You may use historical trending (like increses and decreases) to make a projection.
however, you must always note the nature of the stock markets now. Due to abnormal fluctuations, it is almost impossible to use current facts to predict. You may however, look at a similar case in the past i.e Great depression to project movements
Also research "regression/fitted lines". These are used by economists to come up with an equation that fits the values of historical data increases/decreases