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WORKSHOP PROCEEDINGS
Tourism & creative industry . Valencia, July, 11&12th, 2013
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satisfaction. When subgroup standard deviations are used instead, the control
chart properties are improved, but implementation is much more complicated
because subgroup sizes are large and vary due to different response rates.
Two alternative charts that are more appropriate for survey data are discussed.
The first is an extension of the p chart to the case where there are more than
two possible outcomes. The second chart is based on the chi-squared statistic,
which is commonly used to test hypotheses when data are categorical. The
use of each chart is illustrated, and their properties are compared using the
hospital data. The comparison shows that the chi-squared chart detects shifts
faster on average than does the extension of the p-chart. The chi-squared chart
is somewhat difficult to compute and interpret, however, and many managers
may prefer the (simpler) extended p chart.