20th InternationalSystem Dynamics Conference, 2002

Paper Title “Dynamics of Schedule Pressure on

Software Projects”Presentation by V.K.Rai

SD-2002, RAI, V.K.

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Abstract This paper studies the dynamics of schedule pressure in software projects. It

constructs a system dynamics model of the software development process, which includes the following modules. Flow of Work, Work Being Done, Inspection, Fault Detection and Rework, and Supplementary Variables. It includes the module ‘Effect of Schedule Pressure’ and integrates it with the rest of the model. The model presents the results of two sets of schedule-related policies of a system dynamics model. The first set of policies that pertain to the base model does not consider the effect of schedule pressure on the staff productivity and errorproneness while the second set of policies pertaining to the revised model does. This study finds that effect of schedule pressure on software project is non-linear and dynamics of schedule pressure is intricately related to decision making process of the project manager, thus, making software projects management complex and counterintuitive.

Key words: Schedule pressure, software projects, productivity, errorproneness, and decision making

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Figure1: A Simplified View of the Effects of Schedule Pressure

++

– +

Schedule pressure

Errorproneness

Work rate

Productivity

+ +

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Figure 2: Work Being Done

Work to be done Work Really Done

WBDCWTDR WUF

WBDF WNR

TWCW

MARUW

NS

PNS

TWCN

FFWCNFWCN ES

PES

PCFES

PCFNS

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Abbreviations for Figure 2 WTDR: Work To be Done due to Rework WBDC: Work Being Done Correctly WBDF: Work Being Done with Fault WUF: Work with Undetected Fault MARUW: Maximum Allowable Rate of Undertaking Work WNR: Work Needing Rework TWCW: Total Work Completed per Week TWCN: Total Work Completed Normally FWCN: Faulty Work Completed

Normally FFWCN: Fault Free Work Completed Normally ES: Experienced Staff NS:

New Staff PES: Productivity of Experienced Staff PNS: Productivity of New Staff PCFES: Propensity of Fault Commitment for Experienced Staff PCFNS:Propensity of Fault Commitment for New Staff

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Figure 3: Inspection, Fault Detection and Rework

Work to be done Work Really Done

WBDCWTDR WUF

WBDF WNR

AWNR

TWNR

RMW

TRSPCT

SPCTITMW

TIW

TIWN

WIN

FFD

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Abbreviations for Figure 3

WTDR: Work To be Done due to Rework WBDC: Work Being Done Correctly WBDF: Work Being Done with Fault WUF: Work with Undetected

Fault WNR: Work Needing Rework WIN: Work being Inspected AWNR: Average Work Needing Rework TWNR: Time to smooth WNR FFD: Fraction of Faults Detected RMW: Rework Multiplier

from Work ITMW: Inspection Time Multiplier from Work TIW: Time to Inspect Work

SPCT: Schedule Project Completion Time TIWN: Time to Inspect Work Normal

TRSPCT: Time Relative to Schedule Project Completion Time

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Effect of Schedule Pressure on Productivity and Errorproneness of Staff

Table -1:

Productivity andErrorproneness

LowSchedule

Pressure (2)

MediumSchedule

Pressure (3)

HighSchedule

Pressure (4)For Exp.

Staff (PES)High3.0

Medium toLow3.0

Medium toLow2.5

Productivity(Tasks perweek perperson) For New

Staff (PNS)High2.0

Medium toLow2.0

Medium toLow1.5

For Exp.Staff

(PCFES)

Low0.15 or 15%

Medium0.2 or 20%

Medium0.2 or 20%

Errorproneness

(Dimensionless) For New

Staff(PCFNS)

Low0.25 or 25%

Medium0.4 or 40%

Medium0.4 or 40%

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Figure 4: Two Control Feedback Loops of the Effect of Schedule Pressure

Sector 1

R

Work_to_be_done

Time_Required

Time_Ratio

Schd_Pressure

Productivity

WBDC

Loop 2 (Effect of Schedule Pressure)

R

Work_to_be_done

Time_Required

Time_Ratio

Schd_Pressure

Errorproneness

WBDC

Loop 1 (Effect of Schedule Pressure )

