Download Critical Path Analysis and more Study notes Project Management in PDF only on Docsity!
Networks, Gantt charts and Critical Paths
- Robin Beaumont Date: 18/12/2001 14: Networks, Gantt charts and Critical Paths
- LEARNING OUTCOMES CHECK LIST FOR THE SESSION Contents
- INTRODUCTION.............................................................................................................................
- THE GANTT CHART......................................................................................................................
- MAIN PROJECT PHASES..............................................................................................................
- ACTIVITIES AND EVENTS...........................................................................................................
- NETWORK DIAGRAMS
- 6.1 EVENT NUMBERING
- 6.2 A DDITIONAL EXERCISES
- TIME CONSIDERATIONS.............................................................................................................
- 7.1 ESTIMATING
- 7.2 EXTERNAL DEPENDENCIES AND Q UALITY ISSUES
- 7.3 A NNOTATING N ETWORK DIAGRAMS
- 7.4 EARLIEST TIME (E) /F ORWARD PASS AND P ROJECT DURATION
- 7.5 LATEST TIME (L) /BACKWARD PASS AND THE CRITICAL P ATH
- 7.6 O BTAINING A CRITICAL PATH IN MICROSOFT P ROJECT98...........................................................
- NETWORK DIAGRAMS IN MICROSOFT PROJECT98........................................................
- SLACK AND FLOAT.....................................................................................................................
- RESOURCE ANALYSIS
- NOW CHECK WHAT YOU HAVE LEARNT........................................................................
- ADDITIONAL OPTIONAL EXERCISES
- REFERENCES
- MCQS...........................................................................................................................................
Networks, Gantt charts and Critical Paths
1. Learning outcomes check list for the session
Each of the sessions aims to provide you with both skills (the 'be able to's' below) and useful information (the 'understand what's' below) listed below. After you have completed this session you should come back to these points ticking off those you feel happy with.
Learning outcome Tick box
Be able to describe a Gantt chart!
Be able to describe the purpose of a Gantt chart q!
Be able to describe a Network diagram!
Be able to describe the purpose of a Network diagram!
Be aware of the 4 overall aims of Project management as espoused by the PRINCE method
Be able to provide examples of events!
Be able to provide examples of activities!
List the difference between event and activity centred network diagrams
Be able to develop a Network diagram from a list of activities!
Describe the purpose of event numbering in Network diagrams!
Be aware of the PERT method of activity duration estimation!
Describe the traditional method of activity duration estimation along with its dangers
Be aware of the importance of considering external constraints!
Be able to modify Network diagrams to show the activity duration's.
Describe, and be able to carry out the process of Forward Pass!
Describe what Earliest time (E) is along with its relationship to Project duration
Describe what Latest time (L) is!
Describe, and be able to carry out the process of Backward Pass!
Describe what a Critical Path (CP) is!
Describe what Critical Path Analysis (CPA) is!
Describe the various types of “periods of inactivity”!
Describe how periods of inactivity can be manipulated!
Be aware of resource issues!
Back to top of the document
Networks, Gantt charts and Critical Paths
4. Main project phases
There are hundreds of project management techniques around supporting a host of 'consultants', and while each technique purports to offer some additional benefit over rivals little empirical research has taken place. The lack of empirical findings has not prevented the development of various standards such as ISO 9001 (International Standards Organisation) and BS5750 (British Standard). Within these standards specific project management methods have developed such as that of PRINCE (Projects in Controlled Environments). Such methods have been designed for large projects and are often too unwieldy to be downsized. However, some of PRINCE's principles are worth bearing in mind:
The overall aim of project management, according to the PRINCE method, is to:
- Deliver required products
- Deliver specified quality
- Deliver on time
- Deliver within budget (resource constraint)
PRINCE expects you to be able to define the products ('deliverables') at the start of the project in a document known as the PID (Project Initiation Document). Although this is often very difficult in the research environment where investigation is the prime activity one should not forget the poor researcher of a TV programme who is given a defined deliverable in a specified time. Possibly the variable quality of the outcome in this situation demonstrates the dangers of such an approach! In the research setting it is possible to define deliverables but these are frequently re-defined or developed during the project. Creativity and project management often make uncomfortable bed fellows.
PRINCE has three main aspects:
- Organisation - A project board and Project site office (PSO) consisting of people with set responsibilities.
- Plans - Various plans specifying technical, resourcing, quality and exception issues.
- Controls - These are of two types; Managerial controls assess progress throughout the project with various defined assessment and checkpoint (actual versus planned achievements) meetings. The other type of control concerns the product ('deliverables').
