The purpose of asking participants in a research study to maintain product diaries is to obtain marketing research about which of the following?

Maintaining product diaries allows participants to record their purchasing habits over a specific period. This method provides detailed insights into consumers' buying behaviors, such as frequency of purchases, types of products bought, time of purchase, and brand preferences. By analyzing these diaries, marketers can understand trends and patterns in consumer behavior, which helps them tailor their strategies effectively to meet consumer needs and preferences.

The other options do not relate to the primary focus of product diaries. Financial skills involve the ability to manage money, viewing preferences pertain to media consumption choices, and essential needs address basic requirements for living. None of these aspects are directly captured through the act of documenting product purchases. Instead, the practice specifically targets how and what consumers decide to buy, making purchasing habits the correct focus for this research method.