Problem Diagnosis
&
Introduction to
Project Dynamics
1.040/1.401J
Nathaniel Osgood
4/13/2004
Topics
„
Problem Diagnosis
Pareto Analysis
„ Fishbone Diagram
„ Scatterplots
„
„
Systems Thinking and System Dynamics
Causal Loop Diagrams
„ System Dynamics
„
Insights into Causes of Problems
„
„
„
„
„
Discussed Last Time : Exploratory Analysis
Pareto Analysis
Fishbone Diagram
Scatter Diagram
Causal Loop Diagram
Pareto Analysis
„
„
„
•
•
Correctly addressing a small portion of project
components can provide control over the remaining
project components.
Help identify the contributors to given types of
performance, mostly cost and quality performance.
Group A: a small portion of the major cost components that
account for a significant portion of the total cost
Group B: all cost component other than Group A and C
components
Group C: a large portion of the minor cost components that
account for a trivial portion of the total cost
Pareto Analysis
„
Example: Drivers of
Quality Problems in
Building
Construction
Workers
Rebar workers
Concrete
workers
Carpenters
Mortar
workers
Frequency
10
15
20
5
Topics
„
Problem Diagnosis
Pareto Analysis
„ Fishbone Diagram
„ Scatterplots
9
„
Systems Thinking and System Dynamics
Causal Loop Diagrams
„ System Dynamics
„
Fishbone (“Cause and Effect”)
Diagram
„
„
„
Help identify the drivers of given
performance problems, by providing a
format with which managers can easily
understand cause and effect relationships.
The causes for a given performance
problem are analyzed by initially defining
the problem and then channelling possible
causal relations on the defined problem
into predetermined (proj.-specfic)categories
Subcauses shown as progressively refined
branches
Fishbone Diagram
„
Example: Delay in concrete
pouring
Controllable Causes
Workers
Equipment
Lack of Experience
Hiring Temporary
Workers
Use of Inefficient
Concrete Pump
Low Productivity
Late Arrival of
Concrete Pump on the 1st Day
Schedule Delay
Rains in the Morning of the
3rd Day
Uncontrollable Causes
LEGEND
Effects
Categories
2nd Cause
3rd Cause
1st Cause
Topics
„
Problem Diagnosis
Pareto Analysis
9 Fishbone Diagram
„ Scatterplots
9
„
Systems Thinking and System Dynamics
Causal Loop Diagrams
„ System Dynamics
„
Scatter Diagram
„
„
„
Help predict the trend of future performance
by showing the correlation between different
variables.
The data set used in a scatter diagram
consists of an independent variable and a
dependent variable
Representing the independent variable on
the horizontal axis and the dependent
variable on the vertical axis, a scatter diagram
can plot the correlation between two
variables
Scatter Diagram
„
Different types of
correlations
Scatter Diagram Disadvantages
„
„
Correlation does not necessitate a causal linkage
Many potential directions of causal chains could
explain a given correlation
E.g. suppose A is correlated with B
„ Possible Causal linkages
„
A
B
B
A
A
B
B
A
C
Topics
9
Problem Diagnosis
Pareto Analysis
9 Fishbone Diagram
9 Scatterplots
9
„
Systems Thinking and System Dynamics
Causal Loop Diagrams
„ System Dynamics
„
Systems Thinking and
System Dynamics
„
Systems thinking focuses on
Conceptualizing problems in broader context
„ Emphasizes interconnections rather than
reductionist reasoning
„ Internal rather than internal factors
„ Feedback structure of system as primary determinant
of behavior
„
„
Common manifestations
Qualitative: Causal loop diagrams
„ Quantitative: System dynamics
„
Systems Thinking and
Project Management
„
Primary critique: Traditional methods too
Fragmented
„ Restrictive in assumptions
„ Local in attention to implications of changes
„ Hesitant regarding representation of “soft” factors
„ Too dependent on people link components
„ Too willing to ignore important “side effects”
„
„
Seen as potentially major contributor in project
Learning (model captures institutional knowledge)
„ Planning (identify robust decision rules, leverage pts)
„ Control (how to best handle deviations)
„
„
Critique of Fragmentation
Consider traditional discrete methods
CPM, Resource algs, time/cost tradeoffs, productivity
considerations, manual check of global
„ Activities analyzed in isolation (local impact of delaying
activity or extending activity duration)
„
„
Productivities, resource use, quality, cost all linked
„
Delay/extension of activity influences resources,
morale, productivity, etc.
