Portfolio analysis involves the construction of a stock portfolio. Includes many market analysis tools.
This method shows us how to select and combine financial products by reducing risk. Often in the case of falling prices of one company is accompanied by a rise in prices of the second company, ie negative correlation.
Companies correlated negatively ie one price changes compensated by price changes of the other. There is also a specific risk involved in the operation of a single company generating profits for an investor. There is also a systematic risk that affects the functioning of the entire market dependent on many financial factors in the economy.
There will always be factors influencing the price of all stocks at the same time. Even if there are many companies in our portfolio, you can not eliminate the risk altogether.