Port folio Exercise:
Considering the organisation, plans and controls issues of PRINCE how might they be relevant when planning a research project investigating the quality of nursing care patients receive in three local hospitals? This should be no longer then one page of A4.
Back to top of the document
Networks, Gantt charts and Critical Paths
5. Activities and events
At the most basic level a project consists of a series of activities and events.
Different management methods place more emphasis on one of these aspects. An example should help. Consider the project of installing a new bathroom sink (referred to as the 'sink' project from now on) which can be viewed either as a series of activities or events:
Activity (task)\perspective
Event perspective
Decorate ceiling Finish decorating ceiling Tile area Area tiled Install basin / taps Basin / taps installed Obtain basin/taps Basin/taps obtained Obtain tiles Tiles obtained
From the above it can be seen that an activity usually results in at least one event so the two perspectives are in reality related. One perspective emphases the process while the other concentrations more on the outcome. In reality a good project manager controls both aspects. It is usual at the start of a project to decide which perspective will be used. Microsoft project software expects a series of activities ('tasks') and I feel that the activity perspective is the most intuitive, at least for the people actually undertaking the project.
Key point:
Create a list of activities (or events) when starting to define a project.
Port folio Exercise:
Think of a small project (i.e. less than 15 activities) and list the activities you would need to undertake. Such a project might be moving wards, establishing a new service, producing a article or book chapter for publication or planning a local community health event.
This should be no longer then one page of A4.
Back to top of the document
Once you have the list of activities in tabular format (i.e. as above) you can begin to sort them into a logical order of some type. You can also depict them graphically such as in a network diagram:
Activity perspective Event perspective (precedence diagram)
The next section will look in more detail at the type of network diagram that uses the activity perspective.
Back to top of the document
Decorate ceiling start decorate ceiling
finished decorating ceiling
Networks, Gantt charts and Critical Paths
6.2 Additional exercises
- Draw a Network diagram for 'sending a letter' including the following activites:
Write letter Put in envelope Address letter Place stamp on letter Post letter
- Draw a Network diagram for ' Writing a research paper', including the following activities:
Agree subject area with supervisor Review literature Prepare section headings Prepare first draft Initial discussion of first draft with supervisor E-mail first draft for internal peer review Collate e-mailed comments Prepare final draft Discuss final draft with supervisor Prepare final version Disseminate Review comments on final version Present findings
- Draw a Network diagram for 'putting on a half day seminar'.
- Draw a Network diagram for your career development in the next five years
Back to top of the document
Networks, Gantt charts and Critical Paths
7. Time considerations
The network diagram above says nothing about the actual time the project will take, only the sequence of activities and events. The first stage in considering the duration of the project is to obtain an estimate for each activity.
7.1 Estimating
While it is usual to provide a single estimate for each activity a method called PERT (Program Evaluation and Review Technique) demands you supply three estimates for each activity:
- Quickest reasonable time
- Most likely time
- Worst time
The actual estimate for each activity is then taken to be:
=(Worst + 4(Most likely) + Quickest)/ This may seem unnecessary overkill (the PERT technique was used to develop the Polaris missile) but it may be particularly pertinent in the academic environment where the duration is often taken to be the quickest rather than the most likely! Because external dependencies are rarely considered the 'worst time' is not even thought of. Microsoft Project98 allows you to enter these three types of estimate as well as the more traditional single one.
Port folio exercise
Consider four activities you have identified for your exercise and calculate their duration using the PERT method. What problems, if any do you see using it? Keep your work in your portfolio
Back to top of the document
7.2 External dependencies and Quality issues
Project managers often advise those making time estimates to simply double any initial figure they come up with! This may seen rather radical but if one considers that project activities often have unseen external dependencies which can have dire consequences it is not too far from the truth. For example in the 'basin' project each activity depends upon a supplier being able to provide the required materials. Also the desired level of quality has an affect on activity duration, for example the taps I want (they are manufactured by a company with my surname which engraved on the tops) are only available in Brighton necessitating a visit for closer inspection. Another aphorism goes something like 50% effort for 90% of the quality. You must always ask yourself if the small increase in quality is worth the disproportionate effort?
Port Folio Exercise:
For the small project you chose in the previous exercise list the external dependencies for each activity. Rate the degree of risk (none, low medium, high) these might have on the duration of each activity.
Despite the difficulty in obtaining realistic duration estimates they are essential as the overall project duration is dependent upon them.
