Techniques for Deciding Duration of Activites

Interesting subject. There is no real or special technique for deciding duration of an activity, only a lot of common sense.

To decide or to define the duration of an activity, you need to consider the following factors:

1st - Production rates and the resources availability in the market. (The level of skill will vary from one country to another.)

2nd - The quantity of work involved on a given task.

3rd - Space ( i.e. Is there enough space to put 30 men to work in the same area)

4th - Time ( Working hours per day)

Knowing all these factors, you can inteligently decide and predict the duration of a given task. Not easy when you are working on a big project with thousands of activities.

Actually for most activities durations shall be calculated by PM software and not entered manually.
Duration shall be calculated basing on activity type, quantity of work to be done (activity volume), assigned resource types and quantities, and resource assignment productivity norms (production rates).
Resources can be assigned manually or chosen by the software if project planner assigned not individual resources but resource skills. In the last case activity duration can be calculated only in the levelling process because resources may have the same skills but different productivities.

don’t forget the location and the conditions! is the Project in Iraq? is it under water or in the middle of the desert? Determining durations of activities is like betting in a lottery!

Other factors you need to consider:

Is the programme time driven or resource driven.

There are some projects (i.e. offshore projects) which are resource driven, it means you have limited resources usually based on the number of beds or accommodation they can provide offshore. In this case, the duration will be dictated by the number of resources you have.

On the other hand, Time driven programme means you have unlimited number of resources and the only constraint is space. You can breakdown the task into multiple activities and assign multiple resources or gangs to complete the task given. However, there are some task which are progressive in nature. It means only one gang can be assigned to complete the task progressing from one end to the other.(i.e. Roofing).

Cheers,
Daniel

Talk to the people who have experience of doing the work, talk to the estimator on the job and always have an updated OBS of the available resource.

How about taking 3 of your estimates and doing a simple PERT analysis on them.

See This >>> PERT description.

This is essentially the basis for Monte Carlo analysis, but you can use it as a tie breaker on individual estimates for a specific activity

Andy

The Link mentioned for PERT is not working.

Thats only description of theoretical stuff or its a technical paper.

Will u plz post it again.

Thanks,

Hi guyz,

Check this classic method.comments are awaited;

Duration required = Total mandays required/ men per day

Total mandays = Total quantity/production rate

Men per day should be determined from the following two conditions;
1. Space restriction
2. Overall time restriction

Thanks,

Hi Guys,

I’ve played around with the link that Andy supplied to PERT information, and I think the link below takes us to the information he found.

PERT link

Regards

Chris Oggham

That’s the one thanks Chris.

Andy

Simply, as stated previously,
Duration required = Total mandays required/ men per day

Total mandays = Total quantity/production rate