Dow theory was derived by Charles.H.Dow, this is old but a golden concept. This theory is derived by price patterns i.e., with market behaviour. This theory can can be analysed with minimum 2 years chart. With this, we can do 3 to 4 months trade.
The price patterns are derived by demand and supply, we need to spot tops and bottoms, where the higher bottom and higher top represents bullish trend, whereas the lower top and lower bottom represents bearish trend, but we should need to conform with volume.