„ Takes people from other activities, idles others
„ May affect customer relations, allocation of labor to project
(⇒ lower quality)
„ Requires reconsidering subcontractor, material procurement
„ Makes overtime, concurrency more likely
„
„
Typical schedulers do not think through all implications
Plans is always changing, being updated
Causal Loop Diagram
„
Like fishbone diagram, focus on causation
„
„
Contrast with correlation focus of scatterplot
More general, expressive than fishbone
Cyclic: Focus on capturing feedback effects
„ Indicate sign of causal impact (+ vs. –)
indicates
„ x →+y
∂y
>0
indicates ∂x
„ x→y
„
∂y
<0
∂x
Causal Loop Diagram
„ An
arrow with a positive sign (+): “all else
remaining equal, an increase (decrease) in
the first variable increases (decreases) the
second variable above (below) what it
would otherwise have been.”
„ An arrow with a negative sign (-): “all else
remaining equal, an increase (decrease) in
the first variable decreases (increases) the
second variable below (above) what it
otherwise would have been.”
Reasoning about Link Polarity
„
„
Easy to get confused regarding link polarity in
the context of a causal chain
Tips for reasoning about link polarity for X→Y
Reason about this link in isolation – do not be
concerned about links preceding X or following Y
„ Ask “if X were to INCREASE, would Y increase or
decrease”?
„
„ Increase in Y implies “+”, Decrease in Y implies “-”
„ If answer is not clear or depends on value of X, need to
think about representing several paths between X and Y
Ambiguous Link
„
Ambiguous Link: Sometimes +, sometimes Overtime
„
Productivity
Replace this by disaggregating causal pathways by
showing multiple links
Fatigue
+
-
Overtime
Productivity
+
+
Longer Hours
Feedback Loops
„
Loops in a causal loop diagram indicate feedback
in the system being represented
„
„
Qualitatively speaking, this indicates that a given
change kicks off a set of changes that cascade
through other factors so as to either amplify
(“reinforce”) or damp (“balance”) original change
Loop classification: product of signs in loop
Balancing loop: Product of signs negative
„ Reinforcing loop: Product of signs positive
„
Simple Causal Loops
Worker
Productivity
Remaining Work
+
-
Change Requests
+
Perceived
Completion Date
Perceived Slack
+
-
+
Project Duration
Target
Completion Date
Job Rhythm
-
+
Changes to
Schedule
Aggregate
Productivity
-
-
Willingness of Project
Participants to share info
with PM
Overbearing PM
Management Style
-
+
PM Suspicion
Estimated Design Costs
beyond Target Budget
Target Budget
Design Scope
+
-
Elaborating Causal Loops 1
+
Estimated Design Costs
beyond Target Budget
Target Budget
Design Scope
+
Target Budget
-
Estimated Design Costs
beyond Target Budget
Design Scope
+
Elaborating Causal Loops 2
Work Pressure
+
+
Work Remaining
-
Productivity
Work Pressure
+
+
Fatigue
+
Work Remaining
-
Productivity
Evolving More Complex Diagrams
Relationship with
Owner
Relationship with
Owner
Labor Productivity
-
-
Delay
-
+
-
+
Morale
Disputes with
Owner
+
Disputes with
Owner
Schedule Pressure +
+
Relationship with
Owner
Labor Productivity
+
-
Delay
Delay
-
Morale
-
-
Delay
+
-
-
+
-
Labor Productivity
Concern About
Cost of Delay
Relationship with
Owner
-
Disputes with
Owner
Morale
+
-
Disputes with
Owner
Causal loop example
T argeting early
project completion
-
P roject scope
completeness
+
Design
change
Design and construction
requests from owner
overlapping
+
-
Schedule p ressure
+
Delay
+
+
Design
+ completeness
Design change requests
from construction
workers
+
+
Construction+
change
Design change
Deadline and Milestone Control
+
Overtime
Increasing
+ resources
+
Schedule
slippage
Schedule delays
+
+
Time to completion
-
Aggressive
scheduling
Work remaining
+
-
+
Work rate
+
Productivity
+
Schedule pressure
+
Cutting the
corner
+
Defects
Causal Loop Structure :
Dynamic Implications
„
„
Each loop in a causal loop diagram is
associated with qualitative dynamic behavior
Most Common Single-Loop Modes of
Dynamic Behavior
Exponential growth
„ Goal Seeking Adjustment
„ Oscillation
„
„
When composed, get mixture of behaviors
„
e.g. Growth and Plateau
CL Dynamics: Exponential Growth
(First Order Reinforcing Loop)
„
Example
+
Word of
Mouth Sales
+
+
Customers
Graph for Stock
„
Dynamic implications
20,000
15,000
10,000
5,000
0
0
10
Stock : Current
20
30
40
50
60
Time (Month)
70
80
90
100
CL Dynamics: Goal Seeking
(Balancing Loop)
„
„
Example:
Dynamic behavior
Potential
- Customers
Word of +
