# Statistical process control with x-chart | Free template

Statistical process control with x-chart is a free template to control and ensure that the processes are producing in accordance with established standards. Statistical process control is a statistical method used to measure the performance of a process.

A process is in statistical control when the only source of variation comes from natural causes, that is, when the only variation is random. Statistical process control is important for quality because it is important to know when changes have occurred in a process so as to identify and address the root causes of the changes before a large number of defective units come out of the process. Statistical process control uses the concept of hypothesis testing, when the zero-hypothesis is rejected, the process is out of control.

An x-chart for statistical process control is a chart showing points of mean values for each sample being compared against a central line and an upper and a lower control limit. Sample selection is made at different times and for each sample mean and standard deviation is calculated. A process is out of control when a sample mean exceeds the upper control limit or when a sample mean are below the lower control limit. The central line is calculated as the average of all the sample means, the upper control limit (UCL) is calculated as the mean plus the mean of all the sample standard deviations times the z-value and the lower control limit (LCL) is calculated as the mean minus the mean of all the sample standard deviations times the z-value.

You can use this template to establish a statistical process control for sample means so as to check whether a process in statistical control or out of statistical control. If a process is out of control you have to investigate and address the root causes of the problems in the process.

**Updated: **01/01/2015 | Created by All-templates.biz

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quality variation process probability