Multi-vari chart
Encyclopedia
In quality control
, multi-vari charts are a visual way of presenting variability through a series of charts. The content and format of the charts has evolved over time.
s or open-high-low-close chart
s.
As originally conceived, the multi-vari chart resembles a Shewhart individuals control chart with the following differences:
The three panels are interpreted as follows:
data (typically be expressed in tabular format). It consists of a series of panels which portray minimum, mean, and maximum responses for each treatment combination of interest rather than for periods of time.
Because it is a two-dimensional representation of multiple dimensions (one for each factor in the ANOVA), the multi-vari chart is only useful for comparing the variability among at most four factors.
The chart consists of the following:
Quality control
Quality control, or QC for short, is a process by which entities review the quality of all factors involved in production. This approach places an emphasis on three aspects:...
, multi-vari charts are a visual way of presenting variability through a series of charts. The content and format of the charts has evolved over time.
Original concept
Multi-vari charts were first described by Leonard Seder in 1950, though they were developed independently by multiple sources. They were inspired by the stock market candlestick chartCandlestick chart
A candlestick chart is a style of bar-chart used primarily to describe price movements of a security, derivative, or currency over time.It is a combination of a line-chart and a bar-chart, in that each bar represents the range of price movement over a given time interval. It is most often used in...
s or open-high-low-close chart
Open-high-low-close chart
An open-high-low-close chart is a type of chart typically used to illustrate movements in the price of a financial instrument over time. Each vertical line on the chart shows the price range over one unit of time, e.g. one day or one hour...
s.
As originally conceived, the multi-vari chart resembles a Shewhart individuals control chart with the following differences:
- The quality characteristic of interest is measured at two extremes (around its diameter, along its length, or across its surface) and these measurements are plotted as vertical lines connecting the minimum and maximum values over time.
- The quality characteristic of interest is plotted across three horizontal panels that represent:
- Variability on a single piece
- Piece-to-piece variability
- Time-to-time variability
- The quality characteristic of interest is plotted against upper and lower specificationsSpecification (technical standard)A specification is an explicit set of requirements to be satisfied by a material, product, or service. Should a material, product or service fail to meet one or more of the applicable specifications, it may be referred to as being out of specification;the abbreviation OOS may also be used...
rather than control limitsControl limitsControl limits, also known as natural process limits, are horizontal lines drawn on a statistical process control chart, usually at a distance of ±3 standard deviations of the plotted statistic from the statistic's mean....
.
The three panels are interpreted as follows:
| Panel | Condition | Corrective action |
|---|---|---|
| Variability on a single piece | Lengths of the vertical lines (i.e., the range Range (statistics) In the descriptive statistics, the range is the length of the smallest interval which contains all the data. It is calculated by subtracting the smallest observation from the greatest and provides an indication of statistical dispersion.It is measured in the same units as the data... ) exceed one-half the specifications (or more) |
Repair or realignment of tool |
| Piece-to-piece variability | Excessive scatter | Examine process inputs for excessive variability—lengths of the vertical lines are estimates of process capability Process capability A process is a unique combination of tools, materials, methods, and people engaged in producing a measurable output; for example a manufacturing line for machine parts... |
| Time-to-time variability | Appearance of a non-stationary process Stationary process In the mathematical sciences, a stationary process is a stochastic process whose joint probability distribution does not change when shifted in time or space... |
Examine process inputs or steps for evidence of shifts or drifts |
Recent usage
More recently, the term "multi-vari chart" has been used to describe a visual way to display analysis of varianceAnalysis of variance
In statistics, analysis of variance is a collection of statistical models, and their associated procedures, in which the observed variance in a particular variable is partitioned into components attributable to different sources of variation...
data (typically be expressed in tabular format). It consists of a series of panels which portray minimum, mean, and maximum responses for each treatment combination of interest rather than for periods of time.
Because it is a two-dimensional representation of multiple dimensions (one for each factor in the ANOVA), the multi-vari chart is only useful for comparing the variability among at most four factors.
The chart consists of the following:
- One horizontal panel for each level of the outermost factor
- One cluster of points representing the minimum, mean, and maximum responses for the particular treatment combination, connected by lines for each level of the innermost factor
- In the case of four factors, vertical panels for each level of the next-innermost factor
- As with control chartControl chartControl charts, also known as Shewhart charts or process-behaviour charts, in statistical process control are tools used to determine whether or not a manufacturing or business process is in a state of statistical control.- Overview :...
s, the vertical axis depicts the quality characteristic of interest (or experimental response)