Statistical data (also known as numerical or quantitative data) are frequently presented in the form of columns, charts, tables, or graphs that describe the amounts of something: warships, marriages, schools, or deaths from smallpox.

• Often numerical data will be given for different periods of time so that comparisons can be made (for example, the number of British warships in 1820, 1860, and 1900).
• Comparisons like these allow the reader to see the growth or decline of important events over time (the growth of a powerful state, the migration of a tribe, the number of people who owned telephones).
• When data about the past are sufficient and reliable, more complex mathematical operations can be performed (percentages, equations, and so on) that often bring to light previously unknown and at times unexpected facts about the past.