What does cusum indicate when control data are randomly scattered about the expected mean?

What does cusum indicate when control data are randomly scattered about the expected mean?

• A. Cusum, in control
• B. Cusum, systematic error
• C. Westgard Rules
• D. 10x Westgard Rules

Answer: (A)

CUSUM monitors the cumulative departure of each observation from the target mean, so it’s especially good at detecting small, gradual shifts. When control data are randomly scattered around the expected mean, there’s no consistent bias or drift; positive and negative deviations cancel out over time, keeping the cumulative sum near zero and within limits. That pattern signals the process is in control. Westgard rules, by contrast, apply to Shewhart charts and look for larger, rule-based out-of-control patterns, not the random scatter scenario described.

CUSUM monitors the cumulative departure of each observation from the target mean, so it’s especially good at detecting small, gradual shifts. When control data are randomly scattered around the expected mean, there’s no consistent bias or drift; positive and negative deviations cancel out over time, keeping the cumulative sum near zero and within limits. That pattern signals the process is in control. Westgard rules, by contrast, apply to Shewhart charts and look for larger, rule-based out-of-control patterns, not the random scatter scenario described.