CompTIA Data+ DA0-002 (V2) Practice Question

The correct answer is to use the interquartile range (IQR) to identify data points outside the main distribution. The IQR method is a standard and robust technique for identifying outliers because it is less sensitive to the extreme values themselves, unlike methods that rely on the mean and standard deviation. This method defines outliers as any data point that falls below Q1 - 1.5IQR or above Q3 + 1.5IQR.

Calculating the mean and standard deviation is part of the Z-score method for finding outliers, but the mean itself is heavily influenced by the suspected outliers, making it a less robust starting point in this scenario. Grouping data by customer ID is a form of aggregation that would help identify customers with high transaction frequency, not transactions with unusually high values. Checking for duplicate transaction IDs is an important data cleansing step to ensure data integrity, but it addresses a different type of inconsistency and would not identify a legitimate but unusually large transaction.