1, research and analysis period. Some research and analysis need to choose a specific time period to explore a certain trend or change. For example, in the economic field, the data of 2007-202 1 may be due to the important financial crisis and recovery during this period, which requires statistical analysis.

2. Data availability. Some data may only contain data in a specific time period, so you can get the most complete data set by choosing this time period.

3. Compare with historical data. In some fields, such as statistics, market research and analysis, we can compare the current trend and data changes by selecting time periods including historical data, so as to better analyze the data and make predictions.