Section 8.3 Perform Quality Control

Performing quality control (QC) involves monitoring specific project results to determine whether they comply with relevant quality standards and identifying ways to eliminate causes of unsatisfactory results. It should be performed throughout the project. Quality standards include project processes and product goals. Project results include deliverables and project management results, such as cost and schedule performance. QC is often performed by a quality control department or similarly titled organizational unit. QC can include taking action to eliminate causes of unsatisfactory project performance.

The project management team should have a working knowledge of statistical quality control, especially sampling and probability, to help evaluate QC outputs. Among other subjects, the team may find it useful to know the differences between the following pairs of terms:

Tolerances (the result is acceptable if it falls within the range specified by the tolerance) and control limits (the process is in control if the result falls within the control limits).

Attribute sampling (the result conforms, or it does not) and variables sampling (the result is rated on a continuous scale that measures the degree of conformity).

Prevention (keeping errors out of the process) and inspection (keeping errors out of the hands of the customer).

Approved change requests ( Section 4.4.1.4 ) can include modifications such as revised work methods and revised schedule. The timely correct implementation of approved changes needs to be verified.

Work performance information ( Section 4.4.3.7 ), including technical performance measures, project deliverables completion status, and the implementation of required corrective actions, are important inputs to QC. Information from the project management plan about the planned or expected results should be available along with information about the actual results and implemented change requests.

Section 8.3.2 Perform Quality Control: Tools and Techniques

The first seven of these are known as the Seven Basic Tools of Quality.

.1 Cause and Effect Diagram

Cause and effect diagrams, also called Ishikawa diagrams or fishbone diagrams, illustrate how various factors might be linked to potential problems or effects. Figure 8-6 is an example of a cause and effect diagram.

8-6. :

Cause and Effect Diagram

.2 Control Charts

A control chart’s purpose is to determine whether or not a process is stable or has predictable performance. Control charts may serve as a data gathering tool to show when a process is subject to special cause variation, which creates an out-of-control condition. Control charts also illustrate how a process behaves over time. They are a graphic display of the interaction of process variables on a process to answer the question: Are the process variables within acceptable limits? Examination of the non-random pattern of data points on a control chart may reveal wildly fluctuating values, sudden process jumps or shifts, or a gradual trend in increased variation. By monitoring the output of a process over time, a control chart can be employed to assess whether the application of process changes resulted in the desired improvements. When a process is within acceptable limits, the process need not be adjusted. When a process is outside acceptable limits, the process should be adjusted. The upper control limit and lower control limit are usually set at +/- 3 sigma (i.e., standard deviation).

Control charts can be used for both project and product life cycle processes. An example of project use of control charts is determining whether cost variances or schedule variances are outside of acceptable limits (for example, +/- 10 percent). An example of product use of control charts is evaluating whether the number of defects found during testing are acceptable or unacceptable in relation to the organization’s standards for quality.

Control charts can be used to monitor any type of output variable. Although used most frequently to track repetitive activities, such as manufactured lots, control charts also can be used to monitor cost and schedule variances, volume and frequency of scope changes, errors in project documents, or other management results to help determine if the project management process is in control. Figure 8-7 is an example of a control chart of project schedule performance.

8-7. :

Example of a Control Chart of Project Schedule Performance

.3 Flowcharting

Flowcharting helps to analyze how problems occur. A flowchart is a graphical representation of a process. There are many styles, but all process flowcharts show activities, decision points, and the order of processing. Flowcharts show how various elements of a system interrelate. Figure 8-8 is an example of a process flowchart for design reviews. Flowcharting can help the project team anticipate what and where quality problems might occur and, thus, can help develop approaches for dealing with them.

8-8. :

Sample Process Flowchart

.4 Histogram

A histogram is a bar chart showing a distribution of variables. Each column represents an attribute or characteristic of a problem/situation. The height of each column represents the relative frequency of the characteristic. This tool helps identify the cause of problems in a process by the shape and width of the distribution.

8-9. :

Pareto Diagram (Chart

.5 Pareto Chart

A Pareto chart is a specific type of histogram, ordered by frequency of occurrence, which shows how many defects were generated by type or category of identified cause (Figure 8-9). The Pareto technique is used primarily to identify and evaluate nonconformities.

In Pareto diagrams, rank ordering is used to guide corrective action. The project team should take action to fix the problems that are causing the greatest number of defects first. Pareto diagrams are conceptually related to Pareto’s Law, which holds that a relatively small number of causes will typically produce a large majority of the problems or defects. This is commonly referred to as the 80/20 principle, where 80 percent of the problems are due to 20 percent of the causes. Pareto diagrams also can be used to summarize all types of data for 80/20 analyses.

.6 Run Chart

A run chart shows the history and pattern of variation. A run chart is a line graph that shows data points plotted in the order in which they occur. Run charts show trends in a process over time, variation over time, or declines or improvements in a process over time. Trend analysis is performed using run charts. Trend analysis involves using mathematical techniques to forecast future outcomes based on historical results. Trend analysis is often used to monitor:

• Technical performance. How many errors or defects have been identified, how many remain uncorrected?

• Cost and schedule performance. How many activities per period were completed with significant variances?

.7 Scatter Diagram

A scatter diagram shows the pattern of relationship between two variables. This tool allows the quality team to study and identify the possible relationship between changes observed in two variables. Dependent variables versus independent variables are plotted. The closer the points are to a diagonal line, the more closely they are related.

.8 Statistical Sampling

Statistical sampling involves choosing part of a population of interest for inspection (for example, selecting ten engineering drawings at random from a list of seventy- five). Appropriate sampling can often reduce the cost of quality control. There is a substantial body of knowledge on statistical sampling; in some application areas, it may be necessary for the project management team to be familiar with a variety of sampling techniques.

.9 Inspection

An inspection is the examination of a work product to determine whether it conforms to standards. Generally, the results of an inspection include measurements. Inspections can be conducted at any level. For example, the results of a single activity can be inspected, or the final product of the project can be inspected. Inspections are also called reviews, peer reviews, audits, and walkthroughs. In some application areas, these terms have narrow and specific meanings. Inspections are also used to validate defect repairs.

.10 Defect Repair Review

Defect repair review is an action taken by the quality control department or similarly titled organization to ensure that product defects are repaired and brought into compliance with requirements or specifications.