Lead, lag and CPM

The big idea

According to PMI a project is a temporary effort to create a value, by changing the status quo. It has an start date and an end date. In between them are some great pillars on which the project relies. One of those is the scheduling or planning management [1]. While scheduling can be done with various tools and methods, this article will focus the use of lag & lead both for scheduling and for purposes as Key Performance Indicators (KPI). As the purpose of this article is to investigate and show how scheduling could be optimized for project efficiency, some complementary methods will be included. These methods will be Critical Path Management (CPM) and Program(Project) Evaluation and Review Technique (PERT) to get a quantified take on possible scheduling risks that might be faced.

As a project consists of different activities that make up the change of status quo, these activities might be connected and some independent. Nevertheless, do we need to face which kind of interaction these tasks have in order to optimize the time schedule of the project.

When using lag & lead, the project activities will most often be sequenced. To get a understanding of the sequence, the precedence relations of the activities should be mapped. This could be done by the use of CPM-, PERT-, and network diagrams. The PERT and CPM holds some more data and assumptions which will be discussed later. Those can be seen as iterations of the more simpler version, namely the network diagram that shows the precedence relation between actions (sæt springer kilde ind, side 18). For the purpose of this article, the precedence network will form the basis (indsæt evt. kilde der samler op på PMBOK).

Research in scheduling has grown ever since its start in the late 1950’s. CPM and PERT being the main focus back then, means that they have undergone severe development. As a consequence further theories and iterations have been based on mathematics (springer preface). To grasp the concept of lag & lead, the computerized methods developed should be to far over the aim for this article.

Scheduling

As a first do the project manager need to realize whether the project is approached as predictive (waterfall) or adaptive (PMBOK 7th s. 58). This should not be confused with the development approach which is also described with these terms in PMBOK (PMBOK 7th s. 35).

To choose the best approach, the project manager should acknowledge how much information there is to be found about the project. If the project consist of already known activities, workload and required skills the predictive would certainly be the best choice. On the other hand, would the adaptive approach be more appropriate if the tasks and workload is unknown or could change through the project. This approach is iterative and are supplying the project with beneficial insights. To this day is the most used approach the predictive (sæt kilde ind, gantt, cpm etc.). Therefore, the predictive approach will be examined mostly in this article. However, it will touch the adaptive as well.

For the predictive approach the following steps should be considered according to PMI (PMBOK 7th edition):

1. Create specific project activities based on the scope.
2. Sequence the activities (find precedence relations).
3. Estimate the different resources needed for each activity (i.e. time, people, physical resources).
4. Allocating people to the activities.
5. Adjust the above to an schedule can be agreed.

It sometimes happen that the schedule does not meet the delivery date and duration first agreed. To address the issue of delaying the project, compression methods could be applied. This could be done by crashing or fast tracking for instance. By shortening the duration of activities by adding workers or working overtime, crashing is applied directly to a specific activity, thus decreasing the duration. Another alternative would be the fast tracking method which is compressing by the use of lag & lead (PMBOK 7th s. 59).

When using fast track, activities that normally would be sequenced will be done partially in parallel.

To use the lag & lead tool the whole schedule should be made, the tasks identified (such as resources and duration) as well as their logical relationship between them. The project management team needs an great overview of the tasks that should be done in the project. All tasks such as work packages and activities should be listed roughly(https://project-management.info/project-schedule-baseline/):