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Policy runs Two sets of schedule related policies considered first set pertains to the base model it does not consider effect of schedule pressure second set pertains to the revised model it considers effect of schedule pressure schedule estimations considered are:SPCT= 40 weeks (optimistic estimation)SPCT= 50 weeks (normal estimation)SPCT = 60 weeks (pessimistic estimation)Fact = two experienced and two new development staff Assumption= no body leaves and joins the project in the middle

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Figure 5: Base Model Policy Runs with Constant Productivity and ErrorpronenessPerformance Variables of Base Model (SPCT = 50 weeks)

2:43 AM 5/19/01

0.00 25.00 50.00 75.00 100.00

Time

1:

1:

1:

2:

2:

2:

3:

3:

3:

4:

4:

4:

0.00

50.00

100.00

1: PWRD 2: PWPD 3: EOR 4: EOL

1

1

1

1

2

2

2

2

3

3

3 3

4 44

4

Performance (SPCT = 50 weeks)

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Figure 6: Comparison of Work to be done for the Base Model Policies

12:33 AM 5/19/01

0.00 25.00 50.00 75.00 100.00

Time

1:

1:

1:

0.00

200.00

400.00

1: Work to be done 2: Work to be done 3: Work to be done

1

1

1

1

2

2

2

2

3

3

3

3

work done (different SPCT)

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Schedule Policy Runs at Project Completion Time (PCT) Table 2: Some important results of the base model

WC: Total Work Content of the Project; WUF: Work with Undetected Faults, WI : Initial Work Content of the Project: 400 Tasks.

Schedule

Policy

PCT

(weeks)

PWRD

(%)

PWPD

(%)

WC

(tasks)

EOR

(%)

WUF

(tasks)

EOL

(%)

SPCT=40 68.00 97.48 99.86 498 24.41 12.25 3.06

SPCT=50 74.00 97.51 99.87 543 35.74 12.80 3.20

SPCT=60 81.00 97.80 99.88 591 47.80 12.28 3.07

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Revised Model Policy Runs with Varying Values of Productivity and Errorproneness

Effect of schedule pressure on productivity and Errorproneness considered

Schedule related policies remain the same as in base model

figure 7 shows the rise of schedule pressure for the revised model, SPCT = 50 weeks

Figure 8 performance variables PWRD, PWPD, EOR & EOL for the revised model, SPCT = 50 weeks

Figure 9 compares the three policies with respect to Work to be done (W)

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Figure 7: Changes in Schedule Pressure with the Time Ratio

2:17 AM 5/19/01

0.00 25.00 50.00 75.00 100.00

Time

1:

1:

1:

2:

2:

2:

0.00

0.50

1.00

1.00

2.00

3.00

1: TR 2: SP

1

1

1 12

2

2 2

Graph 1 (Schedule Pressure)

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Figure 8: Performance Variables of Revised Model (SPCT = 50 weeks)

2:40 AM 5/19/01

0.00 25.00 50.00 75.00 100.00

Time

1:

1:

1:

2:

2:

2:

3:

3:

3:

4:

4:

4:

0.00

50.00

100.00

1: PWRD 2: PWPD 3: EOR 4: EOL

1

1

1

1

2

2

2

2

3

33 3

4 44

4

Performance (SPCT = 50 weeks)

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2:43 AM 5/19/01

0.00 25.00 50.00 75.00 100.00

Time

1:

1:

1:

0.00

200.00

400.00

1: Work to be done 2: Work to be done 3: Work to be done

1

1

1

1

2

2

2

2

3

3

3

3

work done (different SPCT)

Figure9: Comparison of work to be done for the revised model policies

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Some of the important results of the revised model. Table 3

Schedule

Policy

PCT

(weeks)

PWRD

(%)

PWPD

(%)

WC

(tasks)

EOR

(%)

WUF

(tasks)

EOL

(%)

SPCT=40 74.00 97.82 99.89 489 22.29 10.09 2.52

SPCT=50 72.00 97.91 99.89 511 27.70 10.10 2.53

SPCT=60 73.00 98.05 99.89 544 35.98 10.01 2.50

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Conclusion Effect of schedule pressure on productivity and

errorproneness is non-linear The base model shows significant increase in (PCT)

with increase in SPCT Revised model shows little increase in PCT with

increase in SPCT Extent of rework increases from 22% to 36% as SPCT

increases from 40 weeks to 60 weeks Extent of latent error, another measure of software

quality, remains around 2.5% for all cases

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