what is the definition of length of time series which model is the least likely to have an exact likelihood of using ols? how many observations are required for an arma model how is ols a model what tests are used to check the reliability of the model? length estimation time series how long should time series be how long of the time series does it take for an arma model when does the time series of an arma model need to be determined? what is time series length and likelihood length of time series and likelihood estimation length of time series what model is an ols length of time series a normal error model is called _________. how are the time series measured and a likelihood model developed for this model can be used? what is the average time series length how to estimate the likelihood in ARMA why use ols in a modelling what is the length of the time series for a typical arma what is the length of time series