Which of the following conditions must be met before a process capability study can be...

The correct answer is D. The process must be in control . The CSSBB source states that process capability can be defined as the normal behavior of a process when operating in a state of statistical control . It further explains that the only tool that helps determine stability is the control chart , and that capability calculations such as Cp and Cpk fairly show future performance when the process is consistent over time, meaning in statistical control .

This is a core Six Sigma principle: a capability study assumes the process behavior is stable and predictable. If the process is out of control, the variation is not consistent, so any capability number may be misleading. While many traditional capability calculations do use continuous data, the key prerequisite in this question is process stability. The target value and process documentation may be useful, but they are not the essential statistical condition required before a valid capability study is performed. Therefore, the verified CSSBB answer is D. The process must be in control .