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Objective Defect Evaluation Leads Improvement Efforts

Many times it is imperative for a firm to improve the quality of its deliverables even though it is operating consistently at a high sigma level. Such continuous improvement is also necessary when addressing various levels of the capability maturity model integration (CMMI), a software process guide. CMMI Level 5 calls for a proactive reduction in variation and a shift in the mean, while Level 3 involves addressing continuous improvement from a reactive position. The difficulty in completing these tasks, however, is knowing where to start. When no process area is clearly failing, but the drive for continuous improvement remains, such as in the completion of CMMI Level 5, practitioners should use an end-effect rating system to determine where to focus efforts.

Considering Errors

Selecting a direction for improvement can be hard if no one step in a software process is producing significant errors. Consider this example from a service firm that delivers computer aided drafting (CAD) models and drawings, and needs to reduce defects in drawings. Figure 1 shows the generic flow of the activities.

Figure 1: Flow Chart of CAD Models and Drawings Delivery Process

Figure 1: Flow Chart of CAD Models and Drawings Delivery Process

In order to improve the process, the data has to be logged and analyzed. Once the data is captured (Table 1), it can be organized in a Pareto chart for analysis (Figure 2).

Table 1: Errors in CAD Drawings
Category of ErrorsNumber of Errors
Dimensions1
Typographical error in notes1
Part number1
Base object model (BOM)1
Views not matching1
Digital raster graphic (DRG) format1
Part naming1
Angle of projection1
Datum reference1
Missed out feature1
Sketch constraints1
Geometric dimensioning and tolerances (GD&T)1
Assembly mismatch1
Figure 2: Error Categories in Pareto Analysis

Figure 2: Error Categories in Pareto Analysis

But it would be inappropriate to use the data in this Pareto to take corrective action; it is a random plot of the data because each category had the same number of errors: one. Other methods must be used to determine the best course of action.

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Finding Direction

In order to objectively analyze and take corrective action in instances where a solution is not readily available, a simplified version of the FMEA (failure mode and effects analysis) can be used. The FMEA caters to the Design phase of the product life cycle management. CMMI and Six Sigma practitioners use a similar approach to imagine failure during the Design phase and address it by way of either incorporating redundancy or redesign. The following is a simplified version of the FMEA concept. It incorporates a severity number, failure effect number and end effect number, which are assigned to each error category.

Arriving at the End Effect Number

Severity is rated on a scale of 1 to 4, with 4 being the most severe potential consequences of failure. The classifications for each rating are listed in Table 2.

Table 2: Severity Number Classifications
Severity CategoryFailure EffectSeverity Number
Catastrophic-Loss of life, life threatening or resulting in permanent injury or occupational illness
-Loss of launch site facilities
-Loss of system
-Long-term detrimental environmental effects
4
Critical-Temporarily disabling or occupational illness, but not life threatening
-Loss or major damage to systems or facilities
-Loss or major damage to public or private property
-Short-term detrimental effects
3
Major-Mission or system degradation2
Negligible-Any other effect1

The failure effect number is determined using the same four-option scale as the severity number, but is based on the immediate consequences of the failure. The end effect number is the product of the severity number and the failure effect number.

The severity, failure effect and end effect numbers for the CAD example are shown in Table 3.

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Table 3: End Effect Number Calculation
Category of ErrorsSeverity NumberFailure Effect NumberEnd Effect Number
Dimensions4416
Typographical error in notes111
Part number111
BOM224
Views not matching111
DRG format111
Part naming111
Angle of projection122
Datum reference3412
Missed out feature4416
Sketch constraints111
GD&T3412
Assembly mismatch224

Data may also be sorted and displayed (Figure 3) with regard to the end effect number.

Figure 3: End Effect Numbers for Error Categories

Figure 3: End Effect Numbers for Error Categories

This rating system gives practitioners a more objective understanding and direction as to how to go about further analyzing the data and taking corrective action. This can give rise to a Six Sigma DMAIC project, and also justifies continuous improvement toward achieving CMMI Level 5.

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