What type of control chart should be used to study the above data? Answer: An I-MR chart should be used dues to measurement data and a subgroup size of one.

Question

Options

• AAn I-MR chart should be used dues to measurement data and a subgroup size of one.

• A
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Explanation

Option A is correct because an I-MR (Individuals and Moving Range) chart is specifically designed for continuous measurement data collected one observation at a time - a subgroup size of 1. The "I" chart tracks individual data points over time, while the "MR" chart tracks the moving range between consecutive points as a proxy for process variation, since you can't calculate within-subgroup variation with only one observation.

Note: Only one choice (A) is listed, so there are no distractors to evaluate here. If this question had distractors, common wrong answers would typically be:

• X-bar & R / X-bar & S charts - wrong because these require subgroup sizes ≥ 2 (usually n = 5+), where you can compute within-subgroup averages and ranges.
• p or np charts - wrong because those are for attribute data (counts of defectives), not continuous measurement data.
• c or u charts - wrong because those count defects per unit, not measurements.

Memory tip: Think "I = Individual = 1." If your subgroup size is 1 and your data is measured (not counted), reach for the I-MR chart. The "MR" compensates for not having a within-subgroup range by comparing each point to its neighbor.

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