Question

What is the difference between statistical process control and randomized control trial?  How are the two approaches similar?

Answer 1

Statistical process control

Statistical Process Control, SPC is method of measuring and controlling quality by monitoring the manufacturing process. SPC is an effective method to drive continuous improvement. Quality data in the form of Product or Process measurements are obtained in real-time during manufacturing. This data is then plotted on a graph with pre-determined control limits. Control limits are determined by the capability of the process.

An advantage of SPC over other control methods is that production is less affected. There is less interruption and process slowdowns than with more direct examination and inspection methods.

Disadvantages of SPC are, it takes time to apply rigorously in a manufacturing setting, as it requires more observations. Also Implementation of SPC is a costly endeavor.

Randomized control trial:

A study design that randomly assigns participants into an experimental group or a control group. As the study is conducted, the only expected difference between the control and experimental groups in a randomized controlled trial (RCT) is the outcome variable being studied.

Advantages of randomized control trial

• Good randomization will “wash out” any population bias
• Easier to blind/mask than observational studies
• Results can be analyzed with well known statistical tools
• Populations of participating individuals are clearly identified

Disadvantages of randomized control trial

• Expensive in terms of time and money
• Volunteer biases: the population that participates may not be representative of the whole
• Does not reveal causation
• Loss to follow-up attributed to treatment