Back to top of the document
Networks, Gantt charts and Critical Paths This is also the general rule: If you obtain more than one 'Earliest time' value for an event choose the highest.
The corrected network diagram is given below.
1 10
decorate ceiling 2 40
obtain tiles 4
install basin/taps 4
E= 0 + 2 = 2 E= 2 + 4 = 6
warning: still called 'earliest time' although highest value chosen
E=12+4=
E=2+10=
obtain basin /taps 10
30 tile area 2
20
E= 0
The project duration is therefore 16 weeks! Not 6 days as I had originally thought.
Port folio Exercise: For the small project you chose annotate the network diagram to work out the project duration.
Back to top of the document
7.5 Latest time (L) /Backward pass and the Critical Path
In the previous section the project duration was calculated, and in doing so took into account points where some activities where idle ('Floating') in other words waiting for another activity to complete before being able to move on. By moving backward over the various activities from the project finish event (i.e. Backword pass) we are able to determine a path of activities/events that contain no idle periods (Float/Slack). Such a path is called the Critical path. As none of the activities have any leeway on the critical path it is said to be 'critical' in terms of project management because it is important that each activity starts and ends as scheduled along it. Backward pass involves calculating the Latest time (L) for each event. This is done in much the same way as calculating the Earliest time in the previous section:
- Working backward from the finish event make the 'latest event time equal the project duration.
- The 'latest time (L)' for an event is the 'latest time' of the succeeding event minus the corresponding duration.
- If there appear to be two or more 'latest times', choose the lowest.
- Mark the critical path in some way (e.g. in red as Microsoft project does or double line
through each arrow ( lI )as below
The above process is shown in the network diagram below:
decorate ceiling 2
E= 16 = obtain tiles 4
install basin/taps 4
tile area 2
obtain basin /taps 10
1 10 20 30
L=12-2=10 L=16-4=
L=12-(2+4)= L=2-2=0 L=12-10=
warning: still called 'latest time' although lowest value chosen
40
Port folio Exercise: For the small project you chose annotate the network diagram to show the critical path.
Networks, Gantt charts and Critical Paths
The events that occur along the critical path are referred to as milestones, and much management effort is put into ensuring project milestones are achieved on time. Note that in Microsoft Project the term milestone has a different meaning. A quick way of checking to see if you have identified the critical path correctly is to verify that all the Earliest and Latest times on the critical path are identical (no slack).
The process of obtaining a Critical Path is called Critical Path Analysis (CPA). Not to be confused with other meanings for CPA such as the Care Programme Approach in Psychiatry.
7.6 Obtaining a critical path in Microsoft Project
Microsoft project provides a number of very easy ways of obtaining a critical path for a project. Once you have drawn a Gantt chart in Microsoft project, click on the Ganttchartwizard icon and at step two when you are asked 'what type of information do you want' click the 'critical path' option. Alternatively you can click on the menu option ->view -> 'tracking Gantt' option. This is set-up to show the critical path in red. If all you want to see is the critical path you can choose the menu option -> Project -> filter for -> Critical.
Optional port folio exercise This is an optional exercise for those of you who have a copy of a piece of project management software: For the small project you chose use the software you have to show the critical path. Keep your work in your portfolio.
8. Network diagrams in Microsoft Project
While Microsoft Project demands that you use the Gantt chart to enter the initial project specification it does provide a number of other charting options. The nearest to the Network diagram provided is the PERT chart which unfortunately is event rather than activity orientated. The 'PERT chart' output for the 'basin' project is given below.
Optional port folio exercise This is an optional exercise for those of you who have a copy of a piece of project management software: For the small project you chose use the software you have to create a PERT or Network diagram. Keep your work in your portfolio
Networks, Gantt charts and Critical Paths
Microsoft Project98 allows the user to provide all the dates discussed above. It also automatically calculates the free and total slack(float). Here are the entries for the 'tile area' activity:
Free slack(float)
Early start Start (scheduled)
Late start Early finish Finish (scheduled)
Late finish
4 wks 14/02/00 Mon 14/02/00 Mon 13/03/00 Fri 25/02/00 Fri 25/02/00 Fri 24/03/
Back to top of the document
In Microsoft Project98 when you enter the start and end dates for an activity (called the scheduled dates) the same values are also set for the 'Early start' and 'Early finish' dates respectively. Microsoft Project98 assumes you want everything to happen as soon as possible!
Port folio Exercise:
For the small project you chose annotate the network diagram to show the total slack, free slack, and head slack for each activity.
While most of the above information is provided chiefly for reference purposes a basic understanding of slack/float is useful allowing you to be more flexible and creative with project plans. The periods of inactivity can be manipulated by:
Lengthening the activity period thereby reducing the resource intensity. Moving, to possibly make more appropriate use of a resource shared between several activities.
Back to top of the document
10. Resource analysis
For industrial projects resource management is of key importance. Put simply the greater the resource input the quicker the job gets done provided the input is of a comparable quality. Because it is often easy to obtain casual labour at low rates in this situation and reduction in time (e.g as in building a new store) is essential to optimise profits projects are devised to take the least time with the greatest resources available.
Unfortunately in academia and other specialist areas there is not a large one, if one exists at all, pool of casual expertise that can be utilised and in reality there is frequently only one source of each type of expertise. In such a situation resourcing in not considered as the pragmatics of the situation mean that 'the individual' just works harder and longer hours within the alloted time to get the work done. A very unsatisfactory situation.
Because resource analysis is a separate issue with a distinct set of techniques it is not possible to discuss it in the time we have to complete this module. In this handout I have assumed that the project that have been presented would be undertake by a single individual.
11. Now check what you have learnt
Now read through the 'Learning outcomes check list' again. How many can you tick? If you are not sure about any particular item get the person beside you to explain or ask / e-mail me.
Networks, Gantt charts and Critical Paths
12. Additional optional exercises
- Set up a discussion board thread about Project management to discover:
- What people found difficult to understand in this section
- What was missing
- If anyone has used these techniques in the real world discover what they thought of them
- Ask various administrators at your place of work if you may have a look at some past or present project plans. See how they conform to the techniques described in this section.
13. References
Argyle M 1989 (2nd ed.) The social psychology of work Penguin
Field M Keller L 1998 Project management. Thomson learning & the Open University see www.thomsonlearning.co.uk
Gilb T 1988 Principles of software engineering management. Addison-Wesley
Karasek R Theorell T 1990 Healthy Work: Stress, productivity and the rconstruction of working life. Basic Books
Lang D W 1977 (2nd ed.) Critical path analysis. Teach yourself books - Hodder & Stoughton
14. MCQs
The following Multiple choice questions have been designed to see if you have read through the material carefully.
- Which of the following software packages provides support for project management? a. Powerpoint b. Access c. Paradox d. Microsoft project
- In a Gantt chart which of the following statements are true (there may be more than one)? a. The top of the chart displays who's responsible for each task b. The activities within the project are shown as a series of rectangles c. You can explode activities to define sub-activities d. You can choose from a wide range of time periods to specify the project e. Tasks are listed vertically f. Tasks also have a unique number attached to them automatically by Project
- PRINCE stands for: a. Projects in Clinical Environments b. Projections, Requirements in Clinical Environments c. Projects in Controlled Environments d. People Responding in a Controlled Environment
Networks, Gantt charts and Critical Paths
- Using the PERT method of estimating activity duration involves: a. Finding the quickest reasonable time, most likely time and worst time and adding them together b. Finding the most likely time and worst time, multiplying this value by 4 and then dividing it by 2 c. Finding the quickest reasonable time, most likely time and multiplying this value by 4. Then adding the worst time and dividing this value by 6 d. Finding the quickest reasonable time, most likely time and multiplying this value by 6. Then adding the worst time and dividing this value by 4
- Which of the following pairs of factors, according to the notes, have the most affect upon activity duration: a. External dependencies and resourcing issues b. External dependencies and cost issues c. External dependencies and quality issues d. Quality issues and resourcing issues
- Project duration is calculated by: a. Using the method of backward pass b. Is the summation of earliest event times c. Is the summation of earliest event time except when there are two calculated for a particular activity when the smallest Earliest time value is accepted. d. Is the summation of earliest event time except when there are two calculated for a particular activity when the greatest Earliest time value is accepted.
- The Critical Path is: a. The chain of activities through the Network diagram which includes the greatest slack b. The chain of activities through the Network diagram which includes the least slack c. The chain of activities through the Network diagram which includes as many different activities as possible
Networks, Gantt charts and Critical Paths
- Please complete the table below indicating which label goes with each MCQ option (note that a MCQ option may be used for more than one diagram label): a. Independent float b. Fee float c. Total float d. Scheduled start / end dates e. Tail slack f. Head slack g. Head float Diagram Label MCQ Option
1 2 3 4 5 6
Document management information:
Source: C:\edinburgh\mod8\sect5\cpa\word\cpa1.doc
Base document: Word 2000 converted to pdf (ver 5)
Date / Time: 18/12/2001 14:
