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.

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 chart A candlestick chart (also called Japanese candlestick chart or K-line) is a style of financial chart used to describe price movements of a security, derivative, or currency. It is similar to a bar chart in that each candlestick represents all f ...

s or

open-high-low-close chart An open-high-low-close chart (also OHLC) 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 (the highest and lowest prices) over one ...

s. As originally conceived, the multi-vari chart resembles a

Shewhart individuals control chart In statistical quality control, the individual/moving-range chart is a type of control chart used to monitor variables data from a business or industrial process for which it is impractical to use rational subgroups. The chart is necessary in t ...

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

specifications A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type of technical standard. There are different types of technical or engineering specificati ...

rather than

control limits Process Window Index (PWI) is a statistical measure that quantifies the robustness of a manufacturing process, e.g. one which involves heating and cooling, known as a thermal process. In manufacturing industry, PWI values are used to calibrate t ...

. The three panels are interpreted as follows:

Recent usage

More recently, the term "multi-vari chart" has been used to describe a visual way to display

analysis of variance Analysis of variance (ANOVA) is a collection of statistical models and their associated estimation procedures (such as the "variation" among and between groups) used to analyze the differences among means. ANOVA was developed by the statistician ...

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 chart Control charts is a graph used in production control to determine whether quality and manufacturing processes are being controlled under stable conditions. (ISO 7870-1) The hourly status is arranged on the graph, and the occurrence of abnormalit ...

s, the vertical axis depicts the quality characteristic of interest (or experimental response)

References

{{DEFAULTSORT:Multi-Vari Chart Quality control tools Statistical charts and diagrams