Which plot will give the earliest indication of a shift or trend?

• A. Levy-Jennings
• B. Tonks-Youden
• C. Cusum
• D. Histogram

Answer: (C)

A method that detects small, gradual shifts by accumulating information over time will reveal a trend earlier than one that looks at individual points. The cumulative sum (Cusum) chart does exactly this: it builds the running sum of deviations from a target value, so a persistent drift makes the cumulative sum rise or fall steadily and cross a signaling threshold sooner than a single outlier would on a traditional control chart. This heightened sensitivity to small, sustained changes is why Cusum is the best choice for early indication of a shift or trend.

Levy-Jennings plots rely on individual points relative to a target and control limits, so they tend to detect larger shifts when a point breaches a limit or runs beyond certain rules, but they’re less responsive to small, continuous drifts. A histogram summarizes data from a single time window and shows distribution shape rather than any temporal trend, so it’s not suited for early trend detection. Tonks-Youden plots (a type of method comparison plot) focus on relationships between two measurements rather than time-ordered shifts, so they aren’t designed for early trend detection in a process.