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Project Estimation: Metrics and Measurement

Persons and Months Calculated Efforts (in pm) of task/project = Number of persons X duration in months The efforts for a task with 2 persons working for 3 months is 3 x 2 = 6 pm A worker can be full time or part-time Full-Time Equivalent (FTE) number of workers = Sum (number of part-time x percent) + Number of full time workers For example: A project with 4 workers at 75%, 3 others at 50%, and 2 full-time. The FTE is: (4X.75)+(3x.5)+2 =6.5 persons

The mythical person-month

Metrics Guidelines Use common sense and organizational sensitivity when interpreting metrics data. Provide regular feedback to the individuals and teams who have worked to collect measures and metrics. Work with practitioners and teams to set clear goals and metrics that will be used to achieve them. Don’t use metrics to appraise individuals and never use metrics to threaten individuals or teams. Metrics data that indicate a problem area should not be considered “negative.” These data are merely an indicator for process improvement. Don’t obsess on a single metric to the exclusion of other important metrics.

Types of Metrics Size oriented metrics: Based on number of lines of code (LOC) to be written. Function oriented metric: Based on number of Function Points (FP) to be completed.

Typical Size-Oriented Metrics
errors per KLOC (thousand lines of code) defects per KLOC \$ per LOC page of documentation per KLOC errors / person-month LOC per person-month \$ / page of documentation

Typical Function-Oriented Metrics
errors per FP (thousand lines of code) defects per FP \$ per FP pages of documentation per FP FP per person-month

Why FP Measures?

Computing Function Points
F P = Count-total x Complexity (Count-total =  count x weight, Complexity = ([ x  Fi])

Taking Complexity into Account
Formula: F P = count-total x [ x  Fi]

Exercise Compute the Function Point (FP) value ( F P = count-total x [ x  Fi]): Count Weighting Factor Number of user inputs Number of user outputs Number of inquiries Number of files Number of external interface The complexity adjustments values rating (Fi) are: Critical value of performance: 3 Heavy operational environment: 3 On line: 3 Multiple screen operation: 3 On-line master files update: 3 Complexity of I/O: 3 Complexity of internal processing: 4 Backup and recovery: 4 Data communications: 4 Distributed Processing: 4 Reusable code: 4 Conversion: 4 Multiple installations: 4 Facilitation of changes: 4

Function Point Value Exercise
Total-count= (10x4+20x5+15x4+3x10+5x8)=270  Fi = )= 50 Function Points = 270 x ( x50) =310.5 FPs

Cost Estimation

Conventional Methods Total Efforts = Estimated efforts required per FP x Size in FPs Or: Total efforts = Estimated efforts required per KLOC x Size in KLOCs KLOC : Thousand Lines of Code

Empirical Estimation Models

Example: LOC Approach

Project Staffing Estimation
The unit of measure for project HR efforts is person-months (pm). For a project with two persons who work for one month the total efforts is 2 persons * 1 month = 2 pm. Efforts in pm= number of full time workers * duration in months Number of full-time workers = Efforts/ Duration

Empirical Estimation Models
General model: E = A + B (ev)c where: A, B, C: empirically derived constant ev: estimated variable of size in terms of KLOC or FP Samples models: E= 5.2 (KLOC) .091 (Walston-Felix) E= (KLOC) 1.16 (Bailey-Basili) E=3.2 (KLOC) (Doty) E= FP (Albrech and Gaffney) E= FP (Matson, Barnett, and Mellichamp)

COCOMO

COCOMO: Basic Model

Example: COCOMO

COCOMO II Total Efforts in pm = 3.13 x (KLOC)1.072 Example: for a software module of 8050 LOCs Total efforts= 3.13 X(8.05) = pm For a cost of \$10,000/pm Total cost = \$29,280

Estimation Guidelines

Metric for Software Quality
Correctness Maintainability Integrity = Sum [1 - threat x (1- security)] Usability Number of defects found and removed Defect Removal Efficiency = Total defects that exist at stage

Exercise 1 Efforts of a 3 person project is originally estimated at 12 person-months. However, after two months only 40% completed. 1. Compute the remaining efforts in person-months. Let T = total revised efforts Efforts consumed : 3 p x 2 m = 6 pm 6 pm = .40 x T T= 15 pm 2. If you wanted to hire more workers to meet the completion schedule, how many should you hire? Remaining efforts = 15 – 6 = 9 pm for 2 months Number of new hires = (9/2) – 3 = 1.5 (2 rounded) 3. If each new worker only works at 70% capacity and requires training that reduces the productivity of an experienced worker 20%, can the project meet the deadline in the remaining 2 months? FTE = 2 x x x .70 = 4 Full Time workers 4 x 2 = 8 pm Required efforts 9 pm, 1 pm short.

Exercise #2 Use the Basic COCOMO model to estimate efforts and duration of an embedded software development project with size of 55 KLOC. 1. How many workers should be hired for this project? Embedded: a=3.6 b=1.2, c= 2.5, d = .32 2. If the project must be completed within 15 months, how many additional workers should be hired?

Solutions Embedded: a=3.6 b=1.2, c= 2.5, d = .32
1. How many workers should be hired for this project? Embedded: a=3.6 b=1.2, c= 2.5, d = .32 Efforts= 3.6*(55)1.2 = pm Duration = 2.5 * (441.3).32 = months Number of workers needed: /17.54 = 25.1 2. If the project must be completed within 15 months, how many additional workers should be hired? Number of workers required for 15 month completion: 441/15=29.4 Additional workers: 29.4 – 25.1 = 4.3 rounded to 5

Group Project Meeting

Homework 3: Due Sunday 3/15 @11:59 PM D2L Dropbox
Efforts of a 5 person project is originally estimated at 40 person-months. However, after 3 months only 30% completed. Compute the remaining efforts in person- months. If you wanted to hire more workers to meet the completion schedule, how many should you hire? If each new worker only works at 70% capacity and requires training that reduces the productivity of an experienced worker 20%, can the project meet the deadline in the remaining 3 months?

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