What is the result of grouping data by a category and calculating a statistic for each group?

• A. A Single Global Statistic
• B. A Set Of Per-Group Statistics
• C. A Vector With No Relation To Groups
• D. A Reindexed Dataset With No Per-Group Breakdown

Answer: (B)

Grouping data by a category splits the data into blocks for each category. Calculating a statistic for each block then gives one value per category. So you end up with a set of per-group statistics—a summary that shows the statistic within each group, often shown as a table or a vector indexed by the category. This is different from a single global statistic and from a vector that has no link to the groups or a dataset with no per-group breakdown. For example, computing the average score by class yields an average for each class, not just one overall average.