Current Defects
The significance of this sector is in that the only dependence between model years, advanced and current, is captured in "Fraction of Current Tasks Defective", the probability of doing a current task incorrectly. This fraction is a function of the number of advanced tasks completed when the product was in its advanced phase. It also is used to determine the fraction of defective current tasks, thus the fraction of those that fail testing in the Current Work Sector, and those that are the source of defects at launch in the Market Defects Sector.
(027) Change in Frac Tasks Comp in Previous Phase=IF THEN ELSE(Months to Introduction Date=12,Fraction of Advanced Task Completed this Model Year/TIME STEP,0)
Units: 1/Month
The Fraction of Advanced Tasks Completed at the end of the model year is kept in a memory stock.
(088) Fraction of Tasks Completed in Previous Phase= INTEG (+Change in Frac Tasks Comp in Previous Phase-Decr in Frac Tasks Comp in Prev Phase,1)
Units: dimensionless
This is the memory stock of the Fraction of Tasks Completed in Previous Phase.
(063) Decr in Frac Tasks Comp in Prev Phase= IF THEN ELSE(Months to Introduction Date=12,Fraction of Tasks Completed in Previous Phase/TIME STEP,0)
Units: 1/Month
The memory stock of the Fraction of Tasks Completed in Previous Phase is emptied at the end of the model year and then transferred into the next memory stock.
(075) Frac Comp in Prior Previous Phase= INTEG (+Decr in Frac Tasks Comp in Prev Phase-Decr in Frac Comp in Prior Prev Phase,1)
Units: dimensionless
This is the memory stock of the Fraction of Advanced Tasks Completed in Prior Previous Phase.
(059) Decr in Frac Comp in Prior Prev Phase= IF THEN ELSE(Months to Introduction Date=12,Frac Comp in Prior Previous Phase/TIME STEP,0)
Units: 1/Month
The memory stock of the Fraction of Tasks Completed in Prior Previous Phase is reset at the end of the model year.
The model developed so far is based on the assumption that the defect fraction is divided into two fixed components, the fraction of defects that cannot be eliminated by advanced tasks, the Unavoidable Defects, and the fraction that can, the Avoidable Defects. The introduction of additional up-front development tools is modeled by making these two parameters variable and assuming that they are determined by the size of the set of tools currently in use. The contribution by the fraction of the Avoidable Defects is determined by the Fraction of Tasks Completed in the Previous Phase. The more tasks completed in the Advanced Work Sector, the less the defect fraction.
(086) Fraction of Curr Tasks Defective= Frac of Avoidable Defects*(1-Fraction of Tasks Completed in Previous Phase)+Frac of UnAvoidable Defects
Units: dimensionless
The Fraction of Current Tasks Defective is the sum of the UnAvoidable Defects and the Avoidable Defects. The contribution by the "Fraction of the Avoidable Defects" is determined by the Fraction of Tasks Completed in the Previous Phase. The more tasks completed the less the defect fraction.
(140) Total Defect Frac= 0.75
Units: dimensionless
This is the Total Defect Fraction.
(082) Frac of UnAvoidable Defects=(1-Historical Comp Frac of Advanced Tasks)*Total Defect Frac
Units: dimensionless
The Maximum Fraction of Avoidable Defects is a "fraction" of the Total Defect Fraction. This "fraction" is the Historical Completion Fraction of Advanced Tasks, determined by the size of the set of tools currently in use. Thus, if there were many advanced tasks completed historically, then the Maximum Fraction of UnAvoidable Defects is lower.
(080) Frac of Avoidable Defects=Total Defect Frac*Historical Comp Frac of Advanced Tasks
Units: dimensionless
The Maximum Fraction of Avoidable Defects is the defects that can be eliminated by doing the advanced work. It is a "fraction" of the Total Defect Fraction. This "fraction" is the Historical Completion Fraction of Advanced Tasks, determined by the size of the set of tools currently in use. Thus, if there were many advanced tasks completed historically, then the Maximum Fraction of Avoidable Defects is higher.
