What is an outlier in a data set?

An outlier in a data set is defined as a value that is significantly higher or lower than the other values in the same data set. This definition aligns with the choice indicating that an outlier is a value much greater or much less than the others. Outliers can arise from variability in the measurement or may indicate a measurement error. They often have a substantial impact on statistical analyses, as they can skew the results or affect the overall trends identified within the data.

In contrast, the other choices do not accurately describe an outlier. A value that represents the average refers to what is known as the mean, and does not capture the essence of an outlier situation. A commonly found value implies that it is part of the main distribution of the data set, which contradicts the definition of an outlier. Finally, a value that does not affect the overall data set suggests no significant deviation from the norm—this is also contrary to what an outlier is, since outliers are known for their potential to skew results and necessitate careful consideration in analysis.