What is Statistical process control?
{{complex|date=June 2014}} '''Statistical process control (SPC)''' is the use of [[statistics]] to access the [[stability]] of a process and the [[quality]] of what that process creates. Proper use of SPC can result in faster and better production. SPC is very valuable to companies as a way to make producing their product less expensive and keep their customers happy. A good example of SPC being used is a [[Bottle|bottling plant]], a type of factory where bottles are filled with liquid. The system that creates filled bottles is called a ''process''. The [[weight]] of the [[liquid]] added to a bottle is very important for the bottling plant's [[cost control]] and [[Customer service|customer]] satisfaction. If the target is to fill each bottle with 250 grams of liquid, it is still acceptable if some bottles are filled with another amount between 245 and 255 grams. SPC could be used to make sure that the process is being done well and that the weight of each bottle is in that range. SPC relies on [[Quantity|quantitative]] and graphic analysis of measurements to evaluate observed variation. If the attributes of interest (filled bottle weight in this example) vary within an acceptable range, a process is said to be ''in control,'' ''in statistical control,'' or ''stable.'' When unacceptable variation is noted (i.e., filled bottle weight is discovered to be below 245 grams or above 255 grams), actions are typically taken to determine and correct their cause. In the bottling plant example, suppose, too many bottles are filled with less than 245 grams. Checking the plant equipment reveals that one of ten filler valves is failing to work. SPC was first used in the 1920s. It is used in manufacturing and in many other kinds of repeated activities. Much of the power of SPC lies in the ability to examine a process using tools which give weight to [[objective]] analysis over [[subjective]] opinions and which allow the strength of each source to be determined numerically. Variations in the process, which might affect the q