Final answer:
The primary purpose of a common size statement is to analyze and compare the financial proportions within a company, facilitating comparisons across different-sized entities.
Step-by-step explanation:
The primary purpose of a common size statement is to analyze the relative proportions of different financial statement line items within a single company. This allows for the comparison of financial information across companies of different sizes by expressing financial data as percentages of a common figure, such as total assets or sales, rather than absolute numbers. By standardizing financial statements in this way, it becomes easier for analysts and investors to compare a company's financial structure and operations regardless of the company's size or the scale of its financials.