Upcoming SlideShare
×

# Project Duration Estimation

591 views

Published on

Project Duration Estimation
explained every technique

Published in: Engineering
• Full Name
Comment goes here.

Are you sure you want to Yes No
• Be the first to comment

• Be the first to like this

### Project Duration Estimation

1. 1. Page 1 of 16 Software Project Planning and Management (CAP 590) Term Paper: - Project Duration Estimation Synopsis By: - Harsh Behl Submitted To- Sahil Rampal 11100961 RD1102A27 Date: - 07 April 2014
2. 2. Page 2 of 16 Index Page no 1. Introduction 3 2. Technique’s Which Are 4 Used to Estimate Project Duration 3.Top Down Approach 4-5 4.Bottom Down Approach 5-7 5. Expert Judgments 7 6.Historical comparison 7 7.Functional Points 7-8 8.Object points 8-10 9.CPM (Critical path method) 10-12 10. Pert 12-15 11. Conclusion 15 12. Bibliography 16
3. 3. Page 3 of 16 Introduction As we all know that estimating the activity duration is very important to the success of any Software project. Like me and my team will estimate the various requirements of cost, time, and resources throughout in our project. As we look upon the activity duration estimation looks at the time it takes to complete the entire project, activity duration estimation is dependent on other time and resource estimates also. We might start on these estimates at the Starting of our project, but we make the most of the estimates during the planning period. Estimates are never exact these are just guesses by the whole team. But we can improve our accuracy by dividing the estimation task into three distinct steps: determining a Work Breakdown Structure (WBS), estimating the amount of work and duration of work packages, and calculating the project schedule. Technique’s Which Are Used to Estimate Project Duration We can choose from many other methods, however, if neither CPM nor PERT meets our needs. Other estimating methods include:  Bottom-up  Expert judgment  Function point  Historical comparison  Top-down  Objects point
4. 4. Page 4 of 16 Out of all these methods I will discuss CPM and Pert in detail rest I will discuss briefly. So I am discussing each of them one by one… Top Down Approach As we all know that the effort for a project is a function of many parameters. And the main factor which determine the effort for the project is basically the size of the project. That is if we have larger project the greater is the effort requirement and greater is the project duration. So top down approach basically takes effort as a function of project size and it is important to note down that to apply this function we first have to determine the size of the project for which effort has to be estimated and project duration is to be estimated. If the past productivity for similar projects is known than we can use them to determine the effort and time duration from the size. A more general function for determining effort from size that is commonly used is of the form: EFFORT = a * SIZEb , where a and b are constants, and project size is generally in KLOC (size could also be in another size measure called function points which can be determined from requirements). Values for these constants for an organization are determined through regression analysis, which is applied to data about the projects that have been performed in the past. For example, Harsh and Vinod analyzed the data of more than 60 projects done at LPU InfoTech Division, ranging from 4000 to 467,000 lines of delivered source code, and found that if the SIZE estimate is in thousands of delivered lines of code (KLOC), the total effort, E, in person-months (PM) can be given by the equation E = 5.2(SIZE).91. It should be noted that to use the top-down approach for estimation, even if we have a suitable function, we need to have an estimate of the project size. In other words, we have replaced the problem of effort estimation by size estimation because size estimation is often easier than direct effort
5. 5. Page 5 of 16 estimation. This is mainly due to the fact that the system size can be estimated from the sizes of its components by adding the size estimates of all the components. Similar property does not hold for effort estimation, as effort for developing a system is not the sum of effort for developing the components as additional effort is needed for integration and other such activities when building a system from developed components. Clearly for top-down estimation to work well, it is important that good estimates for the size of the software be obtained. There is no known simple method for estimating the size and duration accurately. When estimating software size, the best way may be to get as much detail as possible about the software to be developed and to be aware of our biases when estimating the size of the various components. By obtaining details and using them for size estimation, the estimates are likely to be closer to the actual size and duration for the final software. Bottom up Approach This approach works in this way that the people who are going to do work in the project work will participate in estimation process. The team is basically the project team members and project manager who will develop estimating data the lowest level in the work breakdown structure Bottom-up estimating is where the people who were going to do the work participate in the estimating process. When the estimates of work, duration and cost are set at that level they are aggregated upward into estimates of higher level deliverables and the project as a whole. Bottom-up estimating is the most accurate approach to estimating cost and duration and also usually requires the most time. This kind of estimating involves the entire project team and gives people the opportunity to participate in the development of the estimates used to measure their work. As a result, bottom-up estimating tends to develop a much higher level of project team commitment than does top-down or parametric estimating. In top-down, where the numbers come from an
