The Critical Path

15 April, 2014 12:00PM · 9 minute read

Many people bandy-around the expression “The Critical Path” but what does it really mean and how is it useful? The truth is that it’s a part of “Project Management” and this phrase carries negative connotations for a lot of people but it’s a tool to help us get to where we need to be.

Project Management is an often hated discipline for a litany of really good reasons but the reality is that it’s a very broad topic. According to WikiPedia “Project management is the process and activity of planning, organising, motivating and controlling resources, procedures and protocols to achieve specific goals." Most people don’t realise that what every person does every single day is a form of project management. If you need get some Monroe Apples before the kids get home then there’s a list of activities you might need to perform in order to complete that task: a list of sub-tasks that need to be performed in order to achieve that result. Most people will either consciously or subconsciously perform any one or most of those tasks without stopping to think about the details too much. That’s fine if your goal is to fill up a fruit bowl whose biggest repercussion if you don’t fill it up are cranky kids getting home from school or you just have to choose something else to eat.

There’s three (maybe four) conditions that dictate when you need to project plan in a conscious and structured way:

Now the decision has been made to structure our tasks, the method/tool that’s most popular in the world today is by far the Gantt Chart.

Gantt Charts

Developed by Henry Gantt in the 1910s it’s a project planning tool that displays tasks on a linear X-Axis with respect to time. It’s evolved to include resource allocations and few other features as well but mostly unchanged from its original design over 100 years ago. A little known fact about the Gantt chart is that a Polish gentleman by the name of Karol Adamiecki in 1896 developed the “Harmonogram” through his work operating a steel mill however it wasn’t published widely until 1931 and translated into English but Gantt is credited as the original inventor. These days there’s a lot of software around that can produce Gantt charts including Microsoft Project which is now called Project Professional 2013. The more serious software package used in Construction Projects I’ve been involved with is made by Oracle and is called Primavera and it’s current version is usually what it goes by: “P6”

There are several free versions out there as well such as Gantt Project for Mac.

The concept is simple enough: make a list of all of the tasks and sub-tasks then assign durations to each one of them. After that connect each task to each other task upon which it depends (dependencies) and then there’s a map of all of the tasks and how they interrelate to help illustrate what needs to happen by when. Using the earlier example such that our final deliverable milestone will be 6 Apples in the fruit bowl by 4:00pm as the kids are going to be home by 4:00pm. Now that there’s a deadline we set the starting time at 11:00am.

For this example our task breakdown is as follows:

The sequence of driving may or may not matter but the car won’t make it home without stopping at the gas station. As forward-planning is the name of the game we’re going to opt to do that first. Also to ensure we’re not cranky when the kids get home it’s important to consume a museli bar at some point during the time allotted in order to stave-off hunger. Noting that we don’t technically have to empty the fruit bowl of the manky old fruit until we show up with the fresh Apples, still choose to forward-plan and do that first. The rest of the activities are essentially sequential. Using the free Gantt Project mentioned previously the final Gantt chart GAN format illustrates the float for emptying out the fruit bowl and for eating the museli bar and final dependancies. Note that using the example and that most project planning tools work in whole days of effort, it’s not possible to break down the tasks to real-life durations hence each activity is set to take ‘1 day’ on the chart and they’re all the same length. Alas.

PERT Charts

Project Evaluation and Review Technique (PERT) Developed in the 1957 by the United States Navy. A PERT resembles a state transition diagram with tasks referred to as ‘Nodes’ and each node contains the information about that task: Name, expected (normal) duration, early start time (ES), early finish time (EF), late start time (LS), late finish time (LF) and the crowd favourite: Slack - also known as Float. Each of the tasks is connected to each of its dependent tasks and ends up looking a bit like a web. Most of those items are self-explanatory however the last one isn’t so much. The idea centers around task concurrency whereby if a task must be completed by the end milestone but can be conducted in parallel to another set of tasks, and that task takes less time to complete then its absolute start date can “float” earlier or later in time and still meet the final deadline. Float is meaningless in a single path PERT or Gantt for that matter.

It’s not uncommon for people to prepare PERTs in convention drawing tools that are cheaper/more readily available such as Visio however both Project and Primavera have PERT analysis tools included in them. The original PERT used “activity on arrow” methodologies that placed detail about durations on the transitions between the nodes however this has fallen out of favour and now “activity on node” is the most common form of PERT. {The last PERT I was involved in was back at Nortel in 1997 and I haven’t come across them used in any projects in Australia. Doesn’t mean they aren’t used just haven’t seen them. 100 years on Gantt is still king. I’m not going to talk any more about PERTs but they are interesting if you want to know more check out the show notes.}

The Critical Path Method

You may be thinking: thanks for the high level crash course in project management but what the heck does this have to do with A CRITICAL PATH?? It’s often used as an expression:

Like all good expressions that encapsulate a good idea they tend to get overused, usually by people that don’t really understand them, which then devalues the expression overall such that when they are used in the correct context people tend to roll their eyes and go “buzzword bingo!” Two other examples of similar expressions recently that grew tiresome include “Proactive” and “Disruption”. The correct usage from a historical perspective is The Critical Path Method and the method was developed in the late 1950s by Morgan Walker from DuPont and James Kelley Jr. of Remington Rand. It appeared around the same time as PERT. Another little known fact is that the early form of the Critical Path Method was used and partly attributed to the success of the Manhattan Project in the second world war.

Essentially the method is the idea of mapping the path between the longest paths between tasks to the end deliverable/milestone, and the earliest and latest that each activity can start and finish without making the project any longer. It’s not so much the path but the idea of iteration that matters. Once a project is planned are there ways to add addition personnel to execute paths in parallel for example? In our Apple quest example assume that we have a helpful friend living in the house and they are able to assist. By increasing the number of people it’s possible to perform more activities concurrently. Hence whilst person A is getting dressed person B is finding the keys and starting the car in parallel. In addition when person A is out procuring the Apples person B can empty the fruit bowl. This has reduced the overall project schedule by 2/7ths of the total duration and changed the critical path. On the Gantt chart from earlier the greyed out boxes indicate the critical path of tasks. On many tools red is used to highlight the critical path. This process of adding resources is often referred to as “Fast Tracking”.

Being A Useful Project Manager

There are two big issues (although there are many more than that in total) with effective Project Management and so often drive negative behaviours and responses in people affected by a schedule or a timeline. This then leads to a mistrust or lack of faith and belief in the usefulness of schedules, PERTs and Gantt Charts and their associated project managers:

The biggest problem with project management is the disconnect between most PMs and what it is they’re managing. In construction projects there have been numerous occurrences where the PM does not appreciate the difficulties with software development as they have experience in civil construction and once the concrete is set, you don’t break it up and try again. Iteration is unheard of unless there are major dramas and that leads to bad scheduling, bad planning and a bad end result. Another issue with the “throw more people at it” fast-tracking mentality is that there are genuinely activities that can not be completed any more quickly. My favourite example of this is the idea from the software-famous Mythical Man-Month book and is sometimes referred to as Brookes Law where the Author Frederick Brooks states: “Nine women can’t make a baby in one month.” It’s a beautifully simple way to illustrate the problem that not all tasks can be fast-tracked.

The other major problem is that schedule for some PMs ceases to be about planning for the future and becomes a negotiation tool for applying more pressure to those performing the tasks in question. Rather than helping that ends up hindering the project completion and builds animosity. Ultimately Gantts, PERTs and applying the Critical Path Method are all tools to help understand the best way to plan activities to get the end result in a known period of time. Just like any tool they can be abused if incorrectly wielded so proceed with caution or the wrong conclusion will inevitably result.