Diary method involves filling respondents or participants in the study of special diaries recording of purchases, costs, consumption or use of any of the goods or services studied.

Diary method is more often used during:

• Retail audit. Sellers or owners of outlets are asked to fill in the entire arrival or sale of goods in a specially compiled diaries of purchases/sales. This method allows to more accurately assess the sale of goods in the retail network, especially in the absence of any control of sales by the outlets themselves.
• Media research. Diary panel in the measurement of television audience. This method involves the formation of a representative sample, that is, a sample, the structure of respondents which corresponds to the structure of the population of a region (city, region, country as a whole, etc.). The sample may include from several tens to several thousands of respondents, depending on the research goals and capabilities of the customer. Respondents included in this sample regularly (daily, weekly, etc.) fill in a special diary about what they did during this period of time. This method provides a clear record of the rating for each output of each TV program for each day. In other words, such a diary gives daily information on each of those channels, which are recorded TV viewing, the size of the audience of any transmission and the size of the audience of any 15-minute time interval, which is extremely important for advertisers. 
      
• Consumer panel. Respondents write goods or a group of goods that are consumed during a certain period in the diary. The question of who exactly is the buyer of a product, gives the answer using a technique such as consumer panel. The basic principles of its organization: a representative sample of the objects of study, the regularity of measurements, presentation of the results — remain the same as in the case of retail audit. However, the object of research is not outlets, but households and families. Moreover, the subject of the study are purchases (as well as all other income and expenses), which are carried out by the relevant family. Since it is almost impossible to record such purchases and the costs associated with them in the course of ordinary surveys (due to the fact that they cannot be remembered), the families chosen for the study are offered to keep a diary in which all purchases are recorded weekly and in detail (hence the second name of the technique — “diary panel”)..