Inspections, Sampling, & other tools

December 9, 2009

We discuss here the balance of the two of Ishikawa’s seven tools of quality and a few more of tools and techniques used in QC processes. Statistical sampling, inspection and review of approved change requests are the other tools & techniques used in QC processes and are discussed here.

Run charts are similar to control charts. The difference is that in does not show any of the limits displayed in control charts. For example the upper and lower limits as well as upper and lower control limits are not indicated. Thus it is a plot of measurements related to output items as the process runs. Thus this plot is able to clearly show variations over time, if drifts are happening or there is a declining drift, process improvements/declines over time etc. Thus this curve is easily amenable to trend analysis and let you mathematically predict future outcomes. Trend analysis will show up technical performance such as how many defects have been identified and how many have been corrected and how many remain etc. Time and cost trends also can be obtained that show how many activities show significant variances.

A scatter diagram is used to plot two variables against each other. The resulting graph can clearly indicate if the two variables are correlated. If they are not, one would expect the points generated from the values of the two variables to be random. The graph formed will then be a completely scattered set of points against the two axes. Whereas if they have strong correlation the graph would resemble a diagonal line, indicate that the value of one variable influences directly the other. This information then can be further used in determining root causes or planning a design of experiment.

Statistical sampling is all about taking samples, conducting measurements on them and drawing conclusions about the complete population from these data. The size of samples and how frequently they are to be taken are guided by statistical theories. Thus the QC personnel will need to be conversant with the theoretical background of such sampling and be able to decide the right size of the samples to be taken from the population of items we want to subject to QC activities. Sample are selected and tested as defined in the quality plans.

Inspections are about checking work products and determining if these conform to standards drawn up for the project. These may be from organizations own quality standards or specifically drawn up for the project. Inspections are carried out throughout the life of the project. How frequently or at what project steps are defined in the quality plan. The inspection level can be at any level and has to be determined a priori. The inspection level could be at a specific attribute level or right up to a set of measurements related to a product. Inspections are used to confirm defect repairs too. Peer review, Walkthroughs, audits etc are other synonyms that may be used in literature or in an organization.

Review of approved change requests is another tool that can help implement QC processes. Changes required are identified during QC activities. These are approved by the QC and the project teams. But to be doubly sure these should be subjected to review to determine if any of the requests are not really needed or an opportunity to improve a process has been missed.

Armed with these tools the QC department carries out the planned QC activities for a project.

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