In investigating short-run cost fun

In investigating short-run cost functions using regression analysis, researchers have most frequently employed the time series technique with data for a specific plant or firm over time.It is important that when time series data are collected, the period over which observations are taken is limited to a relatively short span because the size of the plant or firm, as well as technology, should not change significantly during the time interval used in a short-run cost function. To conduct a meaningful analysis, there must be a sufficient number of observations, and there must be variations in production from observation period to observation period. Thus, each observation period, where possible, should be limited to a month. and sometimes even a shorter period (1 week or 2 week)