Which of the following charts have upper control limits, but frequently have lower control limits of zero?

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Question restatement: The prompt asks which charts have upper control limits (UCL) but frequently have lower control limits (LCL) of zero.
Option 1: c and u charts. These charts focus on defect counts per item or per unit, with LCL typically at or near zero in many practical applications, and they do have an upper control limit in some cases. However, the characteristic described—a frequently zero LCL—is more strongly associated with range-based and variability charts rather than defect-count charts. This option is partially plausible but not the strongest or clearest match for the given phrasing.
Option 2: p and np charts. These are proportion-based charts where UCLs exist and LCLs can be zero if the observed proportion is very small or zero. In practice, many p-chart calculations do yield a zero LCL under certain conditions, so this option could fit the criterion. Nevertheless, the wording of the question emphasizes charts where the LCL is frequently zero due to the fundamental non-negativity of the statistic, which is a more defining feature for range and dispersion charts.
Option 3: x-bar and individuals charts. The x-bar chart has both an upper and lower control limit around the process mean, and the individuals chart (I-chart) also has limits; however, their LCLs are not inherently zero and can be positioned below the process mean depending on data and subgrouping. Therefore, this pair does not align with the described frequent LCL of zero.
Option 4: R and sigma charts. Here, the R chart controls dispersion by the range, which cannot be negative, making its LCL effectively zero in many setups. The sigma (or s) chart tracks standard deviation, which also cannot be negative, leading to a natural LCL of zero in standard practice. Both charts inherently feature an upper control limit and a lower limit that is zero or effectively zero, matching the described characteristic very clearly.
In summary, while several options involve charts with LCLs that can be zero under certain conditions, the combination of R and sigma charts most consistently embodies the explicit combination of having an upper control limit while frequently having a lower control limit of zero, due to the nonnegative nature of range and standard deviation. The other options either do not consistently exhibit a zero LCL, or their typical LCL behavior does not align as cleanly with the description.

ISE 4120 SP2025 (10663) QCI Chapter 9 Quiz

Which of the following charts have upper control limits, but frequently have lower control limits of zero?

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