Final answer:
The most appropriate measure for describing variability in this data set, which includes a potential outlier, is the interquartile range (IQR) as it is not heavily influenced by extreme values.
Step-by-step explanation:
The question asks about determining the most appropriate measure for describing variability in a data distribution of games won by members of a chess club. Considering the provided data set {6, 6, 6, 7, 10, 11, 12, 13, 14, 14, 15, 16, 18, 18, 30}, we note that there is one particularly high value (30), which could be an outlier. Therefore, to describe the variability in this data set, a measure that is less affected by outliers, such as the interquartile range (IQR), would be more appropriate than options like variance or standard deviation. The IQR is the difference between the third quartile (Q3) and the first quartile (Q1), essentially measuring the spread of the middle 50% of the values.