Man, how come nuhbody doan nevah tek muh serious?

Fraternally in project management,

Steve the Bajan

Great rule of dumb.

The correct number of critical path activities in a project varies a little according to the type of project. In a pharmaceutical development project, for instance, the potential impact of poor quality on patients' lives means that not more than 6.67% of activities should be on the critical path. (NOTE: this does NOT mean 6.66667% -- it means EXACTLY 6.67000%!).   In nuclear power outages, it depends on the type of plant: boiling water plant outages should have 7.74% of the activities on the critical path, while pressurized water plants should be at 8.41%. 

In a construction project, 5.93% of activities should normally be on the critical path. However, this can change depending on the climate where the work is being done:

• For every three days that the humidity rises to more than 84%, the number of critical path activities MUST be reduced by three activities, and
• For every five days that the humidity never rises above 50% AND the average cloud cover is greater than 35.7%, the number of critical path activities MUST be increased by four. 

This can sometimes cause slight difficulties: some work may have to be added if there are a lot of cloudy days with low humidity, and this can result in law suits to determine whether the customer or the contractor should pay for the additional work. (In the most recent case in Tortola, the court ruled that the most prominent meteorologist located within a fifty kilometer radius should pay for the extra work, a decision that is, however, being appealed.)

Perhaps the most knotty problem that can be caused by a climate-driven change in the required number of critical path activities is when a roof has to be omitted from a building in order to reduce the number of CP activities.  As a result, it is often a good idea to plan for an additional and separate roof on an outbuilding, such as a garage. Thus when required, the garage roof could be left out (although it obviously depends on circumstances -- if there are severe budgetary constraints, it would cut costs more to complete the garage roof and omit the roof for the main building. This is where the art of project management comes in!)

In software projects utilizing agile methodologies, it is regarded as mandatory that not less than 105% of activities (to allow for re-work) be on the critical path.

Hope this helps.

Fraternally in project mangement,

Steve the Bajan

just want to highlight what Dan wrote as follows:

"Whichever Schedule Network Analysis Technique you are going to use, you must work off of the Project Scope Statement,as approved by your Sponsor,Owner ,in the Project Charter or Contract. My opinion is to make sure the Sope Statement(s) are written with the utmost care,with input from your Key Stakeholders and that the Whole Project Team has committed,'Buy In' is the Most Critical of Any Path to Successful Project Completion".

Any Project cannot be done without resources, so I supposed for now, "Floats" and "Critical Path" derived from schedules or programs that were not resource loaded are meaningless (obsolete).

"Resource Critical Path" and "Resource Floats" - would be the future!

The use of artificial constraints or unnecessary logic to create or reduce the number of critical activities in a Time Analysed schedule is to be avoided.

However, a good heuristic is once the schedule has more then 20% of critical activities the probability of it completing within the planned duration is very low.

As soon as you resource schedule/level there can be no concept of float. Move any activity and you need to reschedule to re-balance resource demands.

There is a collection of papers on our scheduling page at http://www.mosaicprojects.com.au/Planning.html#Roles that discuss good scheduling practice.

Hi Lizz,

Interesting questions! Is this a quizz? Anyway, since i am not busy at the moment, i might as well answer your questions.

We normally do this exercise "resource scheduling" to optimize usage of resources and of course this will translate to $$$ at the ned of the day. As you know, in construction everything is dependent on resources (cash, labour, materials & equipment) to complete a task and if you are on the contractor's side then it is in your best interest to perform such excercise.  If you have limited resources then the programme will become resource driven and this will (of course) affect overall progress.

Your 2nd question, First of all you need to define what you consider critical, it may range from 14 days to 0 days. Normally activities becomes critical because they are tied to a key date, completion date or an interface date defined in the contract. Contract key dates normally have penalties attached with them in the  form of liquidated damages or general damages (that is if you fail to meet this important key dates).

An activity or a series of activities can become critical when the total float is less than what you consider critical.

Best regards,

Daniel