Mouth Sales
75
50
25
0
0
10
20
Inventory : Current
30
40
50
60
Time (Month)
70
80
90
100
CL Dynamics: Oscillation
(Balancing Loop with Delay)
„
Causal Structure
+
Desires Inventory
Inventory
- Finishing
+
Producing Production
+
Starts
demand vs. production
„
Dynamic Behavior:
6,857
3,142
0
30
Time (year)
demand : Oscil
producing : Oscil
tons/year
tons/year
Growth and Plateau
„
Loop structure:
Potential
- Customers
-
Reinforcing Loop
„ Balancing Loop
„
Word of
+ Mouth Sales
+
+
„
Dynamic Behavior:
Customers
+
Graph for Customer
100,000
75,000
50,000
25,000
0
0
10
Customer : Current
20
30
40
50
60
Time (Month)
70
80
90
100
Design/Construction Overlap
Uncertainties
Assumptions in
Design
Owner's Requests
on Changes
Overlapping between
Design and Construction
Oversizing
Project
Costs
Project
Duration
Potential Design
Change Impact on
Construction
Construction Processes
Design Changes
Overlapping
Construction Work
R2 Done before Upstream
Completed
Increase in
Time Pressure
Workforce
Estimated Project
Duration
R1
Delay
Productivity R3
Construction
Changes
Construction Phasing Overlap
Uncertainties
Assumptions in
Design
Owner's Requests
on Changes
Overlapping between
Design and Construction
Oversizing
Project
Costs
Potential Design
Change Impact on
Construction
Construction Processes
Overlapping
R2
Project
Duration
Time Pressure
Design Changes
Construction Work
Done before Upstream
Completed
Increase in
Workforce
R1
Estimated Project
Duration
Productivity
Delay
R3
Construction
Changes
Topics
9
Problem Diagnosis
Pareto Analysis
9 Fishbone Diagram
9 Scatterplots
9
„
Systems Thinking and System Dynamics
Causal Loop Diagrams
„ System Dynamics
9
System Dynamics
„
Many frameworks for project systems analysis
Discrete event sim., Agent-based sim.
„ System dynamics is most popular
„
„
Greatest competitive advantage in systems that are
Nonlinear
„ Feedback rich
„ Exhibit delays
„ Less governed by low-level heterogeneity
„
System Dynamics Basics
„
Represents system as coupled series of ordinary
differential equations (ODEs)
Standard state-equation formulation
„ Continuous time formulation
„ Stochastic components permissible (special handling)
„ Analytic solutions not possible: Numerically integrate
„
„
Graphical representation for problem focus
State equations as stocks
„ Components of differentials as follows
„ Intermediate computations as auxiliaries, table functions,
etc.
„
How a SD Model is Created
„
„
Conceptualize system using causal loop diagram
Convert CLD to “stock & flow” structure
State variables (accumulations) as stocks
„ Changes to state variables as flows
„
„ All change
in system state occurs through flows
All loops include at least one stock
„ Intermediate calculations, outputs as auxiliaries
„
„
„
„
Add to equations to capture relations among vars
Calibrate to historic data
Run scenarios to identify effect, robust policies
Example Creation of a
System Dynamics Model
„
Step 1: Map out Causal Loops
Potential
- Customers
Word of
+ Mouth Sales
+
Customers
„
Step 2: Identify state variables of interest
Potential
Customers
„
+
Customers
Step 3: Identify flows of interest
Potential
Customers
Customers New Customers
+
Example Creation of a System
Dynamics Model
„
Step 4: Define Supporting Variables
Fraction of Customers
in Population
Total Population
Likelihood of Potential
Customer Joining
Function Giving Likelihood of
Potential Customer Becoming New
Customer based on Fraction of
Customers
Potential
Customers
Customers New Customers
„
Insert equations to describe linkages
„
E.g.
„
„
Total Population = Customers+Potential Customers
Fraction of Customers in Population= Customers/Total Population
Example Creation of a
System Dynamics Model II
„
Step 1: Map out Causal Loops
Work Pressure
Work Remaining
Productivity
Step 2: Identify state variables of interest
Work
Remaining
Fatigue
„
Step 3: Identify flows of interest
Work
Remaining
Work Being
Completed
Fatigue
Growth in Fatigue due
to Schedule Pressure
Fatigue
+
-
„
+
+
Recovery from
Fatigue
Example Creation of a System
Dynamics Model
Initial Work Size
Work Hours as a Function
of Fraction of Work
Fraction of Work
Completed
Completed
Normal
Productivity
Work
Remaining
Work Hours
Normal Work
Hours
Work Being
Completed
Productivity Coefficient as a
Function of Direct Work
Pressure
Fatigue
Growth in Fatigue due
to Schedule Pressure
Recovery from
Fatigue
Mean time to Recover
From Fatigue
Productivity Coefficient
from Fatigue
Productivity coeefficient
from Fatigue as a Function
of Fatigue