I've been working on a high school project attempting to determine whether or not there exists a relationship (and if it exists, information on the strength and duration of the relationship) between stock market data and election polls (both in time series format, n=250). While I'm moderately familiar on how to fit an ARIMA Model to a univariate time series using the Box-Jenkins approach, I've only encountered confusion when attempting to fit a model incorporating two variables.
Another response to a question similar to mine recommended using a transfer function, though I don't know if that would be applicable in my case as the goal is more to reveal information about a potential relationship, not necessarily to derive an exact formula linking the two series to be used for prediction. Implementing a bivariate ARIMA model in R appears to be as easy as simply adding an additional series, yet there seems to be surprisingly little literature on this or how to interpret such a model.