Final answer:
An increase in retained earnings is directly explained by the company's net income for the period since profits that are not distributed as dividends increase the retained earnings balance.
Step-by-step explanation:
​Retained earnings are the portion of a company's profits that are kept or retained by the business and not distributed to shareholders in the form of dividends. Understanding the factors that can lead to an increase in retained earnings is crucial for analyzing a company's financial health. Of the options listed, net income for the period is the factor that would explain an increase in retained earnings.
When a company earns a profit and opts not to distribute it entirely as dividends, this profit contributes to the retained earnings balance. In contrast, the payment of dividends, a net loss for the period, and the issuance of additional shares of common stock do not directly increase retained earnings. Dividends decrease retained earnings; a net loss would also reduce it; and while issuing stock increases equity, it does not affect retained earnings unless it's issued at a premium which could lead to an increase in additional paid-in capital, not retained earnings specifically.