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Evaluating web site activity is tricky business. Because web activity varies constantly, the challenge is to separate everyday random variation from the non-random changes due to marketing programs, web site design, or search engine rank.

Failure to recognise the sources of variation correctly can result in one of two errors:

1) Random variation in activity is ‘explained’ by a change in marketing or the web site when no “real” change in activity occurred.

2) A real change in activity is actually ignored.

Either of the two above errors wastes resources and business opportunities.

Enter Statistical Process Control. SPC charts were specifically invented to separate the two sources of variation. While control charts have been most commonly used in manufacturing processes, they ‘work’ with virtually any time series. Additionally, they are easy to understand and use. On a control chart, upper and lower control limits are automatically calculated to separate common variation from special variation. Points inside the control limits are due to common variation. Points outside the limits are due to special causes. To make the charts even more sensitive to small, sustained shifts in level, ‘pattern rules’ are also used. An example rule is, “Eight consecutive points above the centre line signals a special cause.”

If a shift in level is identified, a separate set of control limits can be applied to pre- and post-shift data.

As an example, web site traffic can be analysed by charting the weekly number of web sessions on a company web site. Every week, the count of sessions where three or more pages were hit is charted. Our SPC software product, NWA Quality Analyst, automatically extracts the data from a SQL Server database of web logs and charts the data. All the user has to do is enter the desired date range.

Such charts can help attribute variation in website traffic to the correct cause. SPC can help to…

1) Measure the effect of marketing campaigns and web adverts on web traffic

2) Illustrate the effect on web traffic of changes in web site navigation

3) Identify the most popular online articles

NorthWest Analytical Statistical Process Control software is supplied and supported in the UK and Ireland by Adept Scientific plc, Amor Way, Letchworth, Herts. SG6 1ZA; telephone (01462) 480055, fax (01462) 480213, email quality@adeptscience.co.uk; or see Adept’s World Wide Web site http://www.adeptscience.co.uk/. Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

With offices in the UK, USA, Germany and throughout the Nordic region, Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.