The benefit of the new tools is captured by changes in the split between unavoidable and avoidable defects. While the sum of the avoidable and unavoidable defects is constant at the Total Defect Fraction, the split is determined by the "Historical Completion Fraction of Advanced Tasks".
(094) Historical Comp Frac of Advanced Tasks= Adv Task Comp Last Yr 2/Total Number of Possible Adv Tasks
Units: dimensionless
The Historical Completion Fraction of Advanced Tasks is calculated by the Average Advanced Tasks Completed divided by the Total Number of Possible Advanced Tasks. This represents the efficacy of the tool set currently in use. This captures the organization's current ability to use the tools it has at its disposal. It is calculated as a moving average of the organization's current knowledge of the tools. Once a tool is learned, time is required to develop experience before it can be used effectively. The average time required to gain such experience is assumed to be two model years.
The "Historical Completion Fraction of Advanced Tasks" is a moving average of the "organization's current knowledge of the tools" which captures that fact that, once a tool is learned, time is required to develop experience before it can be used effectively. This represents the efficacy of the tool set currently in use and it is the organization's current ability to use the tools it has at its disposal. The average time required to gain such experience is assumed to be two model years.
(119) Learning Delay in Years= 1e+009
Units: months
This represents the delays for Learning and gaining Experience in the new tool set. The variable's actual units are in years but due to technical reasons the units here are set to months. So, "Learning Delay in Years = 1" means that Learning Delay is 1 year.
(120) Learning Delay Per Stage= Learning Delay in Years/2
Units: months
This represents the delays for Learning and gaining Experience in the new tool set.
(100) Inc in Adv Comp Last Yr 2= IF THEN ELSE(Months to Introduction Date=12,Adv Task Comp Last Yr 2*((Learning Delay Per Stage-1)/Learning Delay Per Stage)/TIME STEP +Adv Task Comp Last Yr 1*(1/Learning Delay Per Stage)/TIME STEP,0)
Units: tasks/Month
This is the inflow to the delay representing Experience with the new tool set.
(010) Adv Task Comp Last Yr 2= INTEG (Inc in Adv Comp Last Yr 2-Incr In Adv Com Two Yrs prior 2,New Advanced Tasks Per Yr)
Units: tasks
This stock represents the recent fraction of advanced tasks completed using the methodology. The delay represents the time required to gain experience with the new tools.
(104) Incr In Adv Com Two Yrs prior 2= IF THEN ELSE(Months to Introduction Date=12,Adv Task Comp Last Yr 2/TIME STEP,0)
Units: tasks/Month
This is the outflow to the delay representing Experience with the new tool set.
The "organization's current knowledge of the tools" captures the delays inherent in learning how to use new tools. Here, the average learning delay is assumed to be 1 model year. Thus, if the feasible set of tools is increased, the organization does not immediately benefit from using them. Instead time is required to learn the new tools and develop the appropriate skill.
(098) Inc in Adv Comp Last Yr 1= IF THEN ELSE(Months to Introduction Date=12,Adv Task Comp Last Yr 1*((Learning Delay Per Stage-1)/Learning Delay Per Stage)/TIME STEP+ Advanced Completed Flushed*(1/Learning Delay Per Stage),0)
Units: tasks/Month
This is the inflow to the delay representing Learning of the new tool set.
(008) Adv Task Comp Last Yr 1= INTEG (Inc in Adv Comp Last Yr 1-Incr In Adv Com Two Yrs prior 1,New Advanced Tasks Per Yr)
Units: tasks
This stock represents the recent fraction of advanced tasks completed using the methodology. The delay represents the time required to learn how to use the new tools.
(102) Incr In Adv Com Two Yrs prior 1= IF THEN ELSE(Months to Introduction Date=12,Adv Task Comp Last Yr 1/TIME STEP,0)
Units: tasks/Month
This is the outflow to the delay representing Learning of the new tool set.
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