Spotfire Statistica® Quality Control Charts

During the earlier stages of developing a production process, Spotfire Statistica® Design of Experiments is often used to optimize two quality characteristics.

1. deviations from target specifications
2. excessive variability around target specifications

The Quality Control module is used to monitor on-going production processes for quality characteristics. Flexible implementations of Pareto charts, X-bar charts, R charts, S charts, S-squared (variance) charts, C charts, Np charts (binomial counts), P charts (binomial proportions), U charts, CuSum (cumulative sum) charts, moving range charts, runs charts (for individual observations), regression control charts, MA charts (moving average), and EWMA charts (exponentially-weighted moving average) are provided. These charts may be based on user-specified values or on parameters (e.g., means, ranges, proportions, etc.) computed from the data. 

Most of the variable control charts can be constructed from single observations (e.g., moving range chart) as well as from samples of multiple observations. Control limits can be specified in terms of multiples of sigma (e.g., 3 * sigma), in terms of normal or non-normal (Johnson-curves) probabilities (e.g., p=.01, .99), or as constant values. For unequal sample sizes, control charts can be computed with variable control limits or based on standardized values. For most charts, multiple sets of specifications can be used in the same chart (e.g., control limits for all new samples can be computed based on a subset of previous samples, etc.). Runs tests, such as the Western Electric Run Rules, are easily integrated into the QC chart. 

Analytics and visualizations are available for use with the "Define, Measure, Analyze, Improve, Control" (DMAIC) methodology.

Note: For detailed descriptions of quality control charts and extensive annotated examples, see Buffa (1972), Duncan (1974) Grant and Leavenworth (1980), Juran (1962), Juran and Gryna (1970), Montgomery (1996), Shirland (1993), or Vaughn (1974). Two excellent introductory texts with a "how-to" approach are Hart & Hart (1989) and Pyzdek (1989). There are also two German-language texts on this subject; Rinne and Mittag (1995) and Mittag (1993).