6. 6. Page 6 of 16 outside source, people feel we have imposed the estimates on them. The drawback of the bottom-up approach is that it consumes much more time than the other estimating techniques. In bottom-up estimating, we follow a three-step process, working from the lowest level of detail in the work breakdown structure. We begin bottom-up estimating by developing a detailed work package to accompany the WBS. In this work package, we may describe risk elements, dependencies that affect the activity and its cost and duration. Once the work package is complete and the team member is comfortable with it, we can proceed to develop the actual cost or duration estimate. In bottom-up estimating, a project manager has to be careful not to force an estimate on the project team member. If the estimate is forced, the project manager cannot expect to earn much commitment from the team member. That commitment is dependent on a free and open negotiation where the team member feels the estimate is fair and reasonable. At this point in the process, the project manager may use the three estimates from the PERT process, as that allows an estimate that reflects the uncertainty inherent in the task. Last, we aggregate the estimates for each of the activities in the lowest level of the WBS and roll the numbers up to develop estimates for the major deliverables and the project as a whole. We can use a number of mathematical techniques with bottom-up estimating although the most popular and most accurate is to use three point estimates where the team members provide the pessimistic, optimistic and best guess numbers for the three-point calculations. Expert Judgments This is basically asking someone who is knowledgeable about the application area or the development environment to give an estimate of the effort needed to carry out a task. This method will be used when estimating the effort and time needed to change the existing piece of the software or developing the similar kind of software, the estimator would
7. 7. Page 7 of 16 have to carry the analysis in order to judge the proportion of code that would be affected that derive an estimation from the person who is familiar to be in the best position to do this. But the true fact is that is simple guessing. Historical comparison This basically based on the cased based reasoning. The estimator seeks out the projects that have been completed and that have similar characteristics to the new project. The effort and time that has been recorded for the matching source case can be used as base estimate for the target. The estimator should try to identify any differences between the target and source and make the adjustments to the base estimate for new project duration and effort. Functional Points Alan Albrecht while working for IBM, recognized the problem in size measurement in the 1970s, and developed a technique (which he called Function Point Analysis), which appeared to be a solution to the size measurement problem The principle of Albrecht’s function point analysis (FPA) is that a system is decomposed into functional units. Inputs : information entering the system Outputs : information leaving the system Enquiries : requests for instant access to information Internal logical files : information held within the system
8. 8. Page 8 of 16 External interface files: information held by other system that is used by the system being analyzed. So on the basis of this we basically estimate the time duration for different kind of functional points etc. Object points The approach was devised at the Leonard N. stern school of business, New York University. It has similarities with FP approach, but takes different account of features. The approach uses counts of screen, reports and 3gl component that an application might possess it is these that referred to as objects. Each object has to be classified as one of the following… 1. Simple 2. Medium 3. Difficult The number of objects at each level are multiplied by the approiate complexity weighting as shown in the figure.
9. 9. Page 9 of 16 CPM (Critical path method) In this we basically capture the activities and their inter-relationships using a graph Lines are used to represent the activities. Nodes are used to represent the start and stop of activities. With the help of cpm we can calculate the two things The forward pass in which we calculate the earliest state of the activities and calculate the project completion date.
10. 10. Page 10 of 16 The backward pass in which we calculate the latest start for activities and identify the critical path from the graph. Some common terms in this Critical event : an event that has zero slack Critical path : a path joining those critical events. Example to construct a CPM
11. 11. Page 11 of 16
12. 12. Page 12 of 16 Pert PERT is a planning and control tool used for defining and controlling the tasks necessary to complete a project. PERT charts and Critical Path Method (CPM) charts are often used interchangeably; the only difference is how task times are computed. Both charts display the total project with all scheduled tasks shown in sequence. The displayed tasks show which ones are in parallel, those tasks that can be performed at the same time. A graphic representation called a "Project Network" or "CPM Diagram" is used to portray graphically the interrelationships of the elements of a project and to show the order in which the activities must be performed. PERT planning involves the following steps:
