critical path activities will be always having zero total float whereas non critical path activities will be having float.

Critical Path method is used in Develop Schedule process.

Schedule Network Analysis

Schedule Network Analysis technique is used to develop schedule model. Under this we can use different technique like Critical Path, Critical Chain, resource optimization to calculate early start, early finish, late start and late finish activities.

Schedule Network Analysis is used under Develop Schedule process.

Reserve Analysis

During the estimation based on the uncertainties in the project one should park extra duration and or money which we call it as buffer. This is also called as reserves. There are two types of reserves: one is Contingency reserve and the second is Management reserve. Contingency reserve is based on “known unknown” and Management reserve is “unknown unknown”.

Contingency reserve can be derived based on quantitative risk analysis or based on standard deviation method or using organizational practices by putting some percentages.

Management reserve will be under management control and again this is derived based on unforeseen things which may happen to the project considering experience, historical data, contract terms and conditions, enterprise environmental factors, etc…

Reserve Analysis technique is used under the processes Estimate Activity Duration, Estimate Costs, Control Costs and Control Risks.

Three Point Estimating

To improve the estimation accuracy instead of considering only one value we can consider three values. This will cover most of the uncertainties. Three Point Estimating considers three values namely: Most likely or realistic value, Pessimistic or the worst value and Optimistic or the Best value. Depending on the distribution we use either of the below formula.

(P+4M+O)/6 which is Beta distribution or (P+M+O)/3 which is Triangular distribution.

Beta distribution is the weighted average which is also called as PERT (Program Evaluation and Review Technique).

Under the PERT one can derive the standard deviation and variance.Standard Deviation for an activity is (P-O)/6 and Variance is Standard deviation Square.

Three Point Estimating technique is used under the processes Estimate Activity Duration and Estimate Costs.

Parametric Estimating

Parametric Estimating is based on both historical data and the mathematical approach considering different variables. For example, 10 machines to be installed. To install one machine it takes one day. For 10 machines it may take approximately 10 days. One machine one day is the historical data and the calculation for 10 machines 10 days is mathematical model. So here we are considering both historical and mathematical approach unlike Analogous estimating where we consider only historical data. This technique provides higher level of accuracy.

Parametric Estimating technique is used under processes Estimate Activity Duration, Estimate Costs processes.

Analogous Estimating

Analogous Estimating technique is used for estimating duration, cost based on the previous similar projects data which is historical data. The word analogy means history. Even though this technique is less accurate, it is less time consuming and less costly.

Analogous Estimating technique is used under processes Estimate Activity Duration, Estimate Costs processes.