13. 13. Page 13 of 16 1. Identify the specific activities and milestones. The activities are the tasks of the project. The milestones are the events that mark the beginning and the end of one or more activities. 2. Determine the proper sequence of activities. This step may be combined with #1 above since the activity sequence is evident for some tasks. Other tasks may require some analysis to determine the exact order in which they should be performed. 3. Construct a network diagram. Using the activity sequence information, a network diagram can be drawn showing the sequence of the successive and parallel activities. Arrowed lines represent the activities and circles or "bubbles" represent milestones. 4. Estimate the time required for each activity. Weeks are a commonly used unit of time for activity completion, but any consistent unit of time can be used. A distinguishing feature of PERT is it's ability to deal with uncertainty in activity completion times. For each activity, the model usually includes three time estimates: o Optimistic time - the shortest time in which the activity can be completed. o Most likely time - the completion time having the highest probability. o Pessimistic time - the longest time that an activity may take. From this, the expected time for each activity can be calculated using the following weighted average: Expected Time = (Optimistic + 4 x Most Likely + Pessimistic) / 6 This helps to bias time estimates away from the unrealistically short timescales normally assumed. 5. Determine the critical path. The critical path is determined by adding the times for the activities in each sequence and determining the longest path in the project. The critical path determines the total calendar time required for the project. The
14. 14. Page 14 of 16 amount of time that a non-critical path activity can be delayed without delaying the project is referred to as slack time. If the critical path is not immediately obvious, it may be helpful to determine the following four times for each activity: o ES - Earliest Start time o EF - Earliest Finish time o LS - Latest Start time o LF - Latest Finish time These times are calculated using the expected time for the relevant activities. The earliest start and finish times of each activity are determined by working forward through the network and determining the earliest time at which an activity can start and finish considering its predecessor activities. The latest start and finish times are the latest times that an activity can start and finish without delaying the project. LS and LF are found by working backward through the network. The difference in the latest and earliest finish of each activity is that activity's slack. The critical path then is the path through the network in which none of the activities have slack. The variance in the project completion time can be calculated by summing the variances in the completion times of the activities in the critical path. Given this variance, one can calculate the probability that the project will be completed by a certain date assuming a normal probability distribution for the critical path. The normal distribution assumption holds if the number of activities in the path is large enough for the central limit theorem to be applied. 6. Update the PERT chart as the project progresses. As the project unfolds, the estimated times can be replaced with actual times. In cases where there are delays, additional resources may be needed to stay on schedule and the PERT chart may be modified to reflect the new situation. An example of a PERT chart is provided below:
15. 15. Page 15 of 16 Benefits to using a PERT chart or the Critical Path Method include:  Improved planning and scheduling of activities.  Improved forecasting of resource requirements.  Identification of repetitive planning patterns which can be followed in other projects, thus simplifying the planning process.  Ability to see and thus reschedule activities to reflect interproject dependencies and resource limitations following know priority rules.  It also provides the following: expected project completion time, probability of completion before a specified date, the critical path activities that impact completion time, the activities that have slack time and that can lend resources to critical path activities, and activity start and end dates. Conclusion This helps us to estimate the project duration estimation which later helps to create a comprehensive estimate which will reflect the different tasks and real-world scheduling. This approach will removes the uncertainty and creates a project plan that helps us to know our options and adapt to path changes. The duration estimation also help us to estimate the budget of our project. As we all know that estimates can never be exact but practicing this will make our guesses better.
16. 16. Page 16 of 16 Bibliography https://4pm.com/bottom-up-estimating/ https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0CEkQ FjAE&url=http%3A%2F%2Frpl-blog.blogspot.com%2F2010%2F03%2F411-top-down-estimation- approach.html&ei=ajtCU6HCKoKOrQfpuYCQDw&usg=AFQjCNE1N13_-t8ZjUaaW- 01OkYFzanMaQ&sig2=svgx9iA9JqHABaLf2HeKvw&bvm=bv.64367178,d.bmk